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Old Jul 29, 2011, 4:20 PM   #1
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I'm still learning my A200 and know that on at least some lenses, the stated focal length is lengthened, if you will because of the APS sensor. Is this true with all lenses or just those designed for full frame camera? How do I know the difference?
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Old Jul 29, 2011, 4:40 PM   #2
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"Focal Length" is a physical property of a lens, and does not change with the body it's mounted on. 'Full Frame' dSLRs have the same angle of view as 35mm film SLRs when using a lens of the same focal length, but 'APS-C' dSLRs (like your A200) have an image sensor that's 1/3 smaller than a standard 35mm film exposure, so when using a lens of the same focal length as a 'Full Frame' dSLR, it's angle of view is 1/3 narrower. In effect, a lens on an APS-C dSLR has an angle of view that's the same as a lens that's 50% longer on a 'Full Frame' dSLR. That is, a 50mm lens on your A200 has the same angle of view as a 75mm lens on an A900. This is referred to as "Crop Factor', and is only useful when moving between two worlds. If all you've got is an APS-C dSLR, it doesn't mean anything to you.
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  • 'Full Frame' is the new 'Medium Format'.
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