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03-31-2017, 03:48 PM   #1
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Has anyone converted a K-mount lens to m42 screw mount?

Maybe hardly anyone would want to put a K-mount lens on one of your m42 Pentax film bodies, but, if you ever did, it is pretty obvious it would be hard and expensive to make a K-mount-lens-to-m42-camera-body adapter.

It would be far easier, I would think, to remove the K-mount flange from a lens and install an m42 mount flange on it.

Has anybody tried this?

How did it work out?

Did the have to settle for the modified lens being only manual aperture (in the sense of how m42 lenses can be auto or manual aperture) ?

Did you need parts from two lenses, or were you able to use parts from some other source?

I'm thinking of converting an old K-mount 28mm to m42, since I don't have an m42 28mm prime lens. It might be a fun project.

03-31-2017, 04:23 PM   #2
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QuoteOriginally posted by goatsNdonkey Quote
remove the K-mount flange from a lens and install an m42 mount flange on it
Obviously the K-mount is bigger than M42 because the adapter screws over it (which is why you can't make a K-mount to M42 adapter). But K-mount and M42 have the same registration distance - which is why you lose infinity focus with a flanged K-mount adapter. So you have really answered your own question: you could remove the mount from one lens and install it on the other (and vice versa). But that presumes the original mounts attach in same way. And, yes, I believe it would be all manual in less you are into some pretty wild engineering.

Last edited by PJ1; 03-31-2017 at 04:26 PM. Reason: add comment
03-31-2017, 04:24 PM   #3
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On all the M42 lenses I own, the rear flange/screw is an intrinsic part of the structure; there is no separating it from the bulk of the lens and reattaching it to something else.

There may be a third-party M42 lens that was constructed that way at some point, but none that I have seen, and certainly not (as far as I can tell) any of the Takumars.

It would be far easier to find yourself a half-decent 28mm M42, and possibly even cheaper, but if you find an appropriate lens and want to try it as an engineering project, best of luck and let us know!
03-31-2017, 04:27 PM   #4
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The screw holes in the mounts will not match up. In fact as PathDoc pointed out, most M42 lenses don't use a mounting plate that's held in place by screws. Drilling and tapping probably wouldn't work either, as the underlying structure may not be substantial enough to support the stress.

I'd just buy a 28mm M42 lens and forget about this type of conversion.

03-31-2017, 04:33 PM   #5
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Since the diameter of the screw mount is smaller then the K-mount even without the bayonet flange the the rear element of the K-mount lens is likely too big to fit in the screw-mount or not enough room to put an adapter with threads. Or you would have to machine down the rear element with threads. Too much effort when it is easier just to pick up a K1000 body.

There is a company that will make custom adapters. I think I priced out a K-mount lens to screwmount body at $190 US. It would be like short 15-25mm (I don't recall the minimum length) extension tube and useless except for macro or closeup work.
03-31-2017, 04:47 PM   #6
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You could use the flanged m-42 adaptor, get you dill handy.Also you will need to re-adjust infinity focus.But why not just buy a Takumar.?
03-31-2017, 04:51 PM   #7
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I'm not surprised that any k lens to m42 body adapter offered might be nearly $200.

I'm not greatly disappointed that robbing an m42 flange from a lens might not be possible, due to those lenses not normally having such a screwed-on flange. I don't have an m42 lens I'd want to cannibalize. However, if someone else has tried it, I would think there were other sources they might go to: m42 extension tube systems, m42 T-adapters, and similar things. If such an object had a separable m42 flange at one end, perhaps it could be adjusted for the right thickness and have mounting holes bored to match the configuration of the mounting holes in the K-mount lens being modified.

I have K-mount film bodies, but what if I want to mount a lens on my Honeywell Pentax ESII (last of the Spotmatic line) that I don't have in m42 mount? I could buy more m42 lenses of course, but if I have a that focal length in K-mount, a copy I hardly ever use, it could be fun to modify it, especially if a simple and inexpensive method were discovered.

---------- Post added 03-31-17 at 06:59 PM ----------

QuoteOriginally posted by niceshot Quote
You could use the flanged m-42 adaptor, get you dill handy.Also you will need to re-adjust infinity focus.But why not just buy a Takumar.?
I only know of flanged m42 adapters the allow use of m42 lens on k-mount bodies. I am talking about going in the opposite direction.
03-31-2017, 05:32 PM   #8
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QuoteOriginally posted by goatsNdonkey Quote
I'm not surprised that any k lens to m42 body adapter offered might be nearly $200.

I'm not greatly disappointed that robbing an m42 flange from a lens might not be possible, due to those lenses not normally having such a screwed-on flange. I don't have an m42 lens I'd want to cannibalize. However, if someone else has tried it, I would think there were other sources they might go to: m42 extension tube systems, m42 T-adapters, and similar things. If such an object had a separable m42 flange at one end, perhaps it could be adjusted for the right thickness and have mounting holes bored to match the configuration of the mounting holes in the K-mount lens being modified.

