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01-06-2012, 07:58 AM   #1
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using pentax m lenses like m42

Hi,

I have both 50mm Pentax M f/1.7 and M f/1.4, and though i find the image quality excellent i really don't like to use the green button system on my k-7 or just being able to use Av mode when they are at their maximum aperture. In this way, i find the old m42 much more practical, especially when using them with the A mode, where the aperture ring is conected directly with the diafragm blades (allowing the full use of the Av mode).

So, my question is: is it possible to convert old pentax m lenses to work as the m42, for example by removing the diafragm clutch, or stoping them permanetly to the correspondent of the aperture ring?

Thanks.

01-06-2012, 08:03 AM   #2
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If you could make the diaphragm manual (i.e. by removing the aperture lever that goes into the camera), then yes.

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01-06-2012, 08:09 AM   #3
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Did anyone remove the aperture lever before? is it complicated?
01-06-2012, 09:31 AM   #4
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It depends on the individual lens. On a few, the lever itself comes off. On many M lenses, the lever is an integral part of the whole mechanism that ultimately moves the blades. If that mechanism is removed, the blades aren't attached to the aperture ring any more.

You can put the lenses on the camera without rotating them fully. Stop about 10 degrees short, and the camera's actuation arm won't move the aperture lever at all. Then the aperture ring is the only way to control the blades. The lens is fairly secure unless it's really heavy or has a stiff focus ring. If you like this, drill a second hole for the lens locking pin and the lens will be locked in securely.

01-06-2012, 09:35 AM   #5
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why not just use an m42 50mm 1.4 / 55mm 1.8 then? it would seem to me that the annoyance of having to unscrew the lens and remove the adapter to use Kmount lenses is a lot less work than trying to hack apart a perfectly functional lens.
01-06-2012, 09:35 AM   #6
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If you don't mind butchering a lens and killing its resale value, you could cut or clip off the lever. But yes, just get M42 lenses. It's not like they're rare.

Last edited by RioRico; 01-06-2012 at 10:05 AM.
01-07-2012, 05:48 AM   #7
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Someone posted that if you drill a second locking pin hole about 3/8 of an inch away from the first, and partially mount the lens you can do it.

Still I am not sure I would do this,

As rio says just get some M42 lenses. If you want similar coatings get SMC taks
01-07-2012, 11:58 AM   #8
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Drilling a second locking hole is pretty fast and nearly non-destructive: if you want to use your lens as intended for a M lens (or on a film body), you just have to use the original locking hole.

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