Exploring Focal Lengths
Changing your focal length can do much more than simply give you a wider or more telephoto shot
How much thought have you given to that lens on your camera? Most lenses today are zooms, and photographers use that zoom to get more or less of a scene, but your lens is capable of a lot more. Understanding lenses will help you better use any lens you own (even if it's the one permanently attached to your camera), as well as buy new ones as you need them.
The focal length of a lens refers to the distance between its optical center and the focal plane (the sensor in a digital camera) when it focuses at infinity; it's measured in millimeters (mm). More millimeters of focal length magnify the subject size, and as they increase, create a telephoto lens; fewer millimeters make the subject smaller, and as they decrease, give a wide-angle lens its focal length. Focal length, by itself, affects the size of a subject at the focus point, but has no relationship to the relative magnification of a subject within the picture area; you have to know the format or sensor size to determine that.
Most photographers first buy new lenses for the angle of view they get. In fact, the name "wide-angle" reflects angle of view ("telephoto" does not; it refers to a type of optical design). This can be an important consideration. You'll find a wide-angle lens useful to see more of a landscape or a town scene. A telephoto, with its narrow angle of view, will bring in distant subjects such as wildlife. Lenses, however, can do so much more for you.