Digital.Camera.Magazine.Complete.Photography.Guide.Mastering.Exposure (pdf document) download at fliiby.com

"Complete photography guide Exposure TAKE STUNNING PHOTOS USING OUR EXPERT TIPS ■ How to read a histogram ■ Metering for different tones ■ Coping with unusual lighting Master VITAL SKILLS GUIDE Exposure Trying to get the ‘correct’ exposure is one of the greatest challenges for those beginning in photography. But it needn’t be. This book will show you the pitfalls to avoid, when to alter your camera’s settings (and by how much) and how to get creative with metering. Exposure 3 Master Exposure TAKE STUNNING PHOTOS USING OUR EXPERT TIPS Master Contents ■ Exposure basics ■ Adjusting exposure ■ When things get tricky ■ Master of exposure: Ansel Adams ■ Background problems ■ Unusual lighting ■ Master of exposure: Galen Rowell ■ How to read a histogram ■ Controlling the dynamic range ■ Using a neutral density grad ■ Master of exposure: Pål Hermansen ■ Low light exposures ■ High key/low key ■ Top 10 tips p10 p14 p16 p20 p22 p26 p30 p32 p36 p38 p42 p44 p46 p49 Exposure 7 Use your grey matter he biggest advantage digital has over ﬁlm is the fact that you can check your shot once you’ve taken it. You can bring up a histogram to check the brightness range of a scene – and make sure you’re not underexposing or overexposing it. You can, if your camera allows, switch on a ﬂashing highlight to show you any blown highlights where detail will be lost in your photograph. You can then change your exposure accordingly. And if all that fails to produce the balanced exposure you want, you can go some way to rectifying it while image-editing. It is, however good to get things right ﬁrst time – to produce a high-quality image in-camera which you only have to do minimal tweaking with later. This book arms you with practical advice for getting the exposures you want, and the conﬁdence to take control when the camera’s being fooled. We’ve got clear examples of when this can happen and what you should do. We also show you the inspiring work of three master photographers to give you an idea of you what can be achieved once you’ve nailed the basics – which start on page 10… T Marcus Hawkins Editor, Digital Camera Magazine 8 Exposure Exposure basics n the face of it, exposure seems a pretty straightforward business. In order to produce a good range of tones in your picture, the camera has to make sure the right amount of light reaches the sensor. And it does this (or you do) by adjusting the length of the exposure (the shutter speed) and the light intensity (the lens aperture). The image is formed by the accumulation of light on the sensor during the exposure. All digital cameras incorporate exposure systems which will do this automatically, so what’s the problem? Even the most sophisticated metering system is unable to understand what the camera’s looking at, or what the photographer’s intentions might be. This is where you need to take control. O 10 Exposure Digital’s dynamic range Cameras will struggle to deal with scenes where there’s an extreme brightness range. With ﬁlm, this is called ‘exposure latitude’, with digital cameras it’s called ‘dynamic’ range. On a very bright sunny day, it may be impossible to ﬁnd an exposure which records some detail in the shadows without ‘blowing out’ the highlights, or vice versa. It’s generally agreed that digital cameras have a similar exposure latitude to slide ﬁlm, and you can start off by assuming a dynamic range of about 4 EV values. This means you should still be able to see or recover useful shadow detail 2 EV darker than the mid-tones in your image, and highlights 2 EV brighter than this mid-tone value should record well too. So what do you do if the brightness range in the scene exceeds this 4 EV range? There are ways of dealing with this, and we look at these a little later on. Mid-tones The idea of ‘mid-tones’ is important in exposure. On one level, it describes areas of the scene which are more or less in the middle of the tonal range. You might say these are the parts you want to expose correctly. But how dark or light are these mid-tones? In order to work out the exposure, your camera has to work to a standardised average ‘grey’ tone – 18% grey, to be precise – and try to adjust the exposure to reproduce your subject with this level of brightness. This is one of the principle drawbacks of all built-in camera meters, no matter how sophisticated. They don’t know what it is they’re looking at, and what intrinsic tone the subject ought to have. All subjects will be reproduced to this 18% grey value, which is a problem we’ll come on to shortly. At ﬁrst glance, this scene seems to average out an overall mid-tone. However, the bright wall of the cottage is overexposed. Dialling in some underexposure would take the edge off this, at the expense of detail in the shadows. Exposure 11 Metering patterns Light meters may