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04-07-2012, 09:12 AM   #1
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M42 Lens with small base

I was wondering if anyone had a solution to this possible issue.

I have several M42 lenses and they all work just fine on my K10 & K20, I usually use a genuine Pentax adapter and have no issue with their operation. Some of the older lenses have very narrow bases (Mir37, Meyer Telemegor, Zeiss 50,etc) and the bases on these lenses are not wide enough to completely cover the Pentax adapter. This leaves the contacts uncovered, as well as the openings for the adapter clips which allows for dust to enter directly into the camera chamber. This usually doesnt concern me too much except on days like today where it's pretty windy out. I have tried using one of the non-infinity adapters (taping over the little slot in the adapter) but of course for other than macro / close-work, and CIF, not the best solution. Has anyone tried to address this before?

04-07-2012, 09:31 AM - 1 Like   #2
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You mean something like this?


Cut out of a soft drink can, very thin and just as you want it?
04-07-2012, 09:36 AM   #3
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That might just do the trick! Thanks!
04-07-2012, 10:25 AM   #4
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Solutions for shortcomings of Pentax engineering.

04-07-2012, 10:42 AM   #5
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QuoteOriginally posted by altopiet Quote
Cut out of a soft drink can, very thin
Do you still keep infinity focus, even with long lenses?
04-07-2012, 11:22 AM   #6
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Infinity??

QuoteOriginally posted by lytrytyr:
. . . Do you still keep infinity focus . . .
Having never actually SEEN infinity, I've wondered just how important it is to be able to focus to it. I'm told I shouldn't expect to find it indoors and hope that if I ever encounter it outdoors the light will be good enough to use less than max aperture so that a hyperfocal distance setting will allow that once-in-a-lifetime capture.


Seriously, the minimal extension (~1mm) involved in using the adapters shouldn't be restrictive when using wide to medium FL lenses outdoors in daylight conditions. I've found the sort of lenses that require thread-to-bayonet adapters are generally used for situations involving less than infinity focus anyway.

It's worth the effort to explore the true effective focus range with those adapters using stop-down viewing of the FoV at practical apertures and during post processing.
04-07-2012, 11:34 AM   #7
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QuoteOriginally posted by pacerr Quote
Having never actually SEEN infinity . . .
I see it on the focus scale of a lot of my lenses.

QuoteOriginally posted by pacerr Quote
Seriously, the minimal extension (~1mm) involved in using the adapters shouldn't be restrictive when using wide to medium FL lenses outdoors in daylight conditions.
That's why my question specifically referred to long lenses.

QuoteOriginally posted by pacerr Quote
I've found the sort of lenses that require thread-to-bayonet adapters are generally used for situations involving less than infinity focus anyway.
I have a narrow-base Meyer 100/2.8 that is sharp wide open.
I would like to try it on my DSLRs, including landscape use at "infinity,"
but share the OP's concerns about uncovered contacts.

Last edited by lytrytyr; 04-07-2012 at 11:44 AM.
04-07-2012, 12:12 PM   #8
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QuoteOriginally posted by lytrytyr Quote
Do you still keep infinity focus, even with long lenses?
The lens you see that on is a Cunor 200mm, and no problem with infinity focus

04-07-2012, 12:22 PM   #9
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Thanks, I'll have to try it with my Meyer.
04-07-2012, 02:29 PM   #10
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QuoteOriginally posted by Laurentiu Cristofor Quote
Solutions for shortcomings of Pentax engineering.
How is that? The lenses in question are not a Pentax product and except for the diameter, thread pitch and general location of the auto-aperture pin there is no real standard for the mount that Pentax "borrowed" from Zeiss/Praktica. That certain DDR and FSU makers opted for a very narrow diameter rear flange on M42 lenses designed for usage on their M42 cameras is a matter of caveat emptor for the K-mount camera owner rather than poor design on the part of Pentax.

