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07-01-2017, 07:30 AM   #1
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Light leaks with original Pentax M42 adapter ring, on K-1

Is it just my imagination, or really the K-1 is more prone to light leaks, using the original M42 adapter ring?
The problem is already documented, and a few fixes have been suggested (there are a few old post about that): M42 lenses with a tapered back (like the Mir 37mm) don't cover the two cut-out's on the M42 ring, so that stray light gets into the camera.
I often use the M42 adapter rings without the locking spring, unscrewing the tiny screw and trusting the friction provided by the springs inside the camera mount.
This way it's very easy to mount/unmount an adapted lens.
In the past i tried a good number of M42 lenses on Pentax APS-C cameras, with almost no light leaks problems. Most of the times i used unmodified (with screw/spring on) original Pentax M42 adapters.
These days i tried various M42 lenses on my K-1, encouraged by the wonderful results i've gotten with a few of the vintage lenses i've already tested.
To my surprise, i discovered that many of my lenses don't actually cover the cut-out's on the adapter, allowing for plenty of stray light to get to the sensor!
The last examples are a wonderful Steinheil Tele Quinar 4.5/200mm and a Steinheil Cassarit 3.5/100mm.. The back is not tapered, but is too small to cover the front of the adapter ring.
I tried a few different adapters, both Pentax and german made, already tested with full satisfaction.
Both of them were freed from the locking spring... though i don't think it makes any difference.
What is really strange is the severity of the problem, and the fact that i had barely experienced it in the past, with other cameras and of course other lenses.
Is the mount of the K-1 any different from that of the K-01 or K-5 II (my most used cameras before i acquired the K-1)?
Do all old Steinheil M42 lenses show this kind of problem?
The two optics i mentioned have a different build, though. One has the mount threaded on the barrel, while the other has an adjustable mount, not dissimilar from a T2. The build is dissimilar, but both don't cover the cut-out's and leave two rather large slits open to ambient light.
The effect of the light leaks goes way beyond veiling. It is very noticeable in the picture, albeit not so evident in the viewfinder.

I will try to find a remedy using hair bands, or an o-ring of the right diameter/thickness.
The ideal would be a black rubber washer of the right size, but i don't think it would be so easy to find it... If anybody out there found a good solution, please post Ebay/Amazon/whatever link. Thanks.

The reason that made me write this post is different, though.
I'd like to find out if the K-1 is more prone to this kind of problem, and if there are many other M42 lenses that need some kind of "cover" to prevent stray light entering the mirror chamber, and eventually hitting the sensor.

cheers

Paolo


Last edited by cyberjunkie; 07-01-2017 at 07:35 AM.
07-01-2017, 08:03 AM   #2
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This was the main previous thread discussing this Paolo.

Preventing M42 adapter light leaks and dust ingress - an easy solution! - PentaxForums.com

You can see a pic of the 40mm taper washers I acquired locally on p2. I have hunted in vain for a "5 for 99p" similar washers/rings eg on ebay... I think USA market has more prospects.
07-01-2017, 08:53 AM - 1 Like   #3
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QuoteOriginally posted by cyberjunkie Quote
What is really strange is the severity of the problem, and the fact that i had barely experienced it in the past, with other cameras and of course other lenses.
Is the mount of the K-1 any different from that of the K-01 or K-5 II (my most used cameras before i acquired the K-1)?
I'm just guessing here, Paolo, but if there really is a greater tendency for light leaks through the exposed cut-outs on the M42 adapter, maybe it's because the K-1's sensor is bigger than the APS-C models?

Unless I need infinity or long-distance focusing, I now tend to use a flanged adapter. For reasonably close range work, it's absolutely fine and avoids this problem altogether...

Last edited by BigMackCam; 07-01-2017 at 11:08 AM.
07-01-2017, 10:54 AM   #4
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I had already seen the previous posts about the same problem.
I'm using a black hair band now, but i will try to find o-rings of the right size. Flat o-rings should work better, but i'm afraid it would be difficult to find one with the right dimensions.
I prefer flanged adapters, and i've used them for permanent conversions.
Some tele can be adjusted to correctly focus at infinity with the flanged adapter on, but usually some lathe work is needed.
I have no problems doing that on common optics, but a number of my lenses have some collector value, and i would prefer to leave them untouched.
I realized that there is a kind of adapter that would be very useful, but nobody ever made it.
Maybe i will try to make one myself, using a standard non flanged adapter (with no screw/spring), glued to the outer part of a flanged adapter.
The central part of the flanged adapter should be removed, leaving just the space to fully screw the lens to the main adapter. The outer part from the flanged adapter should barely clear the lens, closing the two cut-out's, and allowing to lock the lens in place using the pin of the K mount.
One problem: the resulting adapter would need to be matched to any single lens, cause the diameter of the back of each lens is slightly different from the others. Very likely some foam (or an o-ring) should be used, to be sure to avoid light leaks.
An adapter made this way would leave the register untouched, and still allow to lock the lens in place and cover the opening that give light leaks.
Anybody else had the same idea?

