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01-03-2014, 12:45 AM   #1
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Using Old M37 Takumar Lenses on newer Pentax Bodies - Light Leak?

So, my M37 to M42 adapter ring arrived yesterday, and now my newly acquired M37 Takumar 58mm f2.4 can be mounted on my Pentax MX. However, I'm rather concerned about the two open slots on the original M42 to Pentax K adapter ring; one having the spring for detaching the adapter and the other on the opposite side.

I've tested with a flashlight with the lens closed, and I found that these slot do allow light to leak into the body.

Will the leak be significant enough to affect my images?

If it does, does anybody here have a nice solution to this problem, other than using tape to cover up these slots?



01-03-2014, 12:47 AM   #2
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I would actually suggest using a non-original m42-k adapter like one of the Chinese types you can find on ebay. The original M42 adapter is designed to accommodate a lens whose barrel is wider than the screw thread, thus causing those leaks to not be a problem. If you are using a M37-in-42 like this, I would actually probably suggest finding a flanged k-mount to m37 adapter ring.
01-03-2014, 02:03 AM   #3
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@kain - But wouldn't that cause me to lose infinity focus?
01-03-2014, 07:27 AM   #4
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You could try a rubber gasket or o-ring outside on the lens to make a seal against the mount, but then you might not see the distance scale on the lens anymore.

01-03-2014, 08:17 AM   #5
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I have never noticed any light leakage (film or sensor) using the Pentax M42 to K mount adapter, and I use it with the relatively small diameter super takumar 28mm f/3.5. Suggest you just go with it and see.
01-03-2014, 07:23 PM   #6
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You are correct about the light leak. I have used M37 lenses on K mount before. I had looked at the idea of machining a slightly recessed flanged adapter for the purpose but the differences between the OD of M37 lenses and the K mount diameter are just too close to allow enough room. The best option I have found which does retain infinity focus is a flange cut from thin rubber. You cut a ring with the inside diameter slightly smaller the the lens od near the mount and larger than the m42 adapter od. By cutting the ID slightly smaller than the lens it deforms the gasket to form a shallow cone. Think of a shrunk down collapsible lens hood in reverse on the wrong end of the lens.This allows the gasket to go over the lens with enough pressure to seal and stay in place. The large end of the cone if cut accuratly will seal against the camera body.
01-03-2014, 07:28 PM   #7
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QuoteOriginally posted by dms Quote
I have never noticed any light leakage (film or sensor) using the Pentax M42 to K mount adapter, and I use it with the relatively small diameter super takumar 28mm f/3.5. Suggest you just go with it and see.
The Pentax M42 adapter was a purpose designed adapter to mount M42 lensed. M42 Takumar lenses have a large enough OD to just cover the edge of the adapter which overcomes the problem of light leaks through the edges of the adapter and the recess for the release catch. M37 lenses have a smaller OD than M42 and do not cover this area.
01-03-2014, 10:48 PM   #8
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If you were just using a DSLR, you could remove the spring from the M42 to K adapter and fill up the slots. I might use plumbing solder or car body filler. The adapter usually has enough friction to hold moderate sized lenses on, as long as the lens controls aren't that stiff. On the MX, one of the slots moves the aperture simulator arm to make the camera's meter think the lens is wide open, so you can't fill up that slot.

01-04-2014, 12:35 AM   #9
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@hagiri_11 you are right, you do lose infinity focus. In my experience with the ones I've used, you still get DoF to infinity if you are at f/5 on a 135mm for f4 on a 50mm.
01-25-2015, 06:56 AM   #10
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I just purchased a Helios 44-2 that is so small in diameter that it barely covers the K mount. I experimented a bit yesterday and sadly, light easily finds it's way through the small openings of my m42 adapter. I have read the suggestions here, but I still wonder what some of you guys do about it. I might try to fill both holes like Just1MoreDave suggested...
I have a picture of the problem and some pictures of the lens as well :

You can see the light leak problem on the sample picture. Flash was fired from right side, about 3m away from the camera. It was a long exposure and there was a house light too on the right side, might have been the cause of the leak...
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01-25-2015, 01:13 PM   #11
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QuoteOriginally posted by kp0c Quote
I might try to fill both holes like Just1MoreDave suggested...
I use one of my daughter's black rubberband hair clips. Doubled up, it is a snug fit around the base of the Helios and completely blocks the light from entering.
01-25-2015, 04:40 PM   #12
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I'll try that - I have a few of those lying around the house as well.
01-25-2015, 04:57 PM   #13
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QuoteOriginally posted by Ikarus Quote
I use one of my daughter's black rubberband hair clips. Doubled up, it is a snug fit around the base of the Helios and completely blocks the light from entering.
Was about to say that -- I've seen those when my wife goes to buy pony-tail hair band things -- they have silicone (or similar) ones that would make a good O-ring. A couple of bucks for a whole pack at any store like Walmart, Target, drugstore.
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