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04-26-2011, 05:13 PM   #1
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ASAHI SMC pentax-M 28MM F2.8 on DLSR?

I have a ASAHI SMC pentax-M 28MM F2.8 lens. When I put attach it to my K-X DSLR a tab on the bayonet moves, opening the lens up all the way. For example I will set the lens to f/22 but once it "clicks" onto my Kx it goes to f/2.8. Even when I move the aperature dial or take a picture the aperture blades dont open or close?
Any way to fix this please,
Thanks Matthew

04-26-2011, 05:30 PM   #2
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You fix it by taking an actual photo, as all k-mount lenses employ open-aperture metering by design. Here are the instructions to follow to ensure that the metering is correct (you pretty much have to stop down manually only for that):

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04-06-2012, 07:55 PM   #3
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I have used the SMC Pentax M 28mm f2.8 lens with my K10D by first setting it to allow me using lenses without A setting in aperture ring with good results fully open with some degree of success, but my sample has "lazy aperture stop-down", so I cannot tell you yet how good it is at other apertures. I hope yours works fine at smaller apertures as well.
04-07-2012, 08:20 AM   #4

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I have such lens. When I put it on my camera I did not worry about the issue which you described. Put the settings on your camera in M mode and go ahead and take pictures. You will not see blades moving while playing with the aperture ring, but when you take picture camera will do that.
Try to take pictures with different aperture but the same exposure time in M mode and you will see your lens works (with higher aperture it will be darker).
Good luck!

04-07-2012, 08:37 AM   #5
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go to M mode, change shutter speed to "bulb"
hold your shutter and you should be able to see the aperture closes.

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