A Beginner’s Guide to Digital SLRs
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A Beginner’s Guide to Digital SLRs
by JamieFRST on Tue Jan 11, 2011 3:55 pm
Saw this on another car forum and thought it might be interesting for someone, as I know quite a few members have DSLR's
Think it originates from scoobynet.com after a quick google search, so credit to Richard ‘Hoppy’ Hopkins.
UNDERSTANDING PHOTOGRAPHY
A Beginner’s Guide to Digital SLRs
Many people new to the art and craft of photography find some of the terminology confusing and the theory complicated. But actually, once you understand the ground rules – and in the main they’re quite logical – it is pretty straightforward. And then, when you’re in control and start getting creative, you will understand what all the fuss and the fun is about. Here is a guide to knowing the basics. Enjoy J
What is so special about SLRs?
‘SLR’ stands for single lens reflex and this is the design of camera used by all keen photographers for decades. Most other types of camera have two lenses - one viewfinder lens for framing the picture, and a second lens that actually records the image. With an SLR, you view and frame the picture by looking through the same lens that records the image and in this way you can see exactly what the camera is getting. That’s what the Single Lens bit means. If you want to take more than casual snaps, this feature gives you much more precise control and it also allows you to use different lenses like long telephoto zooms, ultra wide angle lenses, or macro lenses for super quality close ups. And in all these situations, what you see in the viewfinder is exactly what you’ll get in the final image. This is not possible with other kinds of camera, and there are dozens of different lenses made to fit SLRs, not to mention powerful flash guns, and lots more clever bits and bobs that give you unrivalled versatility.
In order to make this single lens bit work, SLRs have a reflecting mirror and prism arrangement for viewing (that’s the Reflex part) and the instant before you take the picture the mirror flips up out of the way, allowing light to pass directly on to the digital sensor. This happens very quickly, in about 1/10th of a second, so is almost instantaneous. When the mirror is up, it blacks out the viewfinder while the shutter opens and the picture is recorded, then the mirror flips back down again for continued viewing. The whole operation happens in the blink of an eye.
All SLR cameras work like this, whether using film or digital, and the relatively new breed of ‘SLR-style’ digital cameras are different in that they do not have a reflex viewfinder. They are also known as bridge cameras in that they bridge the gap between more basic compact cameras and true SLRs. Viewing is by an LCD screen which is fed an image by the same sensor that records the final picture. It is a clever adaptation of digital technology but current models have some operational drawbacks, and you can’t fit different lenses. Of course, ever-improving technology will make these cameras better but they are unlikely to lure enthusiasts away from their beloved true SLRs where picture quality and versatility remain unparalleled.
Setting the Exposure
All digital sensors, like film, need a certain amount of light to give their best – not too much, and not too little. This is controlled by two key functions: the camera shutter which controls the duration of time the sensor is exposed to light, and by the lens aperture which controls the brightness of that light. For a given amount of light, if you double the duration of the shutter time, but also halve the size of the lens aperture, the effective amount of light reaching the sensor - the exposure - remains the same. Correct exposure is obtained by juggling these two settings, which can be used in a great variety of combinations. Both of them also have a big influence on how other aspects of the final picture will look, so understanding exposure gives you creative control at the same time.
Shutter speeds (durations of time) are marked in fractions of a second, eg 125 means 1/125th of a second, 250 is 1/250sec, 500 is 1/500sec and so on. It’s easy to see here that each speed is either half, or double, the one either side. Cameras can also give intermediate speeds, but the halving/doubling principle is fundamental to all aspects of exposure control. Remember that.
These shutter speeds might seem incredibly brief, but this is what you need to control movement. To freeze fast action, you will need 1/500sec or less, but you can also create intentional blurring by using a much slower speed, like 1/15sec or longer. You also have to balance this with your ability to hold the camera steady and avoid accidental blurring caused by camera-shake, or maybe use a tripod for steady support.
The lens aperture is a hole that controls the brightness of the light, by varying the size of the hole through which light passes to the sensor. The larger the hole, the brighter the light becomes, and this is set by adjusting the lens aperture, marked with an ‘f’ number. Now this bit can get confusing, but stick with it and the mists will be lifted. Large lens apertures are given a low f/number, like f/2.8 or f/4, and small lens apertures have a higher f/number, like f/11 or f/16.
Have you remembered that all exposure controls are linked by that halving/doubling/x2 factor? Well, believe it or not, so are these f/numbers. If you multiply, or divide, each f/number by the square root of two, which is 1.4, you’ll discover that f/2.8 is twice as large as f/4 (2.8 x 1.4 = 4) which is twice as large as f/5.6, and so on. The full range of f/numbers you’re likely to see is f/1.4, f/2, f/2.8, f/4, f/5.6, f/8, f/11, f/16, f/22, f/32 and each setting has either half or double the light passing area of the one either side. Your camera will also let you set intermediate lens apertures, like f/4.5 or f/5, which dovetail with intermediate shutter speeds to give you the best result, so it’s a neat mix and match.
A given f/number is always constant and directly comparable in the amount of light it allows to pass, regardless of lens, camera, or sensor size. This applies to everything from a camera-phone, to zoom lenses, or to those massive super-long professional telephoto lenses. An f/number is already adjusted for these variables because it’s a ratio between the focal length of the lens and diameter of the aperture. So f/numbers are directly comparable in terms of exposure control, but depending on the focal length of the lens you’re using, different f/numbers have a major role to play in deciding which parts of the picture you want to be sharp, and which parts blurred, which we’ll come to later.
Decisions, decisions! Are you following this? Making different choices is at the heart of good photography. This is crucial stuff, so there’s a little test to follow.
Finally, with digital SLRs, you can also control the sensor’s sensitivity to light by adjusting the ISO number (International Standards Organisation). Here we thankfully return to logical numbers, and the halving/doubling principle is obvious: ISO 100 needs twice as much light as ISO 200, which needs twice as much as ISO 400 and so on. But the really good news is that, unlike film cameras where you are stuck with whatever ISO rating a particular film has and there is always a big penalty in image quality for choosing a higher sensitivity film, with digital you can increase the ISO setting at any time. And while there is some loss of detail in the darkest parts of the image, it is usually hardly noticeable and picture quality remains very good. This really is a photographer’s dream come true, so make the most of it.
Okay, see if you’ve got it with this test. You’re shooting motor sport with your new digital SLR and the action is hot. Your camera says 1/125sec at f/8, set at ISO 100, but you want to freeze the action with a shutter speed of 1/500sec. What adjustments can you make to maintain correct exposure, but using a shutter speed of 1/500sec? There are two answers at the end*.
What is correct exposure?
Modern technology is very clever and your camera can measure and interpret complex situations extremely quickly and accurately. So the simple answer to correct exposure is, if it looks right to you, then it is right. Check the screen of your D-SLR. Looks okay? Take a glance at the histogram graph of light levels (see your camera handbook). If that’s okay too, and histograms are very easy to understand, then no worries.
However, if the image does look too light or too dark, then you need to adjust the exposure with the compensation control. If it’s too light, then that’s over exposure and you need to reduce the amount of light reaching the sensor. You must dial in some minus compensation and take another test shot. If the image is too dark, that’s under exposure and you need to increase the light with plus compensation. With a D-SLR, taking a test snap is quick, easy and decisive, so use this facility. You new guys don’t know how lucky you are.
Photo Jargon Explained
What is a stop? What is a fast lens, what is a fast or a high shutter speed, or indeed a slow shutter speed, and what is a sensor’s ISO speed? This is all photographer’s slang and sometimes the meaning is clear and logical, and sometimes it’s, well, strictly speaking wrong but kinda makes sense.
A lens stop is its f/number and goes way back to when the light entering a lens was controlled by a piece of wood with a hole in it. A smaller hole would ‘stop’ more light, and each hole was half or double the area of the next size, as with our f/numbers now. That’s where the term originated but today a stop has become shorthand for a halving or doubling of anything exposure-wise and is also often applied to shutter speeds as in “go a stop faster” which more accurately translates to “halve the shutter duration” but you get the drift.
A fast lens is one with a large maximum aperture (low f/number) such as f/2.8 or f/2. It’s fast because it allows you to use a fast shutter speed, which is slang for a short-duration shutter speed like 1/500sec or 1/1000sec that will help to freeze fast action. Likewise, fast film or fast ISO settings refer to high sensitivity to light, which also allows you to use shorter duration shutter speeds. And in all these situations, the term slow may also be heard – it means (pleasant surprise) the opposite of fast.
From these basic explanations, you will appreciate that photographers are generally obsessed with how bright the light is – always have been, and always will be. The fundamental issue is that the difference between what you see with your eye and brain combination and what your camera can record, is massively one-sided and the camera loses every time. Almost always, you can’t have too much light. On the rare occasions when this might possibly be a minor inconvenience, it is easy to control. But if you haven’t got enough light, which is very common, it can be difficult. Man might have invented the flashgun, but it’s a poor substitute for that big bright thing in the sky.
Lens Focal Length
The focal length of a lens is a measure of the distance from the centre of the lens to the image sensor. This distance also effects magnification of the image it will produce. Long focal lengths like 200mm or 400mm are called telephotos and will make distant subjects appear larger. Good for sport, nature, and other subjects where you can’t get close to the action.
