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12-21-2006, 03:59 PM   #1
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Stop down method on K-Body (m42 and manual K)

I've read just about every thread I could find here on m42 and older K mount manual lenses, but I still have question regarding fitting it and working with aperture ring in the manual mode on K10D (or alike)

I got couple of lenses for next to nothing (both 135mm 2.8 MCs), one K mount, one m42 mount...

K mount - I think I get the idea: when not in "A" position, blades close and open (and stay there) as I move the aperture ring on the lens, so the true aperture I selected is where the lens blades would stay...

m42 mount - that little pin... Blades do the opposite - close or open depending on the aperture I select on the ring, but only when that pin is depressed. I have not recieved the adapter ring yet, but what puzzles me with m42, how is this pin depressed once the lens is on the camera? Is it done via some drive mechanism in the camera body?

Thanks for puting up with the newbie to Pentax

Regards,
D

12-21-2006, 04:34 PM   #2
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To be able to use the aperture ring on M42 lenses, you have to set the diaphragm to manual using the slider on the lens.

Select the aperture size, and then get the camera to meter the light and set a shutter speed: https://www.pentaxforums.com/forums/pentax-dslr-discussion/1313-metering-smc-m-lens.htm

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12-21-2006, 05:38 PM   #3
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Original Poster
Mo,

Thanks for the reply (though the link does not work) - this is what I found very usefull (not sure if its from the same thread):

QuoteOriginally posted by i.glisin Quote
...

2) Using AE-L button sets correct shutter speed for set aperture: point at the target, hit AE-L and camera will stop down, meter, and adjust Tv. It all takes just a moment! (I use this method 99% of time.) Point at various subjects and keep hitting AE-L to see how it works.
I guess my actual question is to how is the pin on M42 activated within the camera?

More specific, if I wanted to use the M42 lens with the set of non-auto extension tubes on K10D, the tube set (the part that mounts to the M42 lens) would have to have an inner lip that less diameter than the actual thread, where the pin of the lens will push itself against that lip and remain in that position at all times)? Then the adapter M42 to K would be mounted to the other end of the tube to be coupled with the body?

Thanks again!

D
12-21-2006, 06:14 PM   #4
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The pin on a M42 lens has no effect with a K mount body. You must open and close the aperture manually to focus and expose.
In addition, if your lens has the Auto/Manual switch, you should move the switch to manual.

12-23-2006, 01:20 AM   #5
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The pin is just for old Spotmatic cameras. On the K mount Pentax you can use it just in stop-down.
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