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Old Aug 24, 2007, 3:55 PM   #1
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What is the 1/2.5" CCD digital equivalent focal length and f-stop to match a film's field of view(zoom) and exposure value of a 50mm f/2.0 lens assuming same shutter speed and ISO ?


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Old Aug 24, 2007, 5:03 PM   #2
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itsme000 wrote:
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What is the 1/2.5" CCD digital equivalent focal length and f-stop to match a film's field of view(zoom) and exposure value of a 50mm f/2.0 lens assuming same shutter speed and ISO ?
First, aperture does not vary with focal length. In fact, aperture is a ratio of the diameter of the objective lens to it's focal length. So the aperture would still be f/2.0.

A50mm lens produces (about) a 40 degree angle of view on a 24mm by 36mm image sensor (in this case, a 35mm strip of film.)

Unfortunately,1/2.5" isn't specific enough to determinethe lens for an equivalent angle of view. A 1/2.5" image sensor could have a 3:2 aspect ratio (the same as for film), a 4:3 aspect ratio (conventional TVs and computer monitors),or a 16:9 aspect ratio (widescreen). In order to determine the focal length of a lens that would give a 40 degree angle of view, you'd have to know how wide the image sensor is, and that will change with each aspect ratio. (See http://en.wikipedia.org/wiki/Angle_of_view.)
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Old Aug 24, 2007, 11:38 PM   #3
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The crop factor of the 1/2.5" CCD is approximately 5.6, so the focal length equivalent would be about 9mm. As TCav mentions, exposure is based on the ratio, so that wouldn't change. The actual diameter of the aperture, of course is smaller by the same factor.



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