- 1). Compare the sensors of the various models. If you will be using older lenses, a full-frame sensor model might suit you better, because this will ensure there is no cropping of the image because of lens compatibility. Also compare the megapixel count; this number will give an idea of how much an image can be enlarged. Professional users might look for a higher megapixel count than amateurs. More megapixels means an image can be cropped or zoomed more efficiently and with better results.
- 2). Examine the lens mount and compare the types of lenses each camera uses. Photographers who are migrating from a traditional film SLR camera might have lenses in their arsenal; many digital cameras allow for older lenses to be used on DSLR camera bodies. If you have lenses, make sure they mount on the DSLR body. If you do not have lenses, determine how easily lenses can be found and what they will cost. Having more lenses will give you greater artistic control as you progress.
- 3). Test the camera if possible and note the response time. See how quickly the camera turns on and off, how many shots can be fired and if there is any lag time while a file is being written to the memory media. This is particularly important if you are going to be shooting fast-action events, such as sporting events, or you will need to capture moments quickly. A slow camera means the moment may pass before the image can be captured.
- 4). Handle the camera bodies and note the location of the controls. Do you have to scroll through many menus to make changes, or are the controls clearly available on the body? Easy-to-reach controls are crucial for photographers interested in creative control or who are shooting in a fast-paced environment.
Source...