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05-31-2011, 07:43 AM   #1
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M 400 f/5.6 not stopping down (sometimes)

On Friday afternoon, I noticed that my M 400 f/5.6 was not stopping down, either for exposure or for photos. I took the lens off, turned the aperture ring to the highest number and manipulated the aperture lever to make sure the blades were opening and closing smoothly and quickly. They were zippy, and look completely clean. I put the lens back on and it seemed to be working appropriately. Then it stopped working right again. I pointed the camera straight up, released the shutter, and it was working again.

I took off the lens and examined the aperture lever. It's gotten a lot of use. It actually seems to be worn to the point of roundness on one side. I thought that maybe it's not coming in contact with the camera-side lever that holds and releases the aperture, but if that were the case, wouldn't the viewfinder look dark when the aperture is closed down?

Does anyone know what could cause this, or if it can be addressed without disassembling the lens? (I also cross-posted this in the 300mm+ lens club.)

05-31-2011, 09:07 AM   #2
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Even during normal operation, the lens should only stops down when shooting, or when you have the power ring turned to the stop-down position. Are your photos exposing ok?

If the lever is intact and operational, then it might be a camera problem- I would test the lens on another body if possible.

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05-31-2011, 11:01 AM   #3
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Thanks, Adam. I would be surprised if it turned out to be a camera problem, just because I don't have trouble with any other lenses. This is my reasoning: Far as I know (and my knowledge is limited), all K-mount lenses use the lever to stop down the aperture for shooting, and lenses with an aperture ring stop down for metering as well (when A mode is not engaged or is unavailable). So if this is a problem with the camera, then it should occur across all lenses. I could be wrong.
06-01-2011, 06:16 AM   #4
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I think I may have solved the problem with my M 400/5.6. It looks like the aperture lever was bent slightly inward. I tried to coax it back out, and it seems to be working.

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