Consumer photographic lenses are almost always sold by their focal length when used on a 35mm camera (or full-frame professional DSLR). It’s already confusing enough to work out what their effective focal length is when used on an APS-C sensor (most consumer DSLRs), but since I’ve been getting into medium-format photography it’s even more confusing to work out what each focal length does what on which camera.
So I’ve done a little research, and prepared a table. I’ve included data for five “common” photography formats with their crop factors. The numbers are the approximate focal lengths in millimetres. Of course the boundaries for each category of lens are rather woolly at best.
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