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Getting a Tamron adaptamatic mount lens onto a pentax - mount DIY
Posted By: marcusBMG, 07-10-2018, 09:30 AM

The adaptamatics (1969-1973) were of course pre-PK bayonet introduction so the only adaptamatic mount that works is M42 (+ M42 to PK adapter). The M42 adaptamatic mount is the most common one so it is likely if you acquire one of the lenses it will have that mount, however it may be that you have a lens with one of the other mounts (see heritage cameras info page for a full list). I actually found myself in that position a couple of years ago and converted a miranda mount into a pk mount using a PK reversing adapter to provide the bayonet. This works pretty well, using it just lately I realised that, slightly to my chagrin, it's very slightly off infinity focus.
Adaptamatic mounts alone are scarce, a quick world wide search only pulled up three, all pricy, and no M42. However the M58 locking ring thread of the mount does suggest DIY possibilities, which is the point of this post. I was prompted to look into this by acquiring a nice 300mm f5.6 adaptamatic with a minolta mount.
Unfortunately inspection quickly revealed a fundamental glitch. The locking ring is M58 x 0.5mm pitch; reversing rings/step up-down rings/filter rings are 0.75mm thread pitch. In practice these will engage sufficiently to stay put but only a quarter turn or so. Not very secure! You could try really cranking it on, it look like the lens mount is steel so its the alloy reversing ring threads that will yield. The other aspect is infinity focus. Inspection quickly showed also that any stacking of eg step up/down rings would leave the lens well short of infinity focus. I'm not sure what the actual registration distance is but it's probably not far off the 50mm approx of the adaptall mount. Basically you don't have much leeway to play with.
So the solution is a PK -58mm reversing ring and a ring cut down from a filter with the glass removed. The cut down filter ring is essentially a male to female converter so that the reversing ring will screw on to the lens. There are different designs of filter rings, the type required is one that has a screw retaining ring for the glass. I used a lens spanner to remove that, but simply breaking and removing the glass (care) to free it up is an option.
Pic 1. I used a coarse grit to take off the male thread, finishing with a diamond stone. I used a second filter as a handle and to keep the shape of the ring being ground, and also because the ring gets hot. Then I had to cut a couple of nicks to use my lens spanner to separate them!
Pic 2. The finished ring, the reversing ring and another filter ring, that one was "ready to go" with M58 female thread both sides once the glass (actually plastic) had been removed, but didn't allow infinity focus being thicker, with a rim in the middle.
Pic 3: ring on the reversing adapter.
Pic 4: feels quite firm actually. To make secure the way to go would be a plate from the tripod ring to the bush on the camera body. After this pic I took off a bit more of the ring on the diamond stone to try to get the lens to align at 'O clock instead of quarter to (=of to you yanks).

So this does work, just about hits infinity focus and it's pretty easy to do. Just bear in mind it's not that secure.
If anyone knows a source of M58 x 0.5mm threaded rings let me know. I did inquire at my local engineering works for a similar thing. After a bit of tsk tsk tsk fine threads are difficult they quoted a hundred quid +! So that's out.

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Last edited by marcusBMG; 07-10-2018 at 10:35 AM.
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07-10-2018, 02:22 PM   #2
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I've had a few of the M42 mounts - If I'd realised how scarce they were I'd have sold them for more.
07-10-2018, 03:30 PM   #3
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Is "Adaptamatic" a predeccessor of "AdaptAll"? If so, why would one want to use one since good AdaptAll mounts are readily available for both K-mount and M42-mount??
07-10-2018, 03:58 PM   #4
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QuoteOriginally posted by reh321 Quote
why would one want to use one
No particular reason - just the usual ones of interest, history, their day they were premium lenses, particularly the zooms, exceptionally well made.

Adaptamatic preceded adaptall see

Tamron Adaptall-2 lenses |

07-10-2018, 04:46 PM   #5
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QuoteOriginally posted by marcusBMG Quote
No particular reason - just the usual ones of interest, history, their day they were premium lenses, particularly the zooms, exceptionally well made.
AdaptAll SP lenses, in particular #01A and #23A, are now the primary lenses I use with my Super Program since the ones I used back when it was my primary camera have developed lubrication or fungus issues. But I chose these for their operational, not historical, qualities. That was the reason behind my questions - to see whether these were lenses superior to what I have. If I understand you correctly, interest in these lenses is more historical than practical.

Last edited by reh321; 07-10-2018 at 06:40 PM.

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