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02-11-2018, 09:34 PM - 4 Likes   #1
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PK-ization of the Industar-50

This post is about the adaptation of the Industar-50 on a PK body. The classic alternatives are well known and discussed for instance here:
Converting M42 mount to K-mount - PentaxForums.com
but I can't find online the way I have done it.

the Industar-50 in M39 can be mounted:

- with a M39-PK adapter, I know only one kind, flanged:





it has the notch for the pin lock, so easy to put in and out, and it covers the pk bayonet external connectors on the camera body:





but the flange puts the lens ahead and infinity focus is lost



- with a M42 recessed adapter on a M39-M42 ring. Which is also the way to mount the M42 version of the Industar-50:

the M42-PK Pentax or replica:




inconvenient: the lens must be unscrewed and the wrench used to extract the M42-PK adapter every time.
And the connectors ring of the body is not covered:








So I wanted to cut the M39-PK adapter, to keep just the external lip with the locking notch, and set it around the base edge of the Industar-50, in order to get a locking, infinity compatible, and large enough to cover body connectors, mount.

the base of the Industar-50 is 50mm.
The idea was to use:

- hole cutting saw blade of 51mm, in order to leave ~1mm between the hole cut in the M30-PK adapter and the lens base
- epoxy putty, to fill in the gap around the lens base and the cut ring.
- sand, brush/polish and paint black
- set the M39-M42-PK adapters together on the lens with blue threadlocker (removable)

the retainer clip on the M42-PK adapter is of course removed (otherwise impossible to unmount the lens)


Industar-50 are very cheap so no need to be afraid.


I have done this relatively fast, without perfect sanding job. It's good, but not pretty.


the M39-PK adapter to be cut, and the hole saw blade:






the M39-PK must be immobilized somewhere somehow. I just screw it on a piece of plank clamped to a table:





it wasn't secured enough with just screws holding it by the edges and it started rotating with the hole saw, I had to bore three small holes in order to immobilize well the M39-PK. A bit messy but working solution:





ok, so M39-PK adapter lips cut off:




some fine sanding of the edges:






now, protect the lens with blue painter masquerading tape (put some piece of paper pulp like toilet paper between the tape and the glas front and back).
Only the base edge of the lens is uncovered, that's were the epoxy putty will "weld" the M39-PK ring:




cut a bit of epoxy stick, mix and knead it, position the ring around the lens base and fill the gap with the epoxy putty. From now on I will pay attention to keep the red point and the locking notch.








then sanding, brushing, polishing. I applied putty twice in order to have a full filling, and sanding before the second coat. This can be done much better, I just did it good enough, not until pretty. On the first picture (back of the lens) the dried epoxy putty is seen in grey, between the base of the lens and the mounting ring:






carefully wax any dust, and clean with denatured alcohol, remote the masquerading tape, fix edges of the epoxy area, clean again:





Masquerading tape again, and ready for paint job. I used a spray of regular metal primer and a spray of black paint. Next time I will use a flat black, the one here is glossy.


So, result of the paint job:





i was careful to masquerade the red point and the notch, on the back:





Next, blue threadlock on the M39-M42-PK adapters, and blue threadlock on the lens thread:




here we can see there ~1,5mm thickness difference between the M39-M42 brass ring and the M42-PK adapter (so will it affect infinity focus?):







End result:









Mounted on a camera:







also, I have metal hood for this lens, it clicks on the aperture ring, so the hood is in fact convenient for setting aperture (It's possible to very carefully epoxy glue the hood on the lens)




02-12-2018, 01:11 AM   #2
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That's a lot of work! Very well done!
02-12-2018, 09:18 AM   #3
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So, if I understand correctly, you're converting a Soviet M39 lens to have the proper K-mount locking, with infinity focus?
02-12-2018, 10:24 AM   #4
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QuoteOriginally posted by timw4mail Quote
So, if I understand correctly, you're converting a Soviet M39 lens to have the proper K-mount locking, with infinity focus?
exactly.
The M39-PK adapter locks on the pin of the body, but the thickness of the flange breaks infinity focus. The recessed M42-PK adapter (screwed around a M39-M42 ring) keeps infinity focus but must be removed with the wrench after unscrewing the lense every time and screwed again on the lens for the next use. Very inconvient. So I made an hybrid. Thanks to the peculiar form of the Industar-50 it's easy to set a locking flange around the base. Epoxy putty work well for this.