I have K-mount film bodies, but what if I want to mount a lens on my Honeywell Pentax ESII (last of the Spotmatic line) that I don't have in m42 mount? I could buy more m42 lenses of course, but if I have a that focal length in K-mount, a copy I hardly ever use, it could be fun to modify it, especially if a simple and inexpensive method were discovered.

---------- Post added 03-31-17 at 06:59 PM ----------



I only know of flanged m42 adapters the allow use of m42 lens on k-mount bodies. I am talking about going in the opposite direction.
oh got it. sounds like it wouldn't be worth it.

03-31-2017, 06:32 PM - 1 Like   #9
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we'll just have to convince a manufacturer into creating a full frame, M42 Digital body...

wait... I think I really want one of those...
11-19-2018, 04:18 PM - 1 Like   #10
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This thread may still be relevant to anyone wanting to fit a Pentax K bayonet lens to an M42 screw fit bellows. I wanted to fit a Pentax-A 50mm f1.7 K bayonet lens with a 49mm filter thread to my Pentax II M42 screw fit bellows so that the slide copier would fit the 49mm filter fitted to it. This would then enable me to fit my Pentax K1 MK II full frame DSLR body to the bellows using a conventional commercially available M42 to K bayonet adaptor. I could not find a Kbayonet to M42 adaptor anywhere, simply because no one thought anyone would ever need one. It would extend the lens for a start so would normally only be useful as an extension tube. So, I made my own...and quite a simple project it turned out to be. I simply cut the end off a Pentax K lens cap. Fitted an M42 T2 adaptor to it. Fitted a small screw to lock the lens in place, fitted the lens and the assy to my bellows, fitted the K/M42 adaptor to my camera and fitted that to the other end of the bellows, together with the slide copier in place and hey presto! Only image I have of the set up at present. More details can be made available to those interested.
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11-20-2018, 03:34 AM   #11
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QuoteOriginally posted by emergo Quote
we'll just have to convince a manufacturer into creating a full frame, M42 Digital body...

wait... I think I really want one of those...
I'm surprised no one has tried tbqh.
11-20-2018, 07:19 AM   #12
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QuoteOriginally posted by ZombieArmy Quote
I'm surprised no one has tried tbqh.
no one has built one and the topic has been discussed at great length by people here on the forum.

pentax has gone as far as any reasonable company in terms of backwards compatibility by offering M42 to K adapters and by carrying forward legacy (film) lens support on all bodies when neither nikon, or cannon have done so, In fact over time cannon has abandoned their legacy lens series twice.

why would a company struggling, as pentax does for market share on K mount DSLRs make it even worse by developing a very niche market body? the demand just is not there.
11-20-2018, 09:24 PM   #13
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QuoteOriginally posted by Robin58 Quote
This thread may still be relevant to anyone wanting to fit a Pentax K bayonet lens to an M42 screw fit bellows. I wanted to fit a Pentax-A 50mm f1.7 K bayonet lens with a 49mm filter thread to my Pentax II M42 screw fit bellows so that the slide copier would fit the 49mm filter fitted to it. This would then enable me to fit my Pentax K1 MK II full frame DSLR body to the bellows using a conventional commercially available M42 to K bayonet adaptor. I could not find a Kbayonet to M42 adaptor anywhere, simply because no one thought anyone would ever need one. It would extend the lens for a start so would normally only be useful as an extension tube. So, I made my own...and quite a simple project it turned out to be. I simply cut the end off a Pentax K lens cap. Fitted an M42 T2 adaptor to it. Fitted a small screw to lock the lens in place, fitted the lens and the assy to my bellows, fitted the K/M42 adaptor to my camera and fitted that to the other end of the bellows, together with the slide copier in place and hey presto! Only image I have of the set up at present. More details can be made available to those interested.

Just link to your own thread on the subject:
K1 II and home made M42/K adaptor for fitting M42 screw fitting items. - PentaxForums.com
08-10-2020, 10:45 PM - 1 Like   #14
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QuoteOriginally posted by Robin58 Quote
This thread may still be relevant to anyone wanting to fit a Pentax K bayonet lens to an M42 screw fit bellows. I wanted to fit a Pentax-A 50mm f1.7 K bayonet lens with a 49mm filter thread to my Pentax II M42 screw fit bellows so that the slide copier would fit the 49mm filter fitted to it. This would then enable me to fit my Pentax K1 MK II full frame DSLR body to the bellows using a conventional commercially available M42 to K bayonet adaptor. I could not find a Kbayonet to M42 adaptor anywhere, simply because no one thought anyone would ever need one. It would extend the lens for a start so would normally only be useful as an extension tube. So, I made my own...and quite a simple project it turned out to be. I simply cut the end off a Pentax K lens cap. Fitted an M42 T2 adaptor to it. Fitted a small screw to lock the lens in place, fitted the lens and the assy to my bellows, fitted the K/M42 adaptor to my camera and fitted that to the other end of the bellows, together with the slide copier in place and hey presto! Only image I have of the set up at present. More details can be made available to those interested.
Great work! Only useful reply in the thread. Thanks!
08-11-2020, 01:51 AM   #15
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This is what I like about Pentax Forums - a great resource that can help someone in the future. Compare that to the trash called FB where everything drops down to obscurity.
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