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11-02-2010, 05:23 AM   #1
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"A" MF Lenses

I've picked up three A lenses to complement the two kit AF lenses I carried over from my film SLR. The question is; what are the orange colored buttons on the A lenses? They seem to not have any purpose and are not on my AF lenses.
Dudley

11-02-2010, 05:28 AM   #2
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what lenses are they.

Lenses with an A in the aperture ring are for automatic exposure modes. When in the A position the camera controls the aperture setting. and this allows matrix metering, P-TTL flash and auto exposure modes.

when the aperture ring is out of the A position, you need to have the function "Use Aperture Ring" enabled, and then the lenses can only meter in manual mode with the green button or equivelent
11-02-2010, 05:31 AM   #3
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They are just to provide a little extra grip when you are mounting/unmounting the lens.
11-02-2010, 05:33 AM   #4
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You press it to make it possible to move the aperture ring on or off the A setting. Your AF-lenses probably have the same button (unless they're FAJ or DA lenses), but without the colour.

This is of course assuming you're actually talking about a button, and not the index bump as boriscleto thinks.

11-02-2010, 05:46 AM   #5
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Boriscleto got it...I'm refering to the Orange button not the one to release the aperture ring. Thanks
11-02-2010, 06:12 AM   #6
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It's there to help you aligning the lens when you're going to mount it. So its purpose is similar to the red dot on the lens mount and the red dot on the mount plate (of camera body). But of course you don't align it directly to red dot on the camera mount plate. I don't have my lenses at the moment but you can try yourself and once you did you'll know where to align it in order to mount the lens, without looking at or trying to find the red dot. Useful when it's dark so you can't easily see the red dot.
11-02-2010, 06:29 AM   #7
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If he is referring to pentax A lenses or any pentax K mount lens, and the orange/yellow/white Bump on the lens,. it is alligned to the lens release lever when the lens is in the position to insert the bayonet. This is so you can mount the lenses by feel, in the dark.
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