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Old May 1, 2007, 4:21 AM   #1
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Is there a way to work out the equivalent optical zoom (ex 3x zoom), of a 200mm lens? Thanks
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Old May 1, 2007, 5:49 AM   #2
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If it's a 200mm lens, it isn't a zoom. If you're looking for equivalent magnification, so to speak (like with binoculars), a 50mm lens (for 35mm film) is usually considered to be equivalent to the human eye in terms of magnification, so you could say that a 200mm lens on a film SLR is like a 4x scope.

Do not confuse that with zoom range, though. A "4x zoom" only means that the focal length at full tele is 4x the focal length of that same lens at full wide angle.

To use my own camera as an example, the lens is a "10x zoom" with 35mm-equivalent focal length range of 38-380mm. Note that 380 is 10 times 38, hence "10x zoom." However, at full zoom, it's a 380mm lens; that gives a magnification of about 7.6x compared to the unaided eye. (At full wide angle, it's a 38mm equivalent, which has a "magnification" of 0.76x.)
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Old May 1, 2007, 6:28 AM   #3
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"x" zoom designations are useless marketing terms. As was mentioned, the "x" only refers to the greatest focal length divided by the shortest focal length. So for example, an 18-70 is almost a 4x but a 100-300 is only 3x, and a 200-400 is 2x. Obviously a 200-400 will give you alot more reach than an 18-70, but you wouldn't think so if just comparing "x". When looking at and comparing lenses, pay attention to actual focal length, not the "x" number.
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