chapter
Conversion Factor
Pages 1

First we should discuss Conversion Factor, also called Crop Factor and Focal Length Multiplier (FLM), and what it means. The sensor in the Sony A200 is smaller than that of a 35 mm camera, so lenses have a different field of view than they have on a 35 mm camera. To get the equivalent, just multiply the focal length of the lens you have mounted by 1.5. The focal length of the lens is always the same, regardless of the sensor or film size, but the reason we bother with a conversion factor is partly historical and partly thanks to the many sensor sizes on the market. Most of us who have taken pictures with a 35 mm film camera are familiar with how our various lenses performed at that film size. A 28 mm lens, for example, was a good basic wide-angle lens for most common landscape and tight photographic situations. But attach that same lens to most modern digital SLRs and it no longer looks so wide. The smaller sensor in the Sony A200 crops the image that the lens produces, so that it performs like a 42 mm lens would on a 35 mm camera. Feel free to ignore the conversion factor if you don’t have the history that tells you what a 28 mm lens should look like, because the new 28 mm on most digital SLRs is 18.6 mm; your A200’s kit lens is capable of zooming to 18 mm, or the equivalent of a 27 mm lens. For reference, the 18-70 mm kit lens is equivalent to a 27-105 mm lens on a 35 mm camera.