not be able to understand that different subjects may have different intrinsic brightness levels, but camera makers have at least been able to allow for difﬁcult and contrasty lighting conditions. By default, digital cameras use ‘multi-pattern’ metering systems that measure the light values at numerous points in the scene. This helps them build up a picture of the type of lighting you’re shooting in, and the camera may adapt automatically to backlighting, for example. Multi-pattern metering systems are hard to second-guess, though, and many photographers prefer simpler ‘centre-weighted’ metering, which averages the whole scene but places extra emphasis on the central area. Spot metering is very specialised. It takes a reading from a very small area of the scene only. Aperture and shutter speed Digital cameras control exposure using both shutter speed and aperture. Why both? Wouldn’t one or the other do the job? There are creative advantages to these two means of exposure control. Smaller lens apertures offer more depth of ﬁeld (near-to-far sharpness), while fast shutter speeds let you freeze fast-moving objects. Shutter speed and aperture are interchangeable, so that if you want to use a smaller lens aperture, you can compensate with a longer exposure. Or, if you want a shorter exposure, you simply set a wider lens aperture. For example, if your camera indicates an exposure of 1/250sec at f/8 but you want to shoot at 1/1000sec, which is two stops, or EV values, faster, you need to increase the aperture value by two stops as well, to f/4. Some cameras allow you to adjust shutter speed and aperture values in 0.3 EV steps, but the same principle applies – a change in one must be mirrored with a same-sized change in the other. To blur the crashing waves in this scene, a smaller lens aperture has been selected in order to obtain a slow shutter speed. When faced by a mid-tone scene such as this, multi-pattern metering systems can be trusted to produce wellexposed photographs. 12 Exposure Exposure 13 Adjusting exposure S o how precise do you have to be with exposure? Even though digital cameras only have a certain amount of ‘exposure latitude’, in practice there are many different ways of interpreting a scene, and many exposure errors can be rectiﬁed or at least improved with a bit of image-editing. To give you an idea of how the subject brightness changes with exposure, here’s the same scene at seven different exposure values, all shot at the same lens aperture, but with shutter speeds 0.5 EV apart. These also demonstrate the idea of exposure latitude and dynamic range. There isn’t one shot where detail’s been recorded both in the foreground and the garden outside – the scene is outside the dynamic range of the camera’s sensor. You might prefer the ‘overexposed’ shot because it shows the subject’s face with a nice high-key effect, or a darker silhouetted version. Or you might open one of the in-between shots in Photoshop and attempt to balance the tones more evenly. +1.5 EV The shot with the biggest increase in exposure works well – it ‘bleaches out’ a potentially distracting background. 14 Exposure +1 EV +0.5 EV 0 EV -0.5 EV -1 EV -1.5 EV Exposure 15 When things get tricky W e explained in the previous section that camera exposure systems could adapt to a degree to ‘difﬁcult’ lighting, but that they had no sense of the intrinsic lightness or darkness of speciﬁc subjects. But does this really make much difference? Indeed it does. If any of your digital camera shots come out badly exposed, it’s often the intrinsic brightness of the subject that’s caused the problem, not ‘difﬁcult’ lighting or any error on your part. Just to show you how much difference intrinsic subject brightness does make, we’ve arranged a series of still-life experiments… Metering for dark tones/black We used a black background for this shot of an ornamental elephant, which itself was a mixture of dark red and black. The camera didn’t know any of this, of course. All it could do was measure the amount of light it ‘saw’. Not surprisingly, this wasn’t very much! As a result, the camera increased the exposure. Remember, all it can do is attempt to render the subject as an overall 18% grey tone, because while you and I might realise the elephant and the background is black, the camera doesn’t have the cognitive powers of the human brain. It’s dark, increase the exposure. That’s the limit of its thinking. The result isn’t too hard to predict; an 18% grey elephant against an 18% grey background. No Adjustment The black background and dark subject fooled our camera’s meter. Left to its own devices, it overexposed by 2 EV. 16 Exposure -2 EV Watch out for highlights Our elephant shot reveals something else that’s interesting, too. In the overexposed version, look at the dried ﬂowers in the foreground. They’re actually close to an average 18% grey tone in real life, but because the camera’s