At the other extreme, short focal length lenses like 15mm or 24mm are called wide angles because they take in a wide view, which is good for landscapes, or cramped situations where you need to include everything in the picture.
In-between these focal lengths are standard lenses, which will often come already fitted to the camera as part of a kit, and are good general purpose lenses. You can have a go at most things with these, and they’ll handle popular subjects like portraits and close ups quite well.
Of course, most popular lenses today are zooms. A zoom lens varies its focal length and most fall into the broad categories mentioned above, such as tele zooms, wide angle zooms or standard zooms. They will typically have a zoom range of around 3x, which means the longest focal length is about three times the short focal length, eg 70-210mm (70 x 3 = 210). Generally, the lower the zoom range of a lens, the better the image quality will be, but that’s not always the case as cost plays a big part. Many lenses cost several times the price of the camera.
There are also zooms with a focal length range that goes all the way from wide angle to telephoto in one neat package, sometimes called super zooms with a zoom ratio of maybe 10x, which is extreme. They are very handy, but some corners have to be cut in their optical design so image quality is often lower than less ambitious lenses. They will still beat any lens fitted to a non-SLR, but compared to the best SLR lenses their image sharpness will be slightly lower, there will be some vignetting which means corners of the picture will be slightly darker, and there will be some distortion where straight lines near the edges of the picture are slightly curved, such as the walls of a building. You may also notice something called chromatic aberration (CA) particularly at the wide angle end. This shows up as colour fringing around the edges of light/dark areas, often pinkish or green, and most obviously towards the outside of the picture. Finally, the maximum aperture of these lenses is always relatively small, especially at the telephoto end, which is the opposite of what you want.
Having said all that, most other lenses also suffer at least some of these minor problems, and many image quality issues can be largely eliminated by post-processing with your PC if you have a little time and skill, with Photoshop software for example. And some people love the convenience of super-zooms and use nothing else, while others hate them and will have a bag full of separate lenses, each one tailored to a particular purpose. It depends how picky you are, not to mention the cost, but photographers are always searching for better lenses in an endless quest for perfect pictures. Most will have at least two or three lenses, and lust for more. It is easy to fall in love with these beautiful toys, and lose sight of what you want them for in the first place. A useful catchphrase to is “zoom your feet” which means that very often just getting yourself into the best shooting position will produce much better pictures than any costly lenses.
Image Format and Focal Length
While the focal length of a lens affects image size, this only becomes really meaningful when it is nailed directly to an image format (sensor size). This is when you can measure the angle of view – how much, or how little, you’re getting in the picture - and begin to see what a lens is really capable of. With the introduction of digital cameras, using a variety of different sized sensors, this can get a bit complicated, but it needs to be understood before you can make sound choices.
Pre-digital when we all used film, popular cameras had a 35mm format. This measure refers to the overall width of the film, including the sprocket holes. The actual size of the image frame is 24 x 36mm, and this is referred to as Full-Frame 35mm (FF-35mm). Most D-SLR cameras use an image sensor that is less than half this size, so they need different focal length lenses to produce the same angle of view. To help you understand what you’re getting in the picture, you will see the term 35mm equivalent used as a reference to focal length. For example, a 17-85mm lens for a Canon D-SLR might also be described as a 28-135mm equivalent. This means that the lens has the same angle of view as a 28-135mm lens on a FF-35mm camera.
These calculations would not be necessary if all lenses were marked with their angles of view, but they’re not so you need to do a focal length conversion. Manufacturers make it easy by quoting a crop factor for their D-SLRs, which is related to how much their image sensors have been cropped (reduced in size) compared to FF-35mm, and it allows you to easily convert focal lengths into their 35mm equivalents and make comparisons. For example, Canon’s popular range of D-SLRs has an image sensor that is less than half the size of FF-35mm, and you need to multiply the actual focal length of a lens by 1.6x to calculate the FF-35mm equivalent focal length. Nikon use a 1.5x crop factor, and most other brands are similar.
There are also a few FF-35mm D-SLRs around, which of course do not require any adjustment for focal length. The large image sensor also delivers fantastic picture quality even in the biggest enlargements, but they are also very expensive and intended for professionals. The new smaller sensors of D-SLRs aimed at the consumer market are much cheaper, they are here to stay and are getting better all the time. Manufacturers are also producing new lenses specifically for these cameras, which are optimised for the smaller image sensor, and this is a sure sign of commitment to the future.
Lens numbers – what do they mean?
As an example, we’ll take the 17-85mm Canon lens mentioned before. Around the front of the lens it reads 17-85mm 1:4.5-5.6. The focal length range is 17-85mm and the largest f/number is f/4.5 at 17mm, and this reduces slightly to f/5.6 when the lens is zoomed out to 85mm. Only the lens’s maximum (largest) aperture is ever quoted and this is always preceded by the number 1. This is another ratio, but since every lens always quotes the same value of 1, you can ignore it.
This lens also has EF-S USM IS written on it, which are exclusive Canon abbreviations. Canon’s main lens range is tagged EF and these lenses can be used on any of its SLRs, but their EF-S lenses are specifically designed for the smaller sensor size of its popular D-SLRs. USM stands for Ultra Sonic Motor, as used in its virtually silent auto focusing mechanism, and IS refers to its Image Stabilization lens technology, which reduces the effect of camera-shake that can easily blur images (see later). Most other manufacturers offer similar features, identified with their own shorthand initials.
Depth of field
Depth of field is one of the key aspects of an image that can be controlled to great creative effect. It is also one of those photographic techniques often surrounded in mystery.
Depth of field is the zone of sharpness within a picture – the area that is in clear focus from close to the camera, towards the distance. In a wide-angle landscape picture, it can extend from your feet right to the horizon, or in a close-up of a butterfly it can be just an a few millimetres of exquisite detail with everything else a complete blur. You choose.
Imagine a good portrait, with head and shoulders turned slightly towards the camera. You’ll see that the eyes are crystal clear, but closer to the camera the near shoulder will be slightly out of focus, and behind the subject, the background will be completely out of focus. The photographer has deliberately chosen to use shallow depth of field, creating a zone of sharpness only about six inches deep – that’s the depth of field - with the main point of focus on the eyes to concentrate your attention on the face, and everything else nicely blurred to reduce distractions in the foreground and background. It might be easier to grasp if this zone of sharpness was called depth of focus but that term actually refers to something different, even though it is often confused with depth of field.
There are just two factors that control depth of field - the size of the lens aperture (f/number), and the size of, or magnification, of the image. Let’s look at each factor, starting with the easy one.
Large lens apertures (low f/numbers) like f/2 or f/2.8, give shallow depth of field, and small lens apertures (high f/numbers) like f/11 or f/16, give much deeper depth of field. Selecting the f/number is the main control used to determine depth of field when setting the exposure and composing the picture. So, lenses with large apertures not only give you more options when it comes to setting the exposure, they can also be used to reduce depth of field. As in the example above, wide-aperture lenses are good for portraiture, and because they can simultaneously allow a fast shutter speed, they are also good for action photography, or for taking pictures in low light. Not only that, but you get a brighter viewfinder image for easier focusing and composition. No wonder that fast lenses are so sought after by photographers - what’s the catch? They are usually big and heavy, and are always more expensive.
Image size is the other factor that determines depth of field, and the bigger the image appears in the picture, so the depth of field reduces. But there is a slight complication in that there are two ways of varying the image size. The most obvious one is that if you move closer to the subject, the image gets bigger. Alternatively, if you fit a longer focal length lens such as a telephoto, this will magnify the image making it bigger and so this also reduces depth of field.
It is often said that telephoto lenses reduce depth of field, and they can, but they only do this by increasing the image size. Let’s take our portrait again as an example. If you frame your subject for a head and shoulders picture with a standard focal length lens, at a given f/number you will have a certain amount of depth of field. If you then fit a telephoto lens, but also move back so that once again your subject appears the same size in the viewfinder, then at that same f/number the depth of field will be identical.
It is untrue to say that telephoto lenses always produce less depth of field, for the reason given above, but there is a little more to consider here in order to get a full and true understanding. In some circumstances, telephoto lenses can appear to give less depth of field. This is because telephoto lenses have a narrow angle of view, and therefore when you move back and shoot from a more distant position, there is less background appearing in the picture, behind the main subject. This usually gives the impression that depth of field is reduced and although it is actually an illusion, it is one that can be used to great pictorial effect.
By the same token, the reverse of this phenomenon applies to wide angle lenses that are often said to give greater depth of field. They don’t, but from a fixed camera position they will make the image smaller, and that does increase depth of field. Likewise, the wide angle of view will include more background and while this doesn’t actually increase depth of field, it often looks that way.
Finally, with the introduction of digital cameras, there is now another aspect of image magnification to consider – the size of the sensor. We’ll not dwell on this as there are a lot of variables to consider, but simply say that the smaller the sensor, the greater the depth of field will be. Basically, a D-SLR with a sensor crop factor of 1.5x or 1.6x will produce images with significantly greater depth of field than FF-35mm SLRs. The difference is about two stops, so that f/5.6 on a 1.6x crop SLR will deliver approximately the same depth of field as f/11 on FF-35mm. This can be an advantage or a disadvantage, depending on the type of photography you do. And of course, the effective focal length changes also, so you have to be careful with comparisons.
