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DPChallenge Forums >> Hardware and Software >> EF-s 10-22 -> When 3.5 vs. 4.0 vs. 4.5?
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 01/15/2006 01:44:10 AM · #1
Cannot seem to find where this lens changes max app. Does anybody know the cut off points in mm?
 01/15/2006 01:55:06 AM · #2
It's continuous. The physical diameter of the max aperture is constant, and as the zoom extends it becomes a smaller f/stop. This is because f/stop is defined as the ratio between physical diameter of the aperture and focal length of the lens. 25mm aperture on 50mm lens is f/2.0, 25mm aperture on 100mm lens is f/4.0...

R.

Message edited by author 2006-01-15 02:07:38.
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