increased the exposure, they’ve been almost completely burned out. However, by manually overriding the exposure and reducing it by 2 EV, we’ve not only restored the elephant and the background to a ‘proper’ black, we’ve restored the correct tones to the dried ﬂowers. The same will apply if you’re photographing black birds with bright beaks, for example. When you’re photographing dark-toned subjects, the camera will often increase the exposure and lose highlight detail in other parts of the scene. The subject’s darkness doesn’t have to be as extreme as that in our example. If you’re shooting dark-toned vegetation, for example, reducing the exposure by 0.7 EV to 1 EV is often a good idea to preserve the depth of colour and highlight detail. Exposure 17 Metering for light tones Unusually dark-toned subjects are not an everyday problem. Light-toned subjects are far more common, and they typically distort the camera’s meter reading to a greater degree. Our still life shot demonstrates this well. The ginger, onions and squash are all fairly light-toned, along with the cloth beneath them, but even so you might expect the camera to expose them correctly without any help. The result, though, is distinctly dull and gloomy. Only by reshooting with +0.3 EV compensation were we able to restore a realistic-looking brightness to the shot. At ﬁrst you might need to experiment a great deal to ﬁnd appropriate EV compensation values for light or dark-toned subjects. But with practice, and a growing understanding of your camera’s behaviour, it gets a lot easier to work out when to override the camera and how much by. No Adjustment +0.3 EV These vegetables are lighter-toned than the average 18% grey looked for by the camera’s meter, so we needed to apply EV compensation to make sure this is how they were reproduced. 18 Exposure No Adjustment +2 EV If you’re photographing anything white, beware! Your camera’s meter will attempt to reproduce it as a muddy grey, so you need to intervene. This shot required +2 EV exposure compensation to look ‘right’. Metering for white White subjects are a special case, and the cause of the most severe underexposure problems. They’re a special case because the world is full of white objects and backgrounds, and because you might be surprised at just how bright they are. This still life demonstrates this very well. Remember, we want objects to appear in photos as they do in real life, and not reduced to the 18% grey assumed by camera meters. Our ﬁrst attempt, shot using the camera’s default exposure reading, was a disaster. Indeed, the overall tones are very similar to those of the default black elephant shot, demonstrating how the camera attempts to reduce all tones to the same value. In order to reproduce the whiteness of our subject, we had to increase the exposure value by 2 EV. You’ll have to do the same with snow scenes, for example, or close-ups of wedding dresses. Exposure 19 Master of exposure Ansel Adams here can’t be many people who’ve never seen an Ansel Adams photograph. He is the acknowledged master of landscape photography. He achieved so much before his death in 1984 of heart failure at the age of 82. Adams was both a photographer and conservationist and started the f/64 group (an association of Californian photographers who promoted ‘pure’ photography) with Edward Weston in 1932. He’s perhaps better known for developing the ‘zone’ system for exposure, a technique which enabled him to visualise how he would print the various parts of the image, and expose the negative accordingly. The tonal range he managed to extract from his black and white ﬁlm was simply incredible. T 20 Exposure This is unmistakably an Ansel Adams landscape. The richness, depth and detail is astounding, the exposure capturing every nuance of light. It pictures the Tetons and Snake River in Grand Teton National Park, Wyoming, and was shot in 1942. To learn more about Ansel Adams, pay a visit to anseladams.com. Exposure 21 © Corbis Background problems t’s not necessarily the subject of your photograph that can give you exposure headaches. The tone of the background is just as important, and can have a big inﬂuence on the exposure reading. Even if your subject consists of fairly even mid-tones, an unusually light or dark-toned background can produce exposure errors. The size of this error will depend on how much of the frame is taken up by the background. It can also be hard to I judge exactly how much emphasis the camera is giving to the subject itself, since multipattern metering systems may concentrate on the object in the middle of the frame, which may or may not be where your subject is. Size matters This shot uses a mid-tone subject set against a dark background, but shot at two different zoom settings, so that in one the onions and ginger take up nearly all of the frame, while in the other they’re quite small relative to the background. In both cases the camera’s default auto-exposure readings were used. The close-up shot is correctly exposed, but in the zoomed-out version, the larger proportion of dark background has fooled the camera into overexposing by 1.3 EV. We tried the same experiment using a light background. By zooming right in on the You may not encounter completely black backgrounds like this when you’re out shooting, but dark tones will have the same effect. Light backgrounds cause mid-toned subjects to underexpose if they’re not big in the frame. Bear this in mind when framing people against pale skies. 