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Old Nov 17, 2009, 3:38 PM   #1
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Default Manual/Automatic Switch, M42 Lenses Stuck?

Having picked up a Pentax M42 Adapter, I'm getting ready to try it out with my old screw mount lenses. From what I have read, the slide lever on the lens has to be moved from Auto to Manual. The problem I am having is that this lever does not slide or even budge on any of my lenses. Is there something I am missing or is it possible that after being in the Auto position for 30+ years the levers are "frozen"? Any help, suggestions will be greatly appreciated.

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Old Nov 17, 2009, 5:07 PM   #2
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Default I Think I've Found the Problem

There is a very small pin, hardly noticeable that is on the flange next to the threads. When held down, the slider for Manual/Auto operation works smoothly so it can be switched.

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Old Nov 17, 2009, 11:33 PM   #3
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That is because the M42 lenses work differently than the K mount lenses and K mount cameras can not operate the stop down pin.

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Old Nov 18, 2009, 4:09 PM   #4
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Quote:
Originally Posted by bluenose View Post
There is a very small pin, hardly noticeable that is on the flange next to the threads. When held down, the slider for Manual/Auto operation works smoothly so it can be switched.

Regards
This is the proper behavior of a small number of m42 lenses. Only those Pentax lenses made for the Spotmatic F that included the additional linkage that allowed that model and the ES to meter at full aperture have this A/M switch lockout. Those bodies have a groove that let the pin extend and you can't operate the switch when the lens is on the body. If it did operate it could lead to incorrect metering on those bodies.

When these lenses are mounted on older bodies that use stop down metering or have no meters or when mounted on properly made M42>K, or other, adapters the pin is pressed in and the switch will operate.

All of this has absolutely nothing to do with the difference between the M42 mount and coupling and that of the later K-mount.
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Old Nov 18, 2009, 5:15 PM   #5
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Quote:
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This is the proper behavior of a small number of m42 lenses. Only those Pentax lenses made for the Spotmatic F that included the additional linkage that allowed that model and the ES to meter at full aperture have this A/M switch lockout. Those bodies have a groove that let the pin extend and you can't operate the switch when the lens is on the body. If it did operate it could lead to incorrect metering on those bodies.

When these lenses are mounted on older bodies that use stop down metering or have no meters or when mounted on properly made M42>K, or other, adapters the pin is pressed in and the switch will operate.

All of this has absolutely nothing to do with the difference between the M42 mount and coupling and that of the later K-mount.
Thanks for this explanation. The lenses are from my Spotmatic F days so what you have said aids in my understanding. I'm looking forward to trying out the old lenses.

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