 Steven Chaitoff |
Aperture Construction Where is the aperture placed in most lenses? Closer to the front element or the rear? Also, why is it that the aperture's diameter is smaller than what it actually should be. For example, if you have a 50mm f/2, the hole inside typically doesn't measure even close to 25mm max. Likewise, a 600mm f/4 cannot possibly fit that kind of size...that's like a half foot opening! Where's the compensation for that? -Steven
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Jon Close |
For reasons similar to how a lens can have focal length 20mm when its rear-most element is over 40mm from the film plane. Lens focal length and aperture are stated in terms of a simple single element lens. But the actual construction of a modern 35mm camera lens can often involve as little as 4 to as many as 23 lens elements. The maximum aperture is limited by the diameter of the objective or front-most element. The diaphram is placed somewhere between the front-most and rear-most element, where the light has been refracted to a much narrower path. Here the diaphram closes down to a relative or equivalent aperture setting, not necessarily the diameter one would get by dividing the focal length by the f-number.
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