22 Exposure artiﬁcial fruit, we’ve excluded nearly all of the background, and the resulting exposure is pretty well spot-on. When we zoomed out, though, the proportion of the frame taken up by the background was far higher, leading the camera to reduce the exposure by 1.3 EV, which has left the shot underexposed. The degree to which the background inﬂuences exposure will depend on the amount of the frame it takes up and its brightness, but it can make a big difference. Exposure 23 Complimentary tones Here’s another experiment showing how the exposure changes when you place a dark subject against a light background. In this case the best exposure is the middle one, because the light background has reduced the exposure. This helps render the dark tones of the lenses more accurately. You can also see what happens when you place a light subject against a dark background. The results are similar. Close-up, the while ﬂowers and vase in our set-up cause the camera to underexpose. In the wideangle shot, the dark background has caused overexposure. The middle shot is the best because the tones average out well. 24 Exposure Exposure 25 Unusual lighting J ust to make life that little bit more awkward, it’s often the most dramatic and ‘difﬁcult’ lighting that makes the most exciting photographs. You face two challenges here. The ﬁrst is that the brightness range of the lighting will often exceed the dynamic range of your camera’s sensor, so you have to decide which is the most important part of the scene and base the exposure on that, leaving extreme highlight or shadow detail to disappear. Once you’ve done that, you need to work out how to take an exposure reading that will render the important part of the scene properly. Backlit images can be some of the most exciting, but they also provide plenty of exposure headaches. Most compact digital cameras will favour shadowed foreground subjects, like our pedestrians, and this compromise has worked out well here. 26 Exposure Backlit subjects With backlit subjects, the light’s coming from behind your subject and towards the camera. This means that the side of the subject facing you is in shadow against a bright background. It’s unlikely that your camera will be able to record detail in the subject and a full range of tones in the bright background too, so you’ve got a decision to make. You can expose the shot to get detail in your subject, and render the background as a brilliant, ethereal white, or go for a silhouette effect, as you might with a dramatic sunset, for example. In both cases, spot metering can be the most reliable solution because multi-pattern metering systems can behave a little unpredictably. Some are designed to give priority to subjects in the centre of the frame, especially with the tonal distribution characteristic of backlighting (the camera can detect this). You may get a properly exposed subject when you wanted a silhouette, and vice versa. Exposure 27 Sidelit subjects Sidelighting is less difﬁcult to deal with. The overall contrast tends to be lower because you’re not shooting into the light. However, the long shadows cast by the light can inﬂuence the meter in ways you don’t want. Digital cameras, especially non-SLR models, seem to favour shadows over highlights in a scene, so you can often end up with an overexposed image with ‘blown’ highlights and shadow detail that’s too light. The strong, textural quality of sidelighting, however, relies heavily on deep shadows and richly-coloured highlights. It’s a good idea with sidelit subjects to at least bracket your exposures, or take one at the default meter reading and then another with -0.3 EV or -0.6 EV compensation. With digital cameras, a little underexposure is a lot easier to correct later than overexposure. Blown highlights are lost for good, but you can often extract an amazing amount of colour and detail from gloomy shadows. If you want to capture the full richness of colour and textural quality of sidelit subjects, you may have to manually reduce the exposure to retain those dark shadows. 28 Exposure Spotlit subjects Spotlit subjects are particularly difﬁcult to deal with. The situation here is comparable to that we set up when photographing subjects against a dark background, but the con..."

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