cheers

P

07-01-2017, 10:57 AM - 1 Like   #5
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QuoteOriginally posted by BigMackCam Quote
I'm just guessing here, Paolo, but if there really is a greater tendency for light leaks through the expose cut-outs on the M42 adapter, maybe it's because the K-1's sensor is bigger than the APS-C models?

Unless I need infinity or long-distance focusing, I now tend to use a flanged adapter. For reasonably close range work, it's absolutely fine and avoids this problem altogether...
^^^THIS

The K-1's mirrorbox opening is much larger than that of the APS-C models. On the APS-C models, the M42 adapter cut-out faces a matte-black wall where the mirror box steps down to APS-C size. On the K-1, the M42 adapter cut-out faces the sensor.
07-01-2017, 11:03 AM   #6
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QuoteOriginally posted by photoptimist Quote
^^^THIS

The K-1's mirrorbox opening is much larger than that of the APS-C models. On the APS-C models, the M42 adapter cut-out faces a matte-black wall where the mirror box steps down to APS-C size. On the K-1, the M42 adapter cut-out faces the sensor.
So i wasn't wrong!
I've tried plenty of M42 lenses on previous Pentax DSLR cameras, and i've never found anything so evident

Thanks for the explanation

cheers

P
07-01-2017, 11:15 PM   #7
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QuoteOriginally posted by photoptimist Quote
^^^THIS

The K-1's mirrorbox opening is much larger than that of the APS-C models. On the APS-C models, the M42 adapter cut-out faces a matte-black wall where the mirror box steps down to APS-C size. On the K-1, the M42 adapter cut-out faces the sensor.
QuoteOriginally posted by cyberjunkie Quote
So i wasn't wrong!
I've tried plenty of M42 lenses on previous Pentax DSLR cameras, and i've never found anything so evident

Thanks for the explanation

cheers

P
I have used adapted M42 lenses since the early 1980s with K-mount film SLRs with no problems with light leaks.* Problems occur for lenses whose mount flange is narrower in diameter than the face of the adapter. As noted, reports on this site date back several years and usually involved adapted German (M42), M37 Takumar, and Former Soviet (M42 and M39 Zenit) lenses that were originally intended for use on cameras with similar narrow mount faces. Unless one is using one of those narrow diameter lenses, the potential for light leak through the adapter is almost nonexistent (similar as for native K-mount).**


Steve

* The mirror boxes of K-mount film SLRs extends into the area of the adapter slot creating a vulnerability similar to the K-1.

** Surprisingly, light leaks with K-mount lenses are not as rare as one might think. They happen when a heavy lens is mounted without support (overwhelms the springs that retain the tangs) or when a VERY bright light source is directed at the mount juncture.

Last edited by stevebrot; 07-01-2017 at 11:33 PM.
07-02-2017, 05:04 AM   #8
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I just use the cheap fotodiox ones without the clip, and fill the spaces with epoxy putty (obviously allow to harden before using)

07-02-2017, 06:20 AM   #9
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QuoteOriginally posted by Kozlok Quote
I just use the cheap fotodiox ones without the clip, and fill the spaces with epoxy putty (obviously allow to harden before using)
I'm doing something similar. Living in a 20's vintage frame house with original windows, I have plenty of Mortite kicking around, and when I use my Myer-Optik Gorlitz 4/200, found a little piece over each cutout works great.

Mortite Caulking Cord | Frost KingŪ Products
07-05-2017, 06:47 PM   #10
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I am posting two test pics i've taken, with original Pentax M42 adapter, and leaving the cutouts uncovered.
See how badly the light leaks affect the final image.
The first is taken with a Steinheil Cassarit 3.5/100mm, the second with a Steinheil Tele Quinar 4.5/200mm,
on Pentax K-1




While the Cassarit leaves the cutouts visibly exposed, the Tele Quinar has a T2-esque mount, covering the cutouts almost completely. Nevertheless it gets enough spurious light to ruin the picture
07-06-2017, 09:22 AM   #11
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Mmm quite a dramatic illustration. Did you try some means of covering the mount to see what improvement there was?
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