this amount of underexposure can be corrected to almost normal.
CORRECT EXPOSURE
Here the correct exposure for this subject has provided detail from the darkest tones to the lightest highlights. Correct exposure is the ideal starting point to either use as it is or to add your own interpretation to on the computer.
OVEREXPOSURE
This picture is overexposed by +2 stops. Although it can be partially corrected later, the highlights, where they are pure white, will retain no detail as they are totally blown out and cannot be corrected.
HIGH KEY
The high-key effect is traditionally a black and white technique used for babies, children and glamorous women, giving a romantic interpretation of the subject. The lighting is as close to shadowless as possible. It is a good idea to have some small dark areas in the picture to contrast with the overall white tones. This baby picture is lit with soft overhead daylight that has eliminated most of the shadows, giving a soft, dreamy quality. It was overexposed by +1 stop to keep the highlights bright, using exposure compensation. 1/250 second at f5.6, 50mm, 400 ISO. GH
THE TECHNIQUE
The term ‘stop’ is used for referring to exposure. If you step up one stop you will halve the exposure, while if you step down you will double it. For instance, by moving the shutter speed up from 1/125 second to 1/250 second the exposure has halved (–1 stop). Moving down from 1/125 second to 1/60 second doubles the exposure (+1 stop). The same also applies to the aperture and ISO settings.
Your camera gives you the option of moving between stops in fractions of ⅓ or ½ of a stop. You will probably find that setting the camera to ½ step between the stops makes it a bit less confusing when using the shutter, aperture and ISO dials since it relates more easily to the doubling or halving effect of a whole stop.
LOW KEY
Traditionally used for masculine subjects to make a dark, moody interpretation, the low-key effect can be applied to many subjects. In this case the backlight encouraged me to underexpose the picture to get a dark, romantic feel, letting the backlight be used only to separate the lovers from the background. I used a 500mm mirror lens, which has made ‘doughnut rings’ out of the background highlights. I exposed for the highlights here, letting the shadows underexpose by –2 stops. 1/1000 second at f8, 500mm, 400 ISO. JG
UNDERSTANDING APERTURE
The aperture is one half of the exposure partnership. Together with the shutter, it controls how much light is exposed onto the sensor to form the image.
If you are new to using aperture and shutter speed controls, it’s a good idea to start with aperture priority (A or Av) mode. This will let you choose different apertures and you can watch the camera automatically select the shutter speed to produce a normal exposure. Find a subject with an object close to you in the foreground, one further away and another in the background. First shoot a picture of it with your widest aperture – f4.5, for instance – then stop down the aperture progressively to f16 for your next pictures. This will give you an illustration of how the aperture controls the depth of field – the amount of the subject that is in focus. Aperture is not only an exposure tool; the aperture we choose greatly affects our creative interpretation of the subject.
WIDE APERTURE
Here you can see a lens at its widest aperture – in this case f2.8.
NARROW APERTURE
Stopped down to f16, the aperture through which light passes is now greatly reduced.
SHALLOW DEPTH OF FIELD
To demonstrate the shallow depth of field that a standard lens will give when set at f2.8, I focused on the zebra. The animals in the foreground and background are out of focus, which has the effect of keeping our attention on the zebra.
WIDE DEPTH OF FIELD
This is exactly the same subject, photographed from the same distance, but stopping the aperture down to f16 has made everything sharp, from the cheetah in the foreground to the background tree. Every element in the picture is now vying for attention.
THE SHUTTER
The speed of the shutter is the other half of the exposure partnership, acting in tandem with the size of the aperture to control how much light reaches the sensor or film to form the image.
To get to grips with the function of the shutter, set your camera to shutter priority (S or Tv). The available shutter speeds will go from about 30 seconds to 1/4000 second. There is one more shutter setting, called Bulb (B), which can only be used when you are in manual mode (M). Here the shutter will stay open as long as the shutter release is kept pressed – a facility generally used for long night exposures.
Practise shooting at different shutter speeds, focusing on moving objects so that you can observe whether they are frozen in action or blurred. With speeds slower than about 1/60 second any camera movement will start to show as blur in the overall picture, so if you want sharp pictures at slow shutter speeds you will need to support the camera on a tripod or some object such as a wall or table. For hand-held telephoto lenses, assign a shutter speed that is at least as fast as the telephoto setting you are using – for example, a 200mm lens needs a speed of at least 1/200 second to avoid blur from camera movement. If you are using an APS-C sensor camera, you need to increase that to 1/300 second.
When you look at the photographs carefully afterwards, you will see that there is a considerable graphic difference between a picture in which a fast shutter speed has held hard-edged colour and shapes and one shot on a slow shutter speed, where the colour and shapes have become soft-edged.
FAST SHUTTER SPEED
The cyclist rode past the stationary camera, which was on a tripod. Exposure at 1/1000 second has frozen his movement.
SLOW SHUTTER SPEED
Here the exposure was 1/30 second as the cyclist rode past the stationary camera; the slow exposure has blurred the subject.
PANNING
Again the cyclist rode past and again the exposure was 1/30 second. This time the camera moved to follow his action, a technique known as panning. The result is that the cyclist is sharp and the background is blurred.
LENSES
The primary function of a lens is to focus the image onto the film or sensor. It also controls the angle of view and houses the aperture diaphragm.
You