Deciding which features you really need in a camera depends upon the type of pictures you expect to take. Here are some of the features you can expect to find on a DSLR and the purpose they serve.
Viewfinder: Allows you to look directly through-the-lens at your subject. On most DSLRs it provides useful information, such as aperture and shutter speed set, a flash ready light and under/over exposure warnings. By looking through the viewfinder you’ll see the focusing screen. In autofocus SLRs this shows one or more focusing ‘envelopes’ which should be aimed at your subject to achieve sharp focus.
LCD Panels: These are usually found on the top plate and the back of the camera and display all necessary information on exposure, film speed setting, AF mode, flash mode, etc. so you can find out at a glance what is happening.
Display Screen: Allows you to immediately review the image that you have just taken. In the good old days if film, you had to wait until the film had been developed until you saw the photograph.
Bulb Setting: Sometimes you may need to use a shutter speed outside the camera’s shutter speed range. The bulb setting makes this possible by allowing the shutter to be held open for as long as the shutter release is depressed. This should only be used with a cable release so as to prevent camera shake.
Depth-Of-Field Preview: Before pressing the shutter button, you can stop the lens down to the aperture you’re using so you can assess what is going to be in/out of focus in the final picture. It used to be a standard feature among SLRs, but is sadly missing from a lot of the basic SLRs. In stopping the aperture down, the image in the viewfinder will get progressively darker. If your aperture is set to say f/22 and you press the DOF preview button, the aperture will close and the image will be barely visible. A better alternative is to set the aperture at max, e.g. f/2.8 or f/4, press the DOF preview button to stop the aperture down (as the aperture is fully open, there will be no change in image brightness). You can then slowly adjust the aperture until you reach the desired setting. Using this method will give your eyes chance to become accustomed to the darkened image.
Exposure Compensation: Although camera meters are accurate and reliable most of the time, they can still be fooled by tricky lighting situations. For this reason the majority of cameras have some form of system that allows you to over-ride the meter and compensate the exposure to prevent error. If your scene has plenty of snow, the meter may under-expose by up to two stops so you might want to over expose by up to two stops.
Bracketing: Allows you to look take a series of images that vary in exposure, e.g. you could set the camera to take three images with say a 2 stop variation so your 3 photos would be (1) at 2 stops under exposed; (2) correctly exposed; (3) 2 stops over exposed. These photos could then be merged together for an HDR image or you could use one of them to achieve correct exposure.
Built-In-Flash: Some SLRs have a small flash unit built into the pentaprism that works in conjunction with the metering system to give perfectly exposed results. Integral flashguns are handy for taking snapshots indoors, or for fill-in flash, but the power output is low. They only work therefore on subjects relatively close to the camera.
Motordrive: This is a handy feature for ensuring you’ll (hopefully) never miss a shot and speed up the picture-taking process. Most work at a rate of three to five frames-per-second (fps), but some offer up to ten or beyond for the pro cameras. Once set, simply hold the shutter butter down and the camera will take a number of photos in quick succession. It is difficult to look through the viewfinder whilst this is taking place and you may fill the camera’s storage buffer if you take too many photos thus forcing you to wait until the camera has written the data to the storage card.
Multiple Exposure Facility: This feature allows you to take a second photo directly over the first image to create multiple exposures. A common feature on film cameras but rarely seen on DSLRs.
Eyesight Correction: Some SLRs have an adjustable viewfinder eyepiece that can be adapted to suit your eyesight. This is ideal if you wear glasses and prefer to remove them when taking photos. Other DSLRs allow a dioptre adaptor to be fitted to the viewfinder to perform the same function.