Photons Missing In Action

Started Nov 24, 2009 | Discussions thread
OP Marianne Oelund Veteran Member • Posts: 7,765
Unworkable in Practice

noirdesir wrote:

Just to make sure we are talking about the same thing, I meant that if a f/2 lens actually was an f/2.1 lens and you tried to measure the accuracy of f/2.8 stop you would measure a delta of 0.8 stops between them or in other words conclude that the f/2.8 aperture is 1/5 stop too bright (always assuming naturally that the ratio between f and t-stop is the same for both apertures which is what you assumed already). Now, if the camera knew that a lens actually had a f/2.1 aperture wide open it would adjust a nominal f/2 and 1/100 s not to f/2.8 and 1/50 s but to 1/56 s (eg, in aperture-priority mode).

Using the lens CPU in such a scheme would require that the lens behavior be consistent. However, it is variable from camera to camera - and this is why I am urging users to test their own equipment.

This is all a matter of some very small mechanical misalignments. The movement of the camera's aperture control lever is only about 0.8mm per stop, or less than 0.3mm per 1/3 stop increment.

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