Choosing the right lens for your DSLR may turn out to be much more difficult – and more critical decision than buying the camera body itself. After all, a lens is a single most greatest factor that affects the picture quality.
Lens selection usually starts with deciding on a focal length. There are lot of names and numbers out there; wide-angle, macro, telephoto, normal, zoom, 18-55mm, 80-200mm 10-24mm, 50mm, blah, blah, blah… Adding to the confusion, for most digital SLRs, the focal length written on the lens barrel is not the actual focal length that your camera sees. Depending on the crop factor/sensor size of the camera, the focal length will vary. For example, a normal 50mm lens mounted on a typical Canon DSLR would have an effect of 80mm not 50mm (it would be 50mm if mounted on a 35mm film SLR or a ‘full-frame’ DSLR camera).
Rather than a lengthy explanation why this is, here’s a handy Focal Length Simulator that you might find helpful. You can choose different lens as well as camera body and mix and match to see how they affect the view angle. This simulator is provided by Nikon but the basic crop factor/focal length simulation applies to any brand.