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12-26-2011, 12:01 PM   #1
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DSLR & aperture lever arm

As I understand it, the Pentax DSLRs don't use the aperture lever arm on K & M series lenses because there is not a data pin on the lens to communicate with the body, is this correct? I think I know the answer but saw something on the forum here that made me second guess it.

12-26-2011, 12:04 PM   #2
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They use the flappy one that sticks out to actually stop the lens down, but not the one that moves together with the aperture ring that told older cameras what it's set to.

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12-26-2011, 12:18 PM   #3
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A-type lenses and newer encode their aperture range in the connection pattern of (most of) the electrical contacts, also with them the relationship to aperture opening / lever movement was changed from what it was with K/M-lenses. The latter has been kept same since. Hence, the bodies can fully control the aperture from A-series forward: they keep the lens fully open for a bright viewfinder and stop down to what is set on the body for exposure (provided that the aperture ring is in the 'A' position, one of the contacts is dedicated for this). The body gets further information via the data pin, but it is not needed for aperture control.



Last edited by jolepp; 12-27-2011 at 04:47 AM. Reason: clarification + links
12-26-2011, 12:56 PM   #4
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If the lens does not have the automatic "A" position on the aperture ring, you must set the camera to be able to control the aperture in the menu system. Then it will stop the aperture down, but only in M - manual - exposure mode. To get the camera to select an aperture in manual mode, you press the green button (AE/L on some models I think). This will cause the camera to stop the lens down, take an exposure reading, set the shutter speed and open the aperture for focusing. There is no need to do this for every shot you take - the camera will remember the last setting for you. A more detailed description is in a sticky at the top of the beginners' forum.


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