The OP mentions exposed adapter clip and dust getting into the camera. That is a new one for me. The only lenses I have seen with that narrow a mount were M39 (Zenit) adapted to M42 and from there adapted to Pentax-K. The usual complaints and fears center on the lens rocking a little and the possibility of moisture getting into the electronics through the contact points. I have often wondered if it might be possible to craft a collar of sorts to slip over the existing rear flange. The collar could then be secured with set screws or cement. To make things even for sweet, a thin rubber gasket could be attached to the collar's face to provide a more effective barrier to moisture and dust.

The best of both worlds...infinity focus and snug lens fit!


Steve
04-07-2012, 02:35 PM   #11
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QuoteOriginally posted by pacerr Quote
Seriously, the minimal extension (~1mm) involved in using the adapters shouldn't be restrictive
That 1mm extension is the difference between 50 yards and the horizon with a 50mm lens. Acceptable, perhaps, but not optimal.


Steve
04-07-2012, 04:46 PM   #12
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I have a zillion lenses, including many narrow-base screwmounts. I don't fret over dust, but I do want the contacts covered so I can use catch-in-focus (CIF) aka trap-focus. I often use a non-infinity-focus wide-flange M42-PK adapter with such lenses. For long lenses (200mm+), the loss of infinity usually doesn't matter, since infinity *is* in focus if I stop down a bit. It's different for shorter lenses; the 1mm thickness of the adapter pulls-in far-focus on a 50mm lens from infinity to maybe 10m. Great for portraits; not so great for 'scapes.

So whether I'm mounting a CZJ Tessar 50/2.8 (12 iris blades, Exakta mount), or Meyer Telemegor 100/2.8 or 180/5.5 (M42), or Jupiter-9 85/2 or J-11 135/4 (M39), the wide-flange adapter lets me use CIF but makes me pay closer attention to subjects -- if they're not with the right range, too bad.
04-07-2012, 05:07 PM   #13
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QuoteOriginally posted by stevebrot Quote
How is that? The lenses in question are not a Pentax product
Exactly stevebrot! However Laurentiu Cristofor never misses an opportunity to dump on Pentax even if it requires fabricating issues it seems.

QuoteOriginally posted by stevebrot Quote
I have often wondered if it might be possible to craft a collar of sorts to slip over the existing rear flange.
I considered doing that but most M42 Taks don't have anything to attach the flange to. Pity because one could incorporate a lens release lock groove as well.
04-07-2012, 06:14 PM   #14
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QuoteOriginally posted by riff Quote
Exactly stevebrot! However Laurentiu Cristofor never misses an opportunity to dump on Pentax even if it requires fabricating issues it seems.
Perhaps, but he usually leaves nice comments on my Flickr stream

It occurred to me a few minutes ago what he may have been referring to. Most other camera makers chose to locate their electrical contacts inside the mount rather than on the mount face when they moved to support more sophisticated features. The same narrow diameter lens adapted to Canon (for example) will not have the issues of exposed contacts and because Canon has a shorter registration distance, the adapter can include a generous wide and very stable flange as well.

All that being said, Nikon and Pentax are the only makers that were able to make the shift to modern exposure control with AF without orphaning legacy glass and that is to the credit for both companies.


Steve
04-07-2012, 09:26 PM   #15
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This is a Mir 37 lens attached to a K10D using an official Pentax adapter. This shows one of the two adapter clip holes that I was referring to in the original post (really narrow flange on a couple of these). The exposed contacts used to bug me a bit but I got over that, and the fact that these smaller flanged lenses do rock a bit doesn't really bug me at all. But this morning when I was shooting the wind would gusting pretty hard at times and while I shielded the camera as best I could during the gusts I would occasionally see specs showing up in the viewfinder (should have been using the 100WR I guess). When I got back in my car I went to put the camera in the bag and the holes on the adapter kind of caught my eye, which was what led to my original question. I only have a few of the smaller flanged M42 lenses that aren't wide enough to cover the entire mount, and I don't shoot with them that often so it's not a huge issue, I was just wondering if anyone else had bothered to deal with this or if it wasn't something to be concerned with.

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Also FWIW I don't see the Pentax design as any kind of engineering shortcoming either. While the majority of my lenses are Pentax brand, I still think that it's amazing that I can use a lens today that I was using on a Spotmatic back in the 70's.

Steve
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