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11-21-2016, 11:41 PM   #1
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PK/M42 conversion: Meyer Trioplan 2,8/100mm in Exakta mount

I want to try first this Pentax-specific forum, cause it's the one I like the most, and cause I've always liked the threads about lens adaptation (and tinkering in general ).
I suppose others share my preferences... so I'm asking for help/infos on at first, not on other more specific fora.

I already adapted a small Trioplan in Altix mount to M42, and I'm in the process of doing the same to a 3,5/75mm Trioplan on leaf shutter, using a recessed flange and a cheap Chinese focusing helicoid.
Now I have a have a more valuable lens, and I don't want to do anything I would actually regret. Hopefully I'd like to adapt the lens in a reversible way, that would not affect the value of the lens as collectible.
Before tackling this project, I'd like to get as much infos as possible, proceed with some caution, and find if another dirty cheap Meyer lens could be cannibalised, swapping the mount between the two objectives.

The lens that has to undergo surgery is a Meyer Trioplan 2,8/100mm, black version, with Exakta mount (WITH the side chrome pushbutton that activates the shutter release on the camera body).
Pictures of this variant of Trioplan are very easy to find, so I'm not posting any.
I will, if I'm required to.

I bought this lens for relatively cheap, because the barrel is somewhat worn, and the lens was sold as "defective".
From what I see from the images, it's a risk worth taking... but the lens is in no way pristine, so as a last resort I could even accept the idea to permanently modify it.

Any first hand experience, link to Web pages , etc, etc is welcomed


11-22-2016, 03:18 AM   #2
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I suggest you read the thread of methusalem. The author can be contacted, he normally quickly responds.

Das Trioplan...Es gab 50mm ? Pentaxians
11-23-2016, 01:01 AM   #3
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Original Poster
Just checked, he has the M42 version. No need for any adaptation, just a M42 to PK ring!
BTW, cheap chinese adapter rings often need to be filed (with a sharpening stone or small file), and invariably you'll get the diaphragm/focus indicator all over the place... but on top
Original Pentax adapters, or german made ones (like Hama's) are perfectly fine.

I'd like to find out if any forum user attempted the conversion of a Meyer lens in Exakta mount (with side button) to PK/M42 mount.
From the pictures i have the impression that different lenses shared the same components.


11-23-2016, 01:52 AM   #4
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I would have asked him. You know this thread I assume?

or here:,highlight,exakta+adapter.html

11-23-2016, 06:56 AM   #5
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QuoteOriginally posted by UlrichSchiegg Quote
The link you gave me reports the same approach i would try if no other, cleaner way is feasible.
Unfortunately to solidly fit the adapter i'd need to drill three or four small holes on the lens mount, remove the button, and find a way to fix the diaphragm in stop-down position (i have seen no manual-auto switch on my Trioplan). All that taking for granted that the focusing helicoid has enough room for adjustment to compensate for the difference in register + the thickness of the M42 to PK flange (1mm minimum).
I have already converted a few lenses in Altix mount to M42, including the Trioplan 2,9/50mm.
The process is similar to the Exakta mount conversion, it just doesn't need to compensate for the difference in register, cause the LTM ring (mounted flush with the back of the lens) gives exactly the register required by PK and M42 mounts.

My request was more specific. I'd like to know if anybody dismantled the same kind of lens i purchased, and if the M42 mount of a Domiplan 50mm or a Primoplan 135mm could be used in place of the Exakta mount of my lens. From the pictures i've found online i can't tell if it can be done. The M42 mounts look to be retained from the inside, i don't see grub screws or any other way to loosen the mount from the back.

What i wrote is true is only partially true.
It seems that all Meyer tele's have the mount/base part retained from the inside, while the Domiplan and the Oreston 1,8/50mm, in both Exakta and M42 mounts, are attached via three screws that look to be exactly in the same place as in my Trioplan.
Even what looks to be an auto-manual switch is positioned where the Exakta's chrome button is attached...
There could be some hope
Before actually buying one, it would be nice to get a confirmation from someone who opened a black 100mm Trioplan (for example to clean diaphragm blades or dirty glasses)



Last edited by cyberjunkie; 11-24-2016 at 12:54 AM.
04-06-2017, 06:12 AM   #6
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Hi, I was wondering if you finally found a solution.
I am having some problem in an adaptation attempt not so different the one you are trying to do.
I'm sending you a PM to explain it all (I wrote in Italian, hope that's OK for you).
Sorry to all else for my weak help at the moment, I promise I'll publish any useful update later.

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