That’s a lot to take in, so here’s a quick reminder. Large lens apertures (low f/number) and large image size (move closer, use a telephoto) reduce depth of field. And cameras with an image sensor smaller than FF-35mm have greater depth of field. If you want to know exactly what your depth of field is going to be, most SLRs have a button that closes the lens down to the picture taking f/number you’ve selected so that you can see for yourself. Unfortunately, this often makes the image too dark to see easily so you can buy a simple calculator that will tell you the exact distances, or even more simply, download a very good DIY version from here: http://www.dofmaster.com/dofjs.html
Understanding the shutter
SLRs use a focal plane type shutter to control the duration of the exposure, so called because it sits behind the mirror and immediately in front of the image sensor’s focal plane. It is one of the few hard working mechanical components of a modern camera, and is capable of taking tens of thousands of exposures, as briefly as 1/8000sec, and sometimes at a rate of over 5fps (frames, or photos, per second).
Yet the secret of this amazing piece of machinery lies in its ingenious simplicity, rather than great complexity. It actually operates at only one, fixed speed, resulting in a finely tuned and uncompromised mechanism that is both reliable and consistent. The fixed speed is usually around 1/125sec (it will be the speed marked for flash synchronisation – x-sync - on the camera) and it is only at this speed, or longer, that the entire surface of the image sensor will be uncovered at any one moment, and the much shorter exposure times that it can produce are something of a trick.
Here’s how it works. There are two moving metal blinds that cover the image sensor. They used to be made of cloth, and are still referred to as curtains. When the shutter release is pressed, powerful springs fire the first curtain and it travels downwards over the surface of the sensor, exposing it to light. After a brief delay determined by the shutter speed selected, the second curtain does the same thing, covering over the sensor again, and terminating the exposure.
The way it produces variable exposure times lies in the delay before the second curtain is released. As mentioned above, at a shutter speed of around 1/125sec, the second curtain will not begin to move until the first curtain has reached the bottom and uncovered the whole of the sensor. But to create shorter exposure times, the second curtain will move before the first curtain has reached the end of its travel. In this example using 1/125sec, if the second curtain starts to travel when the first curtain is only half way down, the effective exposure time will be halved, ie 1/250sec. As the shutter speed is increased, so the delay between the first and second curtains is progressively reduced, and when running at the highest speed, the gap between the first and second curtains will be only 1-2mm as they travel down in tandem over the sensor.
It’s a neat trick, but there is one drawback and that is that flash can only be used at slower shutter speeds, up to the maximum x-sync speed. This is because the duration of the flash is very short, 1/1000sec or less, and if the whole of the image is to be evenly exposed by flash, it must be fired when the entire image sensor is uncovered by the shutter. Clearly, if the flash was to fire at higher speeds, it would only expose a band across the image – just the gap between the shutter curtains as they travel down close together.
Creative use of shutter speeds
We’ve read that the shutter speed is used to control the exposure and also allow different lens f/numbers to be chosen to vary depth of field. Its other function is to control movement.
The most obvious situation is when you use a fast shutter speed to freeze action. That is straightforward enough, although you may be surprised how fast you need to go – anything longer than 1/500sec is not really that fast, and you’ll need 1/2000sec to see something like droplets of water frozen like ice in a fountain.
Or you can look at it another way and choose a longer shutter speed. Shoot that same waterfall at 1/20sec and the droplets will turn into a slightly blurred stream of water, much as it appears to the naked eye. The human eye cannot detect movement any quicker than 1/20sec or so, which is why TV images show smooth movement, even though they are composed of a sequence of still images, but when presented at the rate of 25fps the eye cannot see the gaps in between. With the waterfall, go further still and at 1/2sec the water stream will begin to look quite surreal and more like clouds than water. You will need a tripod to use long shutter speeds like this.
You can also deliberately introduce blur to emphasise the impression of speed and movement with a popular technique known as panning. Panning is when you move the camera to follow the subject, often using a mid range shutter speed like 1/125sec or 1/60sec. The subject should remain relatively static in your viewfinder as you track it, but the background is rushing past in a blur emphasised by the slightly longer shutter speed. Not only is the impression of speed enhanced, but the blurring of the background makes the main subject stand out more. Panning is a great technique, but needs practise. The secret is smooth and accurate tracking of the subject, but even the experts will take two or three shots if possible. A monopod is a very useful accessory to help give your panning skills a boost.
It is not only the subject that is likely to move in your pictures, so will the camera unless it is bolted down to a heavy tripod. Camera shake is the result of trying to hand-hold the camera when using a shutter speed that is too long. Camera shake is very common, and while it is often obvious, more often it is not so obvious but just takes the edge off a nice sharp picture. You might blame the lens, or poor focusing, but it’s just as likely to be your unsteady hand.
Using telephoto lenses emphasises camera movement, in the same way that it can sometimes be hard to hold a pair of binoculars absolutely steady. There is a popular rule of thumb that can help you judge the slowest shutter speed that you can use with confidence, and that is the shutter speed should never be slower than the focal length of the lens, so if you use a 200mm lens, don’t go slower than 1/200sec. However, this old rule must be qualified, corrected, and taken with a large pinch of salt.
To start with, this guide only applies to FF-35mm cameras and because the effective focal length is increased by the crop factor on most D-SLRs, the new 35mm equivalent focal length must be used. So on a Canon D-SLR with a 1.6x crop factor, 200mm becomes 320mm, and therefore your slowest shutter speed should be 1/320sec.
But even more importantly, you, the photographer, must also be figured into the equation. Nobody’s hands are the same, and how steadily you can hold the camera will also depend on the picture-taking situation. Are you standing upright, relaxed and leaning against a wall for extra support, while holding the camera tight to your chest? Or are you down on one knee, and stretching uncomfortably to get just the view you want? The difference between these two examples in terms of the shutter speed you need to guarantee a sharp result will be at least two stops (to use the photographers’ jargon) so that 1/320sec needs to be raised to 1/1250sec in the latter circumstances.
One of the best experiments you can ever do, that will only take an hour or so but will benefit every picture you will ever shoot from now on, is to take a series of test pictures with different focal length lenses and in different shooting positions, and compare the results. You will need a tripod in order to get a perfectly sharp image to compare your hand-held shots against. Choose a distant subject so that there’s no danger of inaccurate focus affecting the results and run through as many different shutter speeds as you can, with as many different lens focal lengths as you’ve got, and in various shooting positions. Take several pictures each time. With digital, it is so easy to do this and blow them up on your PC monitor to see just how steady you actually are, compared to the tripod images, and draw up your own personal hand holding formula.
When you’ve done this, you’ll be pleasantly surprised that with wide angle lenses, you can often hold the camera steadily enough to use quite long shutter speeds. The benefits of this are obvious in terms of the exposure settings and the depth of field options it gives you. Wouldn’t it be wonderful if you could get away with using longer shutter speeds all the time? Well, now you can, and without using a tripod.
There is new technology available that has a dramatic effect on steadying your shaky hands. Canon call it Image Stabilization (IS), Nikon call it Vibration Reduction (VR) and most manufacturers offer something similar. They all use movement detectors coupled to electronically driven optical devices that cancel out camera shake significantly. Canon claims its IS system allows you to shoot at shutter speeds up to three stops longer than would normally be possible. That’s the difference between 1/500sec and 1/60sec - quite a claim, but it is true. There’s only one caveat, and that is if you need 1/500sec to freeze action, then shooting at 1/60sec with IS is still going to give you a blurred subject. Nevertheless, this is a major and extremely practical technological breakthrough, and even the extra cost is reasonable.
Automatic exposure modes
All D-SLRs have a wide range of exposure control options which provide endless creative permutations to explore. They range from fully Manual operation (M) where every control setting is made by you, through semi automatic where you make the main choices and the camera does the rest, and on to fully automatic Program (P) where all you have to do is point and shoot.
There will also be a selection of Basic Exposure Modes, which are marked with a symbol depicting popular subjects like action, or a portrait or landscape, and so on. These modes will set the exposure fully automatically, but will also bias the shutter speed and lens aperture selection to give the best pre-programmed result for the type of subject you’ve selected.
For example, if you select the action symbol, the camera will always try to use the fastest shutter speed it can, according to the brightness of the light available. For a portrait, it will assume you want shallow depth of field and will chose a wide lens aperture, and for landscapes it will go for maximum depth of field, so setting a small lens aperture.
Clever stuff? Well, yes and no.
For action photography, you will often want a fast shutter speed to freeze movement, but not if you’re panning and want a slower speed to help blur the background. For a close-up portrait, you would usually go for a wide lens aperture for shallow depth of field, but if you want to show some of the background to illustrate the subject’s environment, you would probably opt for a smaller lens aperture and zoom back for a wider view.