I searched for a while, included on runet, but didn't found this kind of solution. Am interested about former experiences, variants, etc.

I worked fast, so it's not pretty, epoxy job and sanding could had been better and more accurately done, but the back of the flange is alright enough and functionality good. The paint also was not the finest for this kind of job.
See the esthetic flaws:







and it's good to have now a "regular" K mount with it's rear cap:



02-12-2018, 10:38 AM   #5
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QuoteOriginally posted by landstrykere Quote
exactly.
The M39-PK adapter locks on the pin of the body, but the thickness of the flange breaks infinity focus. The recessed M42-PK adapter (screwed around a M39-M42 ring) keeps infinity focus but must be removed with the wrench after unscrewing the lense every time and screwed again on the lens for the next use. Very inconvient.
Just for clarity - and for the benefit of other readers - if an M39 SLR lens focuses to infinity using an M39-M42 step-up ring and M42 adapter, it must already have been modified for the M42 flange focal distance of 45.46mm, as M39 SLR ffd is 45.2mm. That's potentially a fairly easy modification for lenses like the Industar-50... it could be as simple as removing the optical block pin that limits the focusing between MFD and infinity, rotating the optical block until infinity focus is achieved, then positing the focusing barrel to read correctly. It might also require removal of some material from the base of the focusing barrel...
02-12-2018, 11:22 AM   #6
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QuoteOriginally posted by BigMackCam Quote
Just for clarity - and for the benefit of other readers - if an M39 SLR lens focuses to infinity using an M39-M42 step-up ring and M42 adapter, it must already have been modified for the M42 flange focal distance of 45.46mm, as M39 SLR ffd is 45.2mm. That's potentially a fairly easy modification for lenses like the Industar-50... it could be as simple as removing the optical block pin that limits the focusing between MFD and infinity, rotating the optical block until infinity focus is achieved, then positing the focusing barrel to read correctly. It might also require removal of some material from the base of the focusing barrel...
I'm pretty sure my Tair-11 has that modification.
02-12-2018, 10:00 PM   #7
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QuoteOriginally posted by BigMackCam Quote
Just for clarity - and for the benefit of other readers - if an M39 SLR lens focuses to infinity using an M39-M42 step-up ring and M42 adapter, it must already have been modified for the M42 flange focal distance of 45.46mm, as M39 SLR ffd is 45.2mm. That's potentially a fairly easy modification for lenses like the Industar-50... it could be as simple as removing the optical block pin that limits the focusing between MFD and infinity, rotating the optical block until infinity focus is achieved, then positing the focusing barrel to read correctly. It might also require removal of some material from the base of the focusing barrel...
some users have infinity focus problems with the M39-M42-PK setting, some not.... many Industar-50 have been tweaked in a diversity of ways, and it may be hard to know the history of the lens. Untouched ones will come directly from old soviet stock.
For people around the Baltic (my case) when in week-end in Saint-Petersburg, there's a small shop in Gostiny Dvor where an Industar-50 costs ~10eur,
Anyway the fun with it, is that it's easy to disassemble and play with:




this guys shows a servicing, and focus tweaking in order to use the lens with a M42-EOS adapter:


this one, just moves the rear element for use with a Nikon:

Modifying Russian lens for Nikon (Industar 50-2) by FX-1988 on DeviantArt

etc.
03-17-2018, 07:20 PM   #8
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Good job! I have a M42 version of this lens, use it with K-01. At f/5.6 it is surprisingly sharp, the center is probably sharper than my DA 40 limited.

03-18-2018, 04:21 AM   #9
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QuoteOriginally posted by BigMackCam Quote
Just for clarity - and for the benefit of other readers - if an M39 SLR lens focuses to infinity using an M39-M42 step-up ring and M42 adapter, it must already have been modified for the M42 flange focal distance of 45.46mm, as M39 SLR ffd is 45.2mm. That's potentially a fairly easy modification for lenses like the Industar-50... it could be as simple as removing the optical block pin that limits the focusing between MFD and infinity, rotating the optical block until infinity focus is achieved, then positing the focusing barrel to read correctly. It might also require removal of some material from the base of the focusing barrel...
And for maybe more clarity, this is the Industar M39 SLR lens, not the Industar Leica screwmount lens, which has a very different flange distance and would not be helped by something like this...

So this would not work on the 50mm lens off a Fed rangefinder, for example...

-Eric
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