Lens used on digital SLR vs Film SLR

[Lozlo]

Does anybody know if the focal length of any given lens differs when used on a digital SLR, like the Nikon D100 for example, and a film SLR, like a Nikon N80 for example?

Thanks and happy new year to all,
David.

[shene]

Originally Posted by Lozlo

Does anybody know if the focal length of any given lens differs when used on a digital SLR, like the Nikon D100 for example, and a film SLR, like a Nikon N80 for example?

The focal length of a lens is fixed when it is produced. Thus, mounting a lens on D100, N80 or whatever Nikon SLR/DSLR will not change its focal length. However, since the D100 uses a smaller APS size sensor, it only see a portion of the image delivered by the lens and hence reduces the angle of view. In this way, the conceptual focal length calculated from thins changed angle of view changes as well, which is 1.5 times of the lens. However, this does not change the focal length of the lens. For example, mounting a 50mm lens on a N80, you will see the angle of view delivered by the 50mm lens. If this 50mm lens is mounted on a D100, since the sensor only "sees" a portion of the image circle of the 50mm lens, the angle of view is reduced and focal length is increased (in the sense of the sensor). The increment is 1.5 times, which means the 50mm lens becomes a 1.5*50=75mm on a D100. But, the focal length of the 50mm lens is still 50mm!

CK
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