In situations like these, the semi-automatic modes can be very useful. There are two, marked Tv (Time value) and Av (Aperture value). With Tv, you set the shutter speed you want and the camera will automatically match it with the correct lens aperture. It will also vary the aperture if the light changes while you’re busy concentrating, so that’s one thing less to worry about. Setting Av does the same thing, but in reverse of course, after you have selected the lens aperture.
How many pixels do you need?
Pixels were once the be-all and end-all of any digital decision, but it has now reached a stage where the sharpness of digital pictures is often higher than you can even see or print. The quality of film, supreme for over a century, is now beaten and chasing ever-higher pixel counts needs to be considered in context. For example, if you never make prints larger than 6 x 4in, then, believe it or not, anything more than 2m pixels is wasted - printers cannot reproduce any finer detail, and unless you squint and look very closely, you can’t see it, either! Be wary of trying to measure a camera’s pixels-per-inch count (PPI) against the dots-per-inch (DPI) of a printer as printers use several dots to reproduce one pixel, depending on the colour, so comparisons are difficult.
Moving up to A4 prints – the size of a full magazine page - requires no more than 5m pixels maximum. In practise, you can get very high quality prints of this size from a camera with less pixels, mainly because larger prints are always viewed from a little further away, and clever image enhancement software can make a big difference.
But having said that, it is always nice to have a little more resolving power in hand, a few more pixels, for big enlargements and for zooming-in at the printing stage to get the best composition, but without losing sharpness. Just bear in mind that it’s not only pixels that matter and at larger print sizes, it is quite likely that the resolving power of the lens (its ability to show fine detail) will also be exceeded in some situations, or that your focusing accuracy will be slightly out, or that the image will be degraded by camera shake. So, if you are seeking ultimate image quality, in addition to pixels you must also ensure that your lenses are the best available, that you have a high quality photo printer using six or more inks (not just four) and that you always use the highest quality printing paper. Last but certainly not least, your photographic and digital processing techniques have got to be absolutely impeccable.
JPEG and RAW images
D-SLRs are mini computers that contain sophisticated image processing software to help you get the best quality photos. The two most popular types of image file are JPEG (Joint Photographic Experts Group) and RAW (which just means unprocessed).
JPEG processing is a universal standard that both enhances and compresses image files, and it works very well. Unless you intend to spend time post-processing with specialist software like Photoshop, JPEG is the one to use. You can select different standards of JPEG compression, and at the highest quality settings it is almost impossible to detect, but the big bonus is substantially reduced file sizes – you can get hundreds of pictures on to a 1Gb memory card. The camera can also handle these smaller files much more easily, so if you are shooting fast action at maybe 5fps, the camera will keep going longer before the buffer is filled and you are forced to stop for a few seconds while data is transferred to the memory card.
You can also customise JPEG processing by adjusting sharpness, contrast, saturation and colour tone levels in the camera to get just the kind of photos you like. The camera’s default settings are usually a good starting point, but to see the effect these adjustments to levels make, do some test prints and compare. It’s similar to adjusting the picture settings on your TV, but bear in mind that what comes out of the camera might not look exactly the same on your PC monitor, and may be slightly changed again by your printer. This is not a fault and it is possible to get all your devices calibrated together, but you can usually fix things yourself with a few simple adjustments.
RAW is for experienced users who want the absolute maximum quality possible and are prepared to put the work in to get it. RAW is the digital equivalent of the film negative and takes the whole image file from the sensor and records it on the memory card without any compression by the camera. Unprocessed RAW images often don’t look their best, so you must post-process them with a PC and software, but then you will be rewarded with outstanding results.
Some cameras allow you to shoot both RAW files and JPEGs simultaneously, giving you the best of both worlds, but RAW files are also huge. Their size varies according to the number of pixels but they are many times larger than JPEGs, and will fill up your memory card quickly.
Flash in daylight
Flash doesn’t have to be used at night – it can also produce wonderful pictures in daylight. The technique is called fill-in flash, when the flash is used to fill-in dark areas of shadow. It works particularly well for portraits.
If your subject is facing the sun, they will squint and look uncomfortable. So turn them around, so that the light is shining from the side or from behind. With the sun in their hair, they’ll look great (girls, guys, kids - it doesn’t matter). But now the face will be in shadow and if you make a normal exposure, the camera will see lots of bright light that will lead to under exposure of the face. That will give you a silhouette.
You now have two options to correct this: firstly, you could dial in some plus exposure compensation, which will lighten the face, but will bleach the bright background into pure white. Ideally, what you want is to balance the attractive bright light coming from behind with more light from the front. You could do this with a reflector, but they are big, cumbersome, and tend to get blown away (literally!), so your second easy option is to use fill-in flash. Fortunately, fill-in doesn’t need much power so the built-in flash will be fine, and the camera will do all the exposure calculations for you, to ensure a good balance between the daylight and flash. It will also prevent you from using a shutter speed faster than the x-sync speed, lest you forget. Easy, and it looks great with the flash also putting a nice highlight in the eyes.
Flash at night
When the sun goes down, a lot of easy picture taking opportunity goes with it. Artificial light, from either ordinary light bulbs or fluorescent tubes, is much less bright than sunlight and even though you can see perfectly well, your camera cannot do the same Also, most kinds of artificial light are not the same colour as daylight, and you should adjust your camera’s white balance control to get natural looking pictures. But don’t give up – you just need to try a little harder. Crank up the ISO, open the lens to its largest aperture, use the IS or VR feature if you have it, and hone your technique with careful focusing and a steady hand. Your reward will be photos full of natural atmosphere.
Or you can use flash. While flash is no substitute for daylight, if you understand its strengths and weaknesses, you can adapt to its limitations and get some great pictures.
Red-eye is a common problem, so common that there are several tricks that camera makers use to get rid of it. None of them works very well, although many software programmes can detect and eliminate it quite effectively in post-processing. But it’s much better to avoid it in the first place.
Red-eye is caused by light from the flash reflecting back off the retina of the eye, directly into the lens. It is worst when the distance between the flash head and camera lens is short, so moving the flash away from the lens is an instant cure. However, if the flash is built-in to the camera, this is obviously impossible and a good reason to buy a separate flashgun. This will have much more power and can be used in different positions and in various ways to greatly improve your flash photography.
Bounce flash is one technique that you can use with a more powerful gun, and it will eliminate red-eye, give soft natural looking light, and get you around a tricky bit of physics called the inverse square law.
The inverse square law simply means that if you double the distance from the flash to the subject, the light is reduced to one quarter. Try it yourself by pointing a torch at a plain wall and measure the circle of light. Move back to double the distance and when you measure it again, the circle of light will be four times the area and so also a quarter of the brightness.
Here’s a familiar example where the inverse square law explains those horrible snaps we’ve all taken at parties where someone’s face close to the camera is bleached ghostly white, while other people just a few feet away are almost too dark to recognise. Here’s why – if the nearest person was two feet from the flash, then people four feet away will be lit by only one quarter of the light, and eight feet away the light is reduced to one sixteenth. That is far too great a range of brightness and the solution is firstly to move back so that the greater distance reduces the rate at which the light diminishes, then try and arrange your picture so that all important areas are roughly the same distance from the flash. Finally, point the flashgun at a white ceiling and it will flood the room with light as the flash bounces off the ceiling and down again. It’s a really easy technique as all the complex exposure calculations are handled by the camera. The only problem may be a lack of flash power – bounce flash just gobbles light, so always buy the most powerful flashgun you can.
Composition
This is a controversial topic, where rules are often best when broken, so we’ll stick to some simple basics. Perhaps the best advice on composition is to stop, look and think. Now read that again, slowly. Take your time, and then choose your moment. Don’t just pick up the camera, zoom in and fire off a few frames in the hope that one will be good. Chances are that it won’t.
If you can, walk around your subject, seek out interesting angles, and if you have an eye for a picture (and most people do) very often things will click into place, the composition will work and the picture will look balanced.
And when the picture does look right and well balanced, you’ll usually find that key areas of interest correspond with the Rule of Thirds. It works like this. Imagine a rectangle, say 6 x 9 inches. Along the 9in side, measure 3in from the edge and draw a line to the opposite side, move along another 3in and draw another line. Now move to the shorter side, measure 2in in and draw a line across, then move another 2in and do the same again.
Your basic rectangle will now be divided into nine smaller rectangles, and the lines will intersect at four points around the centre of the frame. These four points, each one a third in from the outside edge, are the points referred to in the Rule of Thirds where the eye tends to rest naturally when viewing an image. A simple test – imagine this template and overlay it mentally onto pictures that you like. You will be surprised how often keys areas of interest fall on one or more of the Thirds. It’s almost spooky.
A simpler way of putting it is to avoid putting key elements of the picture either right in the middle or close to the edges of the picture, but this is a little at odds with another good phrase to remember when composing your picture – Fill the Frame for Impact. For maximum punch, cut out all unnecessary detail, move in as close as you dare (and then a little more) and place your subject bang in the centre. It’s something of a shock tactic, but with the right subject, it is very powerful.
One more thing – lead in lines. These are often the key to great landscape pictures where the foreground sometimes adds nothing to the image and can even distract from the great view beyond. So look for a lead in line, often a road, river, a fence or wall, that attracts attention and then directs your eye from the edge and into the heart of the picture towards the centre of interest. This is hard (unless you have a portable wall to hand!) but when it works, it really makes the picture.
