Single lens reflex SLR cameras

All SLR cameras have a clever optical system (as shown in Figure 8.7b), which allows you to view an image of the subject formed by the lens. It is a true 'what you see is what you get' (WYSIWYG) system. Unlike a compact camera, the shutter is not in the lens but in the back of the camera just in front of the film or sensor.

Looking into an eyepiece at the back of an SLR you observe a small, ground-glass focusing screen, onto which the scene is reflected by a mirror. So you see what the lens sees, and as you focus the lens it is easy to examine which parts of the subject are in focus and sharp and which areas are blurry. When you are satisfied that the picture is correctly composed, you press the shutter release button. The mirror then rises out of the way, blocking out the focusing screen briefly and allowing the image to reach the back of the camera, where the shutter opens to expose the sensor or film. As the distance from lens to film is the same as lens to screen (via the mirror), what was focused in the viewfinder will also be sharp on the film/sensor. In addition, because we view through the lens there is no viewfinder parallax error no matter how close the subject.

Since the shutter is at the back of the camera body, you can remove the lens and fit others of different focal length, even in the middle of a film roll or when the camera card is half empty. In fact, single lens reflexes are 'system cameras', meaning that the makers offer a wide variety of lenses and accessories, ranging from close-up rings (page 42) to special dedicated flashguns. So, starting off with a camera body and regular lens, you can gradually build up quite an elaborate camera outfit bit by bit as you become more experienced.

Cameras of SLR design include manual types, where you set most of the controls, automatic models that work with built-in programs and those that combine both systems. Both manual and automatic approaches have their advantages and limitations, so let's take a closer look at each design.

Figure 8.11 Fully manual SLR cameras provide the photographer complete control over all aspects of focus and exposure.
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