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12-02-2011, 03:11 PM   #1
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Pentax-A lenses - the essence of auto aperture

Hello.

Is putting A mode on the aperture ring the same as if I connected the flattened pin on the body to the M (or K or whatever manual) lens mount? I did so with my Revuenon 50mm 1.4 and the body recognized it as a lens with the aperture range from 1.2 to 22.

What is it all about then? Connecting just another pin to the lens and that's it? Is there any electronics in the A lens?.

12-02-2011, 03:20 PM   #2
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Lowell Goudge's Avatar

Join Date: Jan 2007
Location: Toronto
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There are some subtle differences

The A lenses have a linear change of aperture F Stops with movement of the lever, older lenses are generally area is linear, so the square of aperture. As a result while shortin the pin gives some appearance of control exposure is all over the place

Second the other pins code the max and min apertures so the camera can scale the movement properly.

The short answer is it can be made to "work" but it does so poorly
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