Think it originates from scoobynet.com after a quick google search, so credit to Richard ‘Hoppy’ Hopkins.
UNDERSTANDING PHOTOGRAPHY
A Beginner’s Guide to Digital SLRs
Many people new to the art and craft of photography find some of the terminology confusing and the theory complicated. But actually, once you understand the ground rules – and in the main they’re quite logical – it is pretty straightforward. And then, when you’re in control and start getting creative, you will understand what all the fuss and the fun is about. Here is a guide to knowing the basics. Enjoy J
What is so special about SLRs?
‘SLR’ stands for single lens reflex and this is the design of camera used by all keen photographers for decades. Most other types of camera have two lenses - one viewfinder lens for framing the picture, and a second lens that actually records the image. With an SLR, you view and frame the picture by looking through the same lens that records the image and in this way you can see exactly what the camera is getting. That’s what the Single Lens bit means. If you want to take more than casual snaps, this feature gives you much more precise control and it also allows you to use different lenses like long telephoto zooms, ultra wide angle lenses, or macro lenses for super quality close ups. And in all these situations, what you see in the viewfinder is exactly what you’ll get in the final image. This is not possible with other kinds of camera, and there are dozens of different lenses made to fit SLRs, not to mention powerful flash guns, and lots more clever bits and bobs that give you unrivalled versatility.
In order to make this single lens bit work, SLRs have a reflecting mirror and prism arrangement for viewing (that’s the Reflex part) and the instant before you take the picture the mirror flips up out of the way, allowing light to pass directly on to the digital sensor. This happens very quickly, in about 1/10th of a second, so is almost instantaneous. When the mirror is up, it blacks out the viewfinder while the shutter opens and the picture is recorded, then the mirror flips back down again for continued viewing. The whole operation happens in the blink of an eye.
All SLR cameras work like this, whether using film or digital, and the relatively new breed of ‘SLR-style’ digital cameras are different in that they do not have a reflex viewfinder. They are also known as bridge cameras in that they bridge the gap between more basic compact cameras and true SLRs. Viewing is by an LCD screen which is fed an image by the same sensor that records the final picture. It is a clever adaptation of digital technology but current models have some operational drawbacks, and you can’t fit different lenses. Of course, ever-improving technology will make these cameras better but they are unlikely to lure enthusiasts away from their beloved true SLRs where picture quality and versatility remain unparalleled.
Setting the Exposure
All digital sensors, like film, need a certain amount of light to give their best – not too much, and not too little. This is controlled by two key functions: the camera shutter which controls the duration of time the sensor is exposed to light, and by the lens aperture which controls the brightness of that light. For a given amount of light, if you double the duration of the shutter time, but also halve the size of the lens aperture, the effective amount of light reaching the sensor - the exposure - remains the same. Correct exposure is obtained by juggling these two settings, which can be used in a great variety of combinations. Both of them also have a big influence on how other aspects of the final picture will look, so understanding exposure gives you creative control at the same time.
Shutter speeds (durations of time) are marked in fractions of a second, eg 125 means 1/125th of a second, 250 is 1/250sec, 500 is 1/500sec and so on. It’s easy to see here that each speed is either half, or double, the one either side. Cameras can also give intermediate speeds, but the halving/doubling principle is fundamental to all aspects of exposure control. Remember that.
These shutter speeds might seem incredibly brief, but this is what you need to control movement. To freeze fast action, you will need 1/500sec or less, but you can also create intentional blurring by using a much slower speed, like 1/15sec or longer. You also have to balance this with your ability to hold the camera steady and avoid accidental blurring caused by camera-shake, or maybe use a tripod for steady support.
The lens aperture is a hole that controls the brightness of the light, by varying the size of the hole through which light passes to the sensor. The larger the hole, the brighter the light becomes, and this is set by adjusting the lens aperture, marked with an ‘f’ number. Now this bit can get confusing, but stick with it and the mists will be lifted. Large lens apertures are given a low f/number, like f/2.8 or f/4, and small lens apertures have a higher f/number, like f/11 or f/16.
Have you remembered that all exposure controls are linked by that halving/doubling/x2 factor? Well, believe it or not, so are these f/numbers. If you multiply, or divide, each f/number by the square root of two, which is 1.4, you’ll discover that f/2.8 is twice as large as f/4 (2.8 x 1.4 = 4) which is twice as large as f/5.6, and so on. The full range of f/numbers you’re likely to see is f/1.4, f/2, f/2.8, f/4, f/5.6, f/8, f/11, f/16, f/22, f/32 and each setting has either half or double the light passing area of the one either side. Your camera will also let you set intermediate lens apertures, like f/4.5 or f/5, which dovetail with intermediate shutter speeds to give you the best result, so it’s a neat mix and match.
A given f/number is always constant and directly comparable in the amount of light it allows to pass, regardless of lens, camera, or sensor size. This applies to everything from a camera-phone, to zoom lenses, or to those massive super-long professional telephoto lenses. An f/number is already adjusted for these variables because it’s a ratio between the focal length of the lens and diameter of the aperture. So f/numbers are directly comparable in terms of exposure control, but depending on the focal length of the lens you’re using, different f/numbers have a major role to play in deciding which parts of the picture you want to be sharp, and which parts blurred, which we’ll come to later.
Decisions, decisions! Are you following this? Making different choices is at the heart of good photography. This is crucial stuff, so there’s a little test to follow.
Finally, with digital SLRs, you can also control the sensor’s sensitivity to light by adjusting the ISO number (International Standards Organisation). Here we thankfully return to logical numbers, and the halving/doubling principle is obvious: ISO 100 needs twice as much light as ISO 200, which needs twice as much as ISO 400 and so on. But the really good news is that, unlike film cameras where you are stuck with whatever ISO rating a particular film has and there is always a big penalty in image quality for choosing a higher sensitivity film, with digital you can increase the ISO setting at any time. And while there is some loss of detail in the darkest parts of the image, it is usually hardly noticeable and picture quality remains very good. This really is a photographer’s dream come true, so make the most of it.
Okay, see if you’ve got it with this test. You’re shooting motor sport with your new digital SLR and the action is hot. Your camera says 1/125sec at f/8, set at ISO 100, but you want to freeze the action with a shutter speed of 1/500sec. What adjustments can you make to maintain correct exposure, but using a shutter speed of 1/500sec? There are two answers at the end*.
What is correct exposure?
Modern technology is very clever and your camera can measure and interpret complex situations extremely quickly and accurately. So the simple answer to correct exposure is, if it looks right to you, then it is right. Check the screen of your D-SLR. Looks okay? Take a glance at the histogram graph of light levels (see your camera handbook). If that’s okay too, and histograms are very easy to understand, then no worries.
However, if the image does look too light or too dark, then you need to adjust the exposure with the compensation control. If it’s too light, then that’s over exposure and you need to reduce the amount of light reaching the sensor. You must dial in some minus compensation and take another test shot. If the image is too dark, that’s under exposure and you need to increase the light with plus compensation. With a D-SLR, taking a test snap is quick, easy and decisive, so use this facility. You new guys don’t know how lucky you are.
Photo Jargon Explained
What is a stop? What is a fast lens, what is a fast or a high shutter speed, or indeed a slow shutter speed, and what is a sensor’s ISO speed? This is all photographer’s slang and sometimes the meaning is clear and logical, and sometimes it’s, well, strictly speaking wrong but kinda makes sense.
A lens stop is its f/number and goes way back to when the light entering a lens was controlled by a piece of wood with a hole in it. A smaller hole would ‘stop’ more light, and each hole was half or double the area of the next size, as with our f/numbers now. That’s where the term originated but today a stop has become shorthand for a halving or doubling of anything exposure-wise and is also often applied to shutter speeds as in “go a stop faster” which more accurately translates to “halve the shutter duration” but you get the drift.
A fast lens is one with a large maximum aperture (low f/number) such as f/2.8 or f/2. It’s fast because it allows you to use a fast shutter speed, which is slang for a short-duration shutter speed like 1/500sec or 1/1000sec that will help to freeze fast action. Likewise, fast film or fast ISO settings refer to high sensitivity to light, which also allows you to use shorter duration shutter speeds. And in all these situations, the term slow may also be heard – it means (pleasant surprise) the opposite of fast.
From these basic explanations, you will appreciate that photographers are generally obsessed with how bright the light is – always have been, and always will be. The fundamental issue is that the difference between what you see with your eye and brain combination and what your camera can record, is massively one-sided and the camera loses every time. Almost always, you can’t have too much light. On the rare occasions when this might possibly be a minor inconvenience, it is easy to control. But if you haven’t got enough light, which is very common, it can be difficult. Man might have invented the flashgun, but it’s a poor substitute for that big bright thing in the sky.
Lens Focal Length
The focal length of a lens is a measure of the distance from the centre of the lens to the image sensor. This distance also effects magnification of the image it will produce. Long focal lengths like 200mm or 400mm are called telephotos and will make distant subjects appear larger. Good for sport, nature, and other subjects where you can’t get close to the action.
