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04-14-2018, 03:45 AM - 4 Likes   #1
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Adapting Altix lenses to Pentax K using an M42 adapter

I recently got hold of a few Trioplan 50mm 2.9 lenses. They all came in Altix mount, for which there are very few adapters out there, and none of them are for Pentax. I saw someone adapting an Altix lens to a Canon EOS camera using an M42 to EOS adapter. They simply filed down parts of the M42 thread until the Trioplan fit into the mount and then glued the lens into the mount. I thought I could do the same with a cheap and cheerful Chinese M42-Pentax knock-off adapter. I first removed the little flange locking the adapter into the camera. I would recommend doing that as they can get jammed in the camera, particularly if the Altix lens locks into the adapter very tightly.

Then I held the lens to the camera to judge where the Altix flanges hit the thread of the adapter and started filing down one section of the adaptert first. I only need to sand down less than 1mm, and I was able to slide and lock the lens into place, without needing any glue at all. Because I didn't find the photos on the original thread very useful, I thought I would put in a few pictures detailling the process.

Here's the lens and the M42 adapter:



Here's the view from the mount:



Here's where I filed down the adapter. It was sufficient to file down on one of the three flanges only:



You slide on the adapter on the thread and push the section you filed down last:



Et voilá - the adapter locks in with a slight wiggle and - unlike the method described on Vintage Lenses, the lens locks fairly tightly and I don't need any glue. It's completely reversible on the lens.



Here is the lens mounted on the K3. Unfortunately I wasn't very diligent which way the lens faced when mounting the adapter, so the aperture scale isn't pointing upwards but sideways. But that doesn't affect the usability.





And finally the bubble bokeh:



04-14-2018, 05:40 AM   #2
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It looks as tho Pentax took a design cue from that knurled focus ring, on their 20-40 Ltd., esp. the silver version.
04-14-2018, 06:52 AM   #3
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What kind of focus distance do you get? Alitix has a register of 42.5mm...
04-14-2018, 08:24 AM   #4
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QuoteOriginally posted by boriscleto Quote
What kind of focus distance do you get? Alitix has a register of 42.5mm...
My question as well. A full conversion to allow infinity focus would require some internal adjustment and/or milling down the lens flange several millimeters.


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04-14-2018, 09:58 AM   #5
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I don't have any direct experience, but from what I've read on other forums, it appears that the Altix lens locking mechanism is actually in front of the flange. Putting an M42 adapter ring hard against the lens body is effectively recessing the lens a few millimeters into the camera body, which may be enough to get infinity focus. On some Altix-mount lenses, there is a risk of the mirror hitting the rear of the lens.
04-14-2018, 03:04 PM   #6
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QuoteOriginally posted by THoog Quote
I don't have any direct experience, but from what I've read on other forums, it appears that the Altix lens locking mechanism is actually in front of the flange. Putting an M42 adapter ring hard against the lens body is effectively recessing the lens a few millimeters into the camera body, which may be enough to get infinity focus. On some Altix-mount lenses, there is a risk of the mirror hitting the rear of the lens.
I found a photo showing the camera with lens removed and you are correct. The Altix had a breech-lock mount with the lens placed forward of a leaf shutter. The lens registration appears to be at the edge of the rim above the silver index pin rather than at the flange by the focus ring. That makes me wonder if a flanged adapter might have worked for this conversion.

Altix-N 1959 - lens removed | East-German 35mm viewfinder ma? | Flickr


Steve

(...am sort of wishing that I had an Altix camera...they look rather elegant...)
04-20-2018, 12:46 PM - 1 Like   #7
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I converted (or I'm going to) all the Altix lenses but the rare Lidyth.
I encourage those interested to go through the hassle to use a M39 to M42 adapter, and only after screw on top of it a Chinese M42 to PK adapter without screw/spring.
Because of the way the PK adapter is made, it is better to fill with glue the inner space between the adapter and the lens, so to be absolutely sure there is no chance of light leaks. I use black hot glue because it would be easy to remove, just in case...
I found that filing a little more than needed allows to turn the inner ring to have the focus/diaphragm reference on top. If it's a little too loose, I use a tiny bit of aluminum foil to make it tight, then I glue.
With the inner ring all the way down, the register is perfect, as by magic With the similar Exakta bayonet some correction is needed.
Filing only one side isn't blasphemy, but of course the lens would be slightly decentered. No effect on performance, as far as the lens is perfectly parallel to the focal plane. I still prefer to file all three sides, though
The Altix mount attracted my attention because of the Trioplan 50mm, but now I think that the most valuable one is the 35mm. The minuscule Tessar 50mm and the tele 90mm aren't bad either. The Tessar is a fine little lens, and all the Meyer's have a beautiful bubbly bokeh.

Last edited by cyberjunkie; 04-20-2018 at 12:53 PM.
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