"Pretty much every compact digital camera on the market has a zoom lens, and of course there is a wide range of zoom lenses available for all digital SLRs, as well as a variety of non-zoom lenses with different focal lengths. A zoom lens is one that has a variable focal length. In this tutorial, we’ll take a look at what focal length means, and some of the effects you can achieve by varying it. The focal length of a lens is an expression of its magnification power, and is usually stated in millimetres. If you look on the front of your camera, usually inscribed around the front of the lens you’ll find the focal length range. (If it’s not there, take a look in your manual on the specifications page. It’ll be there somewhere.) For most 3x zoom digital compacts with 1/2.5in sensors the focal length range will be in the order of 5.8-17.4mm. Sometimes written next to this is the equivalent focal length on a 35mm camera. For 3x zooms this will usually be around 35-105mm."
This is a really nice article on details on what focal length is. I like the sample images that are presented, especially when the settings on focal length are provided.
Digital Photography Tutorial: Focal Length
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