At the other extreme, short focal length lenses like 15mm or 24mm are called wide angles because they take in a wide view, which is good for landscapes, or cramped situations where you need to include everything in the picture.
In-between these focal lengths are standard lenses, which will often come already fitted to the camera as part of a kit, and are good general purpose lenses. You can have a go at most things with these, and they’ll handle popular subjects like portraits and close ups quite well.
Of course, most popular lenses today are zooms. A zoom lens varies its focal length and most fall into the broad categories mentioned above, such as tele zooms, wide angle zooms or standard zooms. They will typically have a zoom range of around 3x, which means the longest focal length is about three times the short focal length, eg 70-210mm (70 x 3 = 210). Generally, the lower the zoom range of a lens, the better the image quality will be, but that’s not always the case as cost plays a big part. Many lenses cost several times the price of the camera.
There are also zooms with a focal length range that goes all the way from wide angle to telephoto in one neat package, sometimes called super zooms with a zoom ratio of maybe 10x, which is extreme. They are very handy, but some corners have to be cut in their optical design so image quality is often lower than less ambitious lenses. They will still beat any lens fitted to a non-SLR, but compared to the best SLR lenses their image sharpness will be slightly lower, there will be some vignetting which means corners of the picture will be slightly darker, and there will be some distortion where straight lines near the edges of the picture are slightly curved, such as the walls of a building. You may also notice something called chromatic aberration (CA) particularly at the wide angle end. This shows up as colour fringing around the edges of light/dark areas, often pinkish or green, and most obviously towards the outside of the picture. Finally, the maximum aperture of these lenses is always relatively small, especially at the telephoto end, which is the opposite of what you want.
Having said all that, most other lenses also suffer at least some of these minor problems, and many image quality issues can be largely eliminated by post-processing with your PC if you have a little time and skill, with Photoshop software for example. And some people love the convenience of super-zooms and use nothing else, while others hate them and will have a bag full of separate lenses, each one tailored to a particular purpose. It depends how picky you are, not to mention the cost, but photographers are always searching for better lenses in an endless quest for perfect pictures. Most will have at least two or three lenses, and lust for more. It is easy to fall in love with these beautiful toys, and lose sight of what you want them for in the first place. A useful catchphrase to is “zoom your feet” which means that very often just getting yourself into the best shooting position will produce much better pictures than any costly lenses.
Image Format and Focal Length
While the focal length of a lens affects image size, this only becomes really meaningful when it is nailed directly to an image format (sensor size). This is when you can measure the angle of view – how much, or how little, you’re getting in the picture - and begin to see what a lens is really capable of. With the introduction of digital cameras, using a variety of different sized sensors, this can get a bit complicated, but it needs to be understood before you can make sound choices.
Pre-digital when we all used film, popular cameras had a 35mm format. This measure refers to the overall width of the film, including the sprocket holes. The actual size of the image frame is 24 x 36mm, and this is referred to as Full-Frame 35mm (FF-35mm). Most D-SLR cameras use an image sensor that is less than half this size, so they need different focal length lenses to produce the same angle of view. To help you understand what you’re getting in the picture, you will see the term 35mm equivalent used as a reference to focal length. For example, a 17-85mm lens for a Canon D-SLR might also be described as a 28-135mm equivalent. This means that the lens has the same angle of view as a 28-135mm lens on a FF-35mm camera.
These calculations would not be necessary if all lenses were marked with their angles of view, but they’re not so you need to do a focal length conversion. Manufacturers make it easy by quoting a crop factor for their D-SLRs, which is related to how much their image sensors have been cropped (reduced in size) compared to FF-35mm, and it allows you to easily convert focal lengths into their 35mm equivalents and make comparisons. For example, Canon’s popular range of D-SLRs has an image sensor that is less than half the size of FF-35mm, and you need to multiply the actual focal length of a lens by 1.6x to calculate the FF-35mm equivalent focal length. Nikon use a 1.5x crop factor, and most other brands are similar.
There are also a few FF-35mm D-SLRs around, which of course do not require any adjustment for focal length. The large image sensor also delivers fantastic picture quality even in the biggest enlargements, but they are also very expensive and intended for professionals. The new smaller sensors of D-SLRs aimed at the consumer market are much cheaper, they are here to stay and are getting better all the time. Manufacturers are also producing new lenses specifically for these cameras, which are optimised for the smaller image sensor, and this is a sure sign of commitment to the future.
Lens numbers – what do they mean?
As an example, we’ll take the 17-85mm Canon lens mentioned before. Around the front of the lens it reads 17-85mm 1:4.5-5.6. The focal length range is 17-85mm and the largest f/number is f/4.5 at 17mm, and this reduces slightly to f/5.6 when the lens is zoomed out to 85mm. Only the lens’s maximum (largest) aperture is ever quoted and this is always preceded by the number 1. This is another ratio, but since every lens always quotes the same value of 1, you can ignore it.
This lens also has EF-S USM IS written on it, which are exclusive Canon abbreviations. Canon’s main lens range is tagged EF and these lenses can be used on any of its SLRs, but their EF-S lenses are specifically designed for the smaller sensor size of its popular D-SLRs. USM stands for Ultra Sonic Motor, as used in its virtually silent auto focusing mechanism, and IS refers to its Image Stabilization lens technology, which reduces the effect of camera-shake that can easily blur images (see later). Most other manufacturers offer similar features, identified with their own shorthand initials.
Depth of field
Depth of field is one of the key aspects of an image that can be controlled to great creative effect. It is also one of those photographic techniques often surrounded in mystery.
Depth of field is the zone of sharpness within a picture – the area that is in clear focus from close to the camera, towards the distance. In a wide-angle landscape picture, it can extend from your feet right to the horizon, or in a close-up of a butterfly it can be just an a few millimetres of exquisite detail with everything else a complete blur. You choose.
Imagine a good portrait, with head and shoulders turned slightly towards the camera. You’ll see that the eyes are crystal clear, but closer to the camera the near shoulder will be slightly out of focus, and behind the subject, the background will be completely out of focus. The photographer has deliberately chosen to use shallow depth of field, creating a zone of sharpness only about six inches deep – that’s the depth of field - with the main point of focus on the eyes to concentrate your attention on the face, and everything else nicely blurred to reduce distractions in the foreground and background. It might be easier to grasp if this zone of sharpness was called depth of focus but that term actually refers to something different, even though it is often confused with depth of field.
There are just two factors that control depth of field - the size of the lens aperture (f/number), and the size of, or magnification, of the image. Let’s look at each factor, starting with the easy one.
Large lens apertures (low f/numbers) like f/2 or f/2.8, give shallow depth of field, and small lens apertures (high f/numbers) like f/11 or f/16, give much deeper depth of field. Selecting the f/number is the main control used to determine depth of field when setting the exposure and composing the picture. So, lenses with large apertures not only give you more options when it comes to setting the exposure, they can also be used to reduce depth of field. As in the example above, wide-aperture lenses are good for portraiture, and because they can simultaneously allow a fast shutter speed, they are also good for action photography, or for taking pictures in low light. Not only that, but you get a brighter viewfinder image for easier focusing and composition. No wonder that fast lenses are so sought after by photographers - what’s the catch? They are usually big and heavy, and are always more expensive.
Image size is the other factor that determines depth of field, and the bigger the image appears in the picture, so the depth of field reduces. But there is a slight complication in that there are two ways of varying the image size. The most obvious one is that if you move closer to the subject, the image gets bigger. Alternatively, if you fit a longer focal length lens such as a telephoto, this will magnify the image making it bigger and so this also reduces depth of field.
It is often said that telephoto lenses reduce depth of field, and they can, but they only do this by increasing the image size. Let’s take our portrait again as an example. If you frame your subject for a head and shoulders picture with a standard focal length lens, at a given f/number you will have a certain amount of depth of field. If you then fit a telephoto lens, but also move back so that once again your subject appears the same size in the viewfinder, then at that same f/number the depth of field will be identical.
It is untrue to say that telephoto lenses always produce less depth of field, for the reason given above, but there is a little more to consider here in order to get a full and true understanding. In some circumstances, telephoto lenses can appear to give less depth of field. This is because telephoto lenses have a narrow angle of view, and therefore when you move back and shoot from a more distant position, there is less background appearing in the picture, behind the main subject. This usually gives the impression that depth of field is reduced and although it is actually an illusion, it is one that can be used to great pictorial effect.
By the same token, the reverse of this phenomenon applies to wide angle lenses that are often said to give greater depth of field. They don’t, but from a fixed camera position they will make the image smaller, and that does increase depth of field. Likewise, the wide angle of view will include more background and while this doesn’t actually increase depth of field, it often looks that way.
Finally, with the introduction of digital cameras, there is now another aspect of image magnification to consider – the size of the sensor. We’ll not dwell on this as there are a lot of variables to consider, but simply say that the smaller the sensor, the greater the depth of field will be. Basically, a D-SLR with a sensor crop factor of 1.5x or 1.6x will produce images with significantly greater depth of field than FF-35mm SLRs. The difference is about two stops, so that f/5.6 on a 1.6x crop SLR will deliver approximately the same depth of field as f/11 on FF-35mm. This can be an advantage or a disadvantage, depending on the type of photography you do. And of course, the effective focal length changes also, so you have to be careful with comparisons.
