Trioplan 2,8/100 N (Exakta mount w/ side button) conversion

[cyberjunkie]

Given the current prices for Trioplan's, i decided to gamble. I have bought a Trioplan N 2,8/100mm in Exakta mount (with the side button), sold as "defekt" on Ebay.de.
It doesn't seem in great conditions, but as far as the diaphragm blades are still there... i guess that what's not working could be fixed, in a way or another.
What appears to be a missing screw at the back leaves me dubious, though

My main problem is that i want to use it on a Pentax full frame, and i don't want to butcher the lens with permanent alterations.
In fact it's everything but a collector's item, Trioplan's were made in great number, but given its current cult status, i'd prefer to cannibalize another optic, if at all possible.
I've seen pictures of the aluminium version in Exakta mount, converted to M42 with a mount very likely taken from another Meyer lens, but those Trioplan's had a (preset) diaphragm ring on top of the lens, while the newer version i found has the diaphragm scale at the other end, and has a very different mount.
It seems to have another ring on top, but what i can see from the pics are just two dots, one white and one red.
I never owned an Exakta camera, but of course the chrome button is there for some reason.
I think it stops down at working aperture one instant before actuating the shutter button on the camera body. Am i right?
Blocking the mechanism to stop-down position should be quite easy, but i would be happy to find a solution that allows to set aside the original mount, and replace it with a M42 one, maybe coming from another cheap/damaged Meyer objective of the same vintage.
Anybody out there tried to do the same?
Any link to a web page that could be of some use?

Here is the lens:








EDIT:
I found this interesting thread on this forum:
http://forum.mflenses.com/exakta-pentax-k-adapter-t9009,highlight,exakta+adapter.html

It 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 (or, even worse, epoxy the LTM ring in place), 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 (0.75mm + 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.

Knowing all that, my question is more specific.
I'd like to know if anybody dismantled the same kind of lens i purchased, and if the "base" of any Meyer lens in M42 mount could be used to replace the Exakta mount of my lens.
From the pictures i've found online i can't tell if it can be done. In most Meyer M42 tele's the mount looks to be retained from the inside, i don't see grub screws or any other way to loosen the mount from the outside.
The only cheap Meyer lenses in M42 mount, with a very similar attachment (via three screws) are the Domiplan and the 1,8/50mm Oreston.
The screws look to be positioned in the same place, and what looks to be an auto-manual switch is more or less where the Exakta mount has the chrome pushbutton.
Thanks in advance for any useful info

cheers

Paolo

[jamaeolus]

Convert your camera to mirrorless?

[cyberjunkie]