That’s a lot to take in, so here’s a quick reminder. Large lens apertures (low f/number) and large image size (move closer, use a telephoto) reduce depth of field. And cameras with an image sensor smaller than FF-35mm have greater depth of field. If you want to know exactly what your depth of field is going to be, most SLRs have a button that closes the lens down to the picture taking f/number you’ve selected so that you can see for yourself. Unfortunately, this often makes the image too dark to see easily so you can buy a simple calculator that will tell you the exact distances, or even more simply, download a very good DIY version from here: http://www.dofmaster.com/dofjs.html
Understanding the shutter
SLRs use a focal plane type shutter to control the duration of the exposure, so called because it sits behind the mirror and immediately in front of the image sensor’s focal plane. It is one of the few hard working mechanical components of a modern camera, and is capable of taking tens of thousands of exposures, as briefly as 1/8000sec, and sometimes at a rate of over 5fps (frames, or photos, per second).
Yet the secret of this amazing piece of machinery lies in its ingenious simplicity, rather than great complexity. It actually operates at only one, fixed speed, resulting in a finely tuned and uncompromised mechanism that is both reliable and consistent. The fixed speed is usually around 1/125sec (it will be the speed marked for flash synchronisation – x-sync - on the camera) and it is only at this speed, or longer, that the entire surface of the image sensor will be uncovered at any one moment, and the much shorter exposure times that it can produce are something of a trick.
Here’s how it works. There are two moving metal blinds that cover the image sensor. They used to be made of cloth, and are still referred to as curtains. When the shutter release is pressed, powerful springs fire the first curtain and it travels downwards over the surface of the sensor, exposing it to light. After a brief delay determined by the shutter speed selected, the second curtain does the same thing, covering over the sensor again, and terminating the exposure.
The way it produces variable exposure times lies in the delay before the second curtain is released. As mentioned above, at a shutter speed of around 1/125sec, the second curtain will not begin to move until the first curtain has reached the bottom and uncovered the whole of the sensor. But to create shorter exposure times, the second curtain will move before the first curtain has reached the end of its travel. In this example using 1/125sec, if the second curtain starts to travel when the first curtain is only half way down, the effective exposure time will be halved, ie 1/250sec. As the shutter speed is increased, so the delay between the first and second curtains is progressively reduced, and when running at the highest speed, the gap between the first and second curtains will be only 1-2mm as they travel down in tandem over the sensor.
It’s a neat trick, but there is one drawback and that is that flash can only be used at slower shutter speeds, up to the maximum x-sync speed. This is because the duration of the flash is very short, 1/1000sec or less, and if the whole of the image is to be evenly exposed by flash, it must be fired when the entire image sensor is uncovered by the shutter. Clearly, if the flash was to fire at higher speeds, it would only expose a band across the image – just the gap between the shutter curtains as they travel down close together.
Creative use of shutter speeds
We’ve read that the shutter speed is used to control the exposure and also allow different lens f/numbers to be chosen to vary depth of field. Its other function is to control movement.
The most obvious situation is when you use a fast shutter speed to freeze action. That is straightforward enough, although you may be surprised how fast you need to go – anything longer than 1/500sec is not really that fast, and you’ll need 1/2000sec to see something like droplets of water frozen like ice in a fountain.
Or you can look at it another way and choose a longer shutter speed. Shoot that same waterfall at 1/20sec and the droplets will turn into a slightly blurred stream of water, much as it appears to the naked eye. The human eye cannot detect movement any quicker than 1/20sec or so, which is why TV images show smooth movement, even though they are composed of a sequence of still images, but when presented at the rate of 25fps the eye cannot see the gaps in between. With the waterfall, go further still and at 1/2sec the water stream will begin to look quite surreal and more like clouds than water. You will need a tripod to use long shutter speeds like this.
You can also deliberately introduce blur to emphasise the impression of speed and movement with a popular technique known as panning. Panning is when you move the camera to follow the subject, often using a mid range shutter speed like 1/125sec or 1/60sec. The subject should remain relatively static in your viewfinder as you track it, but the background is rushing past in a blur emphasised by the slightly longer shutter speed. Not only is the impression of speed enhanced, but the blurring of the background makes the main subject stand out more. Panning is a great technique, but needs practise. The secret is smooth and accurate tracking of the subject, but even the experts will take two or three shots if possible. A monopod is a very useful accessory to help give your panning skills a boost.
It is not only the subject that is likely to move in your pictures, so will the camera unless it is bolted down to a heavy tripod. Camera shake is the result of trying to hand-hold the camera when using a shutter speed that is too long. Camera shake is very common, and while it is often obvious, more often it is not so obvious but just takes the edge off a nice sharp picture. You might blame the lens, or poor focusing, but it’s just as likely to be your unsteady hand.
Using telephoto lenses emphasises camera movement, in the same way that it can sometimes be hard to hold a pair of binoculars absolutely steady. There is a popular rule of thumb that can help you judge the slowest shutter speed that you can use with confidence, and that is the shutter speed should never be slower than the focal length of the lens, so if you use a 200mm lens, don’t go slower than 1/200sec. However, this old rule must be qualified, corrected, and taken with a large pinch of salt.
To start with, this guide only applies to FF-35mm cameras and because the effective focal length is increased by the crop factor on most D-SLRs, the new 35mm equivalent focal length must be used. So on a Canon D-SLR with a 1.6x crop factor, 200mm becomes 320mm, and therefore your slowest shutter speed should be 1/320sec.
But even more importantly, you, the photographer, must also be figured into the equation. Nobody’s hands are the same, and how steadily you can hold the camera will also depend on the picture-taking situation. Are you standing upright, relaxed and leaning against a wall for extra support, while holding the camera tight to your chest? Or are you down on one knee, and stretching uncomfortably to get just the view you want? The difference between these two examples in terms of the shutter speed you need to guarantee a sharp result will be at least two stops (to use the photographers’ jargon) so that 1/320sec needs to be raised to 1/1250sec in the latter circumstances.
One of the best experiments you can ever do, that will only take an hour or so but will benefit every picture you will ever shoot from now on, is to take a series of test pictures with different focal length lenses and in different shooting positions, and compare the results. You will need a tripod in order to get a perfectly sharp image to compare your hand-held shots against. Choose a distant subject so that there’s no danger of inaccurate focus affecting the results and run through as many different shutter speeds as you can, with as many different lens focal lengths as you’ve got, and in various shooting positions. Take several pictures each time. With digital, it is so easy to do this and blow them up on your PC monitor to see just how steady you actually are, compared to the tripod images, and draw up your own personal hand holding formula.
When you’ve done this, you’ll be pleasantly surprised that with wide angle lenses, you can often hold the camera steadily enough to use quite long shutter speeds. The benefits of this are obvious in terms of the exposure settings and the depth of field options it gives you. Wouldn’t it be wonderful if you could get away with using longer shutter speeds all the time? Well, now you can, and without using a tripod.
There is new technology available that has a dramatic effect on steadying your shaky hands. Canon call it Image Stabilization (IS), Nikon call it Vibration Reduction (VR) and most manufacturers offer something similar. They all use movement detectors coupled to electronically driven optical devices that cancel out camera shake significantly. Canon claims its IS system allows you to shoot at shutter speeds up to three stops longer than would normally be possible. That’s the difference between 1/500sec and 1/60sec - quite a claim, but it is true. There’s only one caveat, and that is if you need 1/500sec to freeze action, then shooting at 1/60sec with IS is still going to give you a blurred subject. Nevertheless, this is a major and extremely practical technological breakthrough, and even the extra cost is reasonable.
Automatic exposure modes
All D-SLRs have a wide range of exposure control options which provide endless creative permutations to explore. They range from fully Manual operation (M) where every control setting is made by you, through semi automatic where you make the main choices and the camera does the rest, and on to fully automatic Program (P) where all you have to do is point and shoot.
There will also be a selection of Basic Exposure Modes, which are marked with a symbol depicting popular subjects like action, or a portrait or landscape, and so on. These modes will set the exposure fully automatically, but will also bias the shutter speed and lens aperture selection to give the best pre-programmed result for the type of subject you’ve selected.
For example, if you select the action symbol, the camera will always try to use the fastest shutter speed it can, according to the brightness of the light available. For a portrait, it will assume you want shallow depth of field and will chose a wide lens aperture, and for landscapes it will go for maximum depth of field, so setting a small lens aperture.
Clever stuff? Well, yes and no.
For action photography, you will often want a fast shutter speed to freeze movement, but not if you’re panning and want a slower speed to help blur the background. For a close-up portrait, you would usually go for a wide lens aperture for shallow depth of field, but if you want to show some of the background to illustrate the subject’s environment, you would probably opt for a smaller lens aperture and zoom back for a wider view.
In situations like these, the semi-automatic modes can be very useful. There are two, marked Tv (Time value) and Av (Aperture value). With Tv, you set the shutter speed you want and the camera will automatically match it with the correct lens aperture. It will also vary the aperture if the light changes while you’re busy concentrating, so that’s one thing less to worry about. Setting Av does the same thing, but in reverse of course, after you have selected the lens aperture.
How many pixels do you need?
Pixels were once the be-all and end-all of any digital decision, but it has now reached a stage where the sharpness of digital pictures is often higher than you can even see or print. The quality of film, supreme for over a century, is now beaten and chasing ever-higher pixel counts needs to be considered in context. For example, if you never make prints larger than 6 x 4in, then, believe it or not, anything more than 2m pixels is wasted - printers cannot reproduce any finer detail, and unless you squint and look very closely, you can’t see it, either! Be wary of trying to measure a camera’s pixels-per-inch count (PPI) against the dots-per-inch (DPI) of a printer as printers use several dots to reproduce one pixel, depending on the colour, so comparisons are difficult.
Moving up to A4 prints – the size of a full magazine page - requires no more than 5m pixels maximum. In practise, you can get very high quality prints of this size from a camera with less pixels, mainly because larger prints are always viewed from a little further away, and clever image enhancement software can make a big difference.
But having said that, it is always nice to have a little more resolving power in hand, a few more pixels, for big enlargements and for zooming-in at the printing stage to get the best composition, but without losing sharpness. Just bear in mind that it’s not only pixels that matter and at larger print sizes, it is quite likely that the resolving power of the lens (its ability to show fine detail) will also be exceeded in some situations, or that your focusing accuracy will be slightly out, or that the image will be degraded by camera shake. So, if you are seeking ultimate image quality, in addition to pixels you must also ensure that your lenses are the best available, that you have a high quality photo printer using six or more inks (not just four) and that you always use the highest quality printing paper. Last but certainly not least, your photographic and digital processing techniques have got to be absolutely impeccable.
JPEG and RAW images
D-SLRs are mini computers that contain sophisticated image processing software to help you get the best quality photos. The two most popular types of image file are JPEG (Joint Photographic Experts Group) and RAW (which just means unprocessed).
JPEG processing is a universal standard that both enhances and compresses image files, and it works very well. Unless you intend to spend time post-processing with specialist software like Photoshop, JPEG is the one to use. You can select different standards of JPEG compression, and at the highest quality settings it is almost impossible to detect, but the big bonus is substantially reduced file sizes – you can get hundreds of pictures on to a 1Gb memory card. The camera can also handle these smaller files much more easily, so if you are shooting fast action at maybe 5fps, the camera will keep going longer before the buffer is filled and you are forced to stop for a few seconds while data is transferred to the memory card.
You can also customise JPEG processing by adjusting sharpness, contrast, saturation and colour tone levels in the camera to get just the kind of photos you like. The camera’s default settings are usually a good starting point, but to see the effect these adjustments to levels make, do some test prints and compare. It’s similar to adjusting the picture settings on your TV, but bear in mind that what comes out of the camera might not look exactly the same on your PC monitor, and may be slightly changed again by your printer. This is not a fault and it is possible to get all your devices calibrated together, but you can usually fix things yourself with a few simple adjustments.
RAW is for experienced users who want the absolute maximum quality possible and are prepared to put the work in to get it. RAW is the digital equivalent of the film negative and takes the whole image file from the sensor and records it on the memory card without any compression by the camera. Unprocessed RAW images often don’t look their best, so you must post-process them with a PC and software, but then you will be rewarded with outstanding results.
Some cameras allow you to shoot both RAW files and JPEGs simultaneously, giving you the best of both worlds, but RAW files are also huge. Their size varies according to the number of pixels but they are many times larger than JPEGs, and will fill up your memory card quickly.
Flash in daylight
Flash doesn’t have to be used at night – it can also produce wonderful pictures in daylight. The technique is called fill-in flash, when the flash is used to fill-in dark areas of shadow. It works particularly well for portraits.
If your subject is facing the sun, they will squint and look uncomfortable. So turn them around, so that the light is shining from the side or from behind. With the sun in their hair, they’ll look great (girls, guys, kids - it doesn’t matter). But now the face will be in shadow and if you make a normal exposure, the camera will see lots of bright light that will lead to under exposure of the face. That will give you a silhouette.
You now have two options to correct this: firstly, you could dial in some plus exposure compensation, which will lighten the face, but will bleach the bright background into pure white. Ideally, what you want is to balance the attractive bright light coming from behind with more light from the front. You could do this with a reflector, but they are big, cumbersome, and tend to get blown away (literally!), so your second easy option is to use fill-in flash. Fortunately, fill-in doesn’t need much power so the built-in flash will be fine, and the camera will do all the exposure calculations for you, to ensure a good balance between the daylight and flash. It will also prevent you from using a shutter speed faster than the x-sync speed, lest you forget. Easy, and it looks great with the flash also putting a nice highlight in the eyes.
Flash at night
When the sun goes down, a lot of easy picture taking opportunity goes with it. Artificial light, from either ordinary light bulbs or fluorescent tubes, is much less bright than sunlight and even though you can see perfectly well, your camera cannot do the same Also, most kinds of artificial light are not the same colour as daylight, and you should adjust your camera’s white balance control to get natural looking pictures. But don’t give up – you just need to try a little harder. Crank up the ISO, open the lens to its largest aperture, use the IS or VR feature if you have it, and hone your technique with careful focusing and a steady hand. Your reward will be photos full of natural atmosphere.
Or you can use flash. While flash is no substitute for daylight, if you understand its strengths and weaknesses, you can adapt to its limitations and get some great pictures.
Red-eye is a common problem, so common that there are several tricks that camera makers use to get rid of it. None of them works very well, although many software programmes can detect and eliminate it quite effectively in post-processing. But it’s much better to avoid it in the first place.
Red-eye is caused by light from the flash reflecting back off the retina of the eye, directly into the lens. It is worst when the distance between the flash head and camera lens is short, so moving the flash away from the lens is an instant cure. However, if the flash is built-in to the camera, this is obviously impossible and a good reason to buy a separate flashgun. This will have much more power and can be used in different positions and in various ways to greatly improve your flash photography.
Bounce flash is one technique that you can use with a more powerful gun, and it will eliminate red-eye, give soft natural looking light, and get you around a tricky bit of physics called the inverse square law.
The inverse square law simply means that if you double the distance from the flash to the subject, the light is reduced to one quarter. Try it yourself by pointing a torch at a plain wall and measure the circle of light. Move back to double the distance and when you measure it again, the circle of light will be four times the area and so also a quarter of the brightness.
Here’s a familiar example where the inverse square law explains those horrible snaps we’ve all taken at parties where someone’s face close to the camera is bleached ghostly white, while other people just a few feet away are almost too dark to recognise. Here’s why – if the nearest person was two feet from the flash, then people four feet away will be lit by only one quarter of the light, and eight feet away the light is reduced to one sixteenth. That is far too great a range of brightness and the solution is firstly to move back so that the greater distance reduces the rate at which the light diminishes, then try and arrange your picture so that all important areas are roughly the same distance from the flash. Finally, point the flashgun at a white ceiling and it will flood the room with light as the flash bounces off the ceiling and down again. It’s a really easy technique as all the complex exposure calculations are handled by the camera. The only problem may be a lack of flash power – bounce flash just gobbles light, so always buy the most powerful flashgun you can.
Composition
This is a controversial topic, where rules are often best when broken, so we’ll stick to some simple basics. Perhaps the best advice on composition is to stop, look and think. Now read that again, slowly. Take your time, and then choose your moment. Don’t just pick up the camera, zoom in and fire off a few frames in the hope that one will be good. Chances are that it won’t.
If you can, walk around your subject, seek out interesting angles, and if you have an eye for a picture (and most people do) very often things will click into place, the composition will work and the picture will look balanced.
And when the picture does look right and well balanced, you’ll usually find that key areas of interest correspond with the Rule of Thirds. It works like this. Imagine a rectangle, say 6 x 9 inches. Along the 9in side, measure 3in from the edge and draw a line to the opposite side, move along another 3in and draw another line. Now move to the shorter side, measure 2in in and draw a line across, then move another 2in and do the same again.
Your basic rectangle will now be divided into nine smaller rectangles, and the lines will intersect at four points around the centre of the frame. These four points, each one a third in from the outside edge, are the points referred to in the Rule of Thirds where the eye tends to rest naturally when viewing an image. A simple test – imagine this template and overlay it mentally onto pictures that you like. You will be surprised how often keys areas of interest fall on one or more of the Thirds. It’s almost spooky.
A simpler way of putting it is to avoid putting key elements of the picture either right in the middle or close to the edges of the picture, but this is a little at odds with another good phrase to remember when composing your picture – Fill the Frame for Impact. For maximum punch, cut out all unnecessary detail, move in as close as you dare (and then a little more) and place your subject bang in the centre. It’s something of a shock tactic, but with the right subject, it is very powerful.
One more thing – lead in lines. These are often the key to great landscape pictures where the foreground sometimes adds nothing to the image and can even distract from the great view beyond. So look for a lead in line, often a road, river, a fence or wall, that attracts attention and then directs your eye from the edge and into the heart of the picture towards the centre of interest. This is hard (unless you have a portable wall to hand!) but when it works, it really makes the picture.
- JamieFRST
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