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07-05-2010, 04:17 PM   #1
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M42 converstion to K mount

Is there any way to convert M42 to K without using the M42 to K adapter? I purchased a 400 5.6 M42 for a song in near minty condition, it would be much quicker changing lenses if the mount could be converted or is this just wishful thinking? OOPS I posted in the wrong thread didn't I -

John

07-05-2010, 05:21 PM   #2
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If they can do it with other lenses surely it can be done with an M42. See here there's a bit of a tutorial. Got to be very good with the hands but it doesn't look too hard for someone mechanically inclined and it's got to be easier as they're both Pentax originally.

Converting Topcon lenses to Pentax K
07-05-2010, 06:03 PM   #3
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The easiest way is to remove the tab that locks the adaptor into the lens mount so that you can remove the lens without having to unscrew it. On the Pentax adaptor the tab is held on by a small screw.

If you use a flanged adaptor you can drill the flange in the appropriate spot to engage the K mount's locking pin. If you use an adaptor without a flange (like the Pentax one) then you drill or file the hole for the locking pin in the lens mount.

With a flanged adaptor the conversion is completely reversible but you might lose infinity focus. With a flangeless adaptor you maintain infinity focus but risk lowering resale value through permanently modifying your lens.

I drilled the base of my 3rd party 400mm because its resale value was already negligible and I didn't feel like buying another M42 adaptor. Screwing the lens on and off of the camera was a hassle because of its size and weight.
07-05-2010, 07:20 PM   #4
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Buy a cheap M-42 adaptor then take out the spring on its side.
Just tighten this adapter to the M-42 lens in such a way that it would be hard to unscrew without force, then just leave the adapter with the lens..viola, you have a K-mount lens..no aperture lever though but it would work.
If you have a lot of M-42 lens then the cheap adapters are the way to go.

07-05-2010, 08:39 PM   #5
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A heads up on the cheap adapters. I bought one to test that worked fine ( Actually I initially bought 1 each from 4 different vendors so I could see which was best. 3 of them shipped from the same factory and all were fine.) and then purchased 6 more from one of the vendors - and none of the new ones work.



I had figured the new ones would be made to the same specs as the ones from a month before, but apparently not.

I threw away the screws, tabs and tool first thing, so I don't feel I can rightly ask for a refund.

The new batch seat a little recessed from flush in the camera mount, so if they are screwed all the way onto the lens, they don't reach deep enough into the camera. They'll work fine used the way they are "supposed" to be used, but not permanently attached to the back of a lens.

Not trying to turn anyone of the Chinese adapters, just a reminder to check the fitment of each piece first thing each and every time you order.
07-05-2010, 09:51 PM   #6
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@kxr4trids - Sounds like the solution to your problem is to make some thin shims.

Measure the thickness of the adaptors that work vs. the ones that don't with the precision measuring tool of your choice (Vernier or dial callipers, etc.). Find a sheet of something of the appropriate thickness to make up the difference (aluminum foil, thin brass sheet, overhead transparency plastic, etc). Use one of the adaptors as a guide to cut the shims with a razor blade. Install your newly manufactured shims between the lens body and the out of spec adaptors and your problem should be solved if you are leaving the adaptor on permanently.

If you don't feel like measuring, the same approach will work by trial and error too.

If the adaptors were too thick then I'd suggest using lapping compound, wet-dry sandpaper or a sharpening stone to thin them out.
07-06-2010, 07:48 AM   #7
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QuoteOriginally posted by John Wiggs Quote
Is there any way to convert M42 to K without using the M42 to K adapter? I purchased a 400 5.6 M42 for a song in near minty condition, it would be much quicker changing lenses if the mount could be converted or is this just wishful thinking? OOPS I posted in the wrong thread didn't I -

John
Even if you found a way to graft a k-mount bayonet onto an M42 lens, the aperture linkage is completely different. You would still be left with no automatic stop-down of the aperture or camera-control of the aperture setting, as with a true k-mount lens.

If you found a way to convert the internal aperture mechanism to work like a true k-mount lens, the expense and difficulty would probably make the project unfeasible. Just go buy a k-mount lens and save yourself a lot of time and money.

I think that the only practical way to "convert" an M42 lens to k-mount, is by getting an adapter for each lens, removing the lock tab and leaving it on the lens. I only have one M42 lens that I use on my K10D, a 50mm, f/1.4 Super Takumar. That's what I have done. The adapter stays on the lens.
07-06-2010, 11:06 AM   #8
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QuoteOriginally posted by GerryL Quote
Buy a cheap M-42 adaptor then take out the spring on its side.
Just tighten this adapter to the M-42 lens in such a way that it would be hard to unscrew without force, then just leave the adapter with the lens..viola, you have a K-mount lens..no aperture lever though but it would work.
If you have a lot of M-42 lens then the cheap adapters are the way to go.
Loctite

I too have thought about doing this, and then glueing the threads with loctite to keep the adapter in place.

07-06-2010, 11:28 AM   #9
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M42 converstio to K mount

Wow, thanks for the advice everyone! I have 1 genuine Pentax adapter that goes back and forth between my 28 f/3.5 and the 400 at this point I will probably purchase and modify a cheap one when it arrives and keep it on the 400. It sounds like having surgery done on the 400's mount to permanently convert it would be costly. The M42 400's IQ seems pretty good for it's age as long as I don't open it all the way up, but it's a little on the slow side to fine focus. OH, got to go my hearing service dog needs attention! Thanks again for the advice.
John
07-20-2010, 11:12 AM - 1 Like   #10
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Sorry I'm late here, I'm catching up on old posts

About M42-PK adapters: Three basic sorts exist.

1) Official Pentax adapters are safe and expensive and a bit tedious. I own one.
2) Unofficial clones of (1) are cheap and variable. They MUST have the spring and clip removed OR YOU WILL GO APESHIT! I own a couple dozen.
3) Flanged non-infinity-focus adapter are cheap and safe, but limited in application. I own a half-dozen.

IMHO, the Official Pentax adapter (1) is best if you use and change only M42s all day. Leave the adapter in the camera, screw/unscrew lenses. As I said: tedious.

I put clones (2) on the threadmount glass I intend to use most, intermixed with PK-mount lenses. I use a rear lens cap as a wrench to screw the adapter tightly onto the lens. Once I learned to remove the spring and clip, I've had no problems.

The flanged adapters (3) are best used with some old cheap long teles that focus past infinity anyway; and with bellows and tubes; and for shooting where you don't care about infinity, like portraits and closeups and macros.

Putting any of these adapters on a screwmount lens is as close as you can get, reasonably, to 'converting' the lens. Screw the adapter on tightly, and I almost forget that it's not a PK-mount manual lens. The only lenses that can feasibly, actually be converted, are those with T1 or similar mounts. A lens should only be surgically modified if you have no intention (or hope) of ever selling it.

Another consideration: Catch-In Focus. CIF depends (among other things) on shorting out a certain lens mount contact. PK mounts with shiny bases do so. Shiny flanged adapters (3) do so -- for unshiny ones, file off the paint on the portion of the flange that sits over the contact pin nearest the bottom (6 o'clock) position on the camera mount. Using the (1) or (2) infinity-focus adapters, the screwmount lens may have a wide base to which you can stick a bit of metal tape to short the contact. Narrow-base screwmount lenses won't hold the tape in place, and so either require a flanged adapter (3) or just focus manually, the hard way. I hate doing things the hard way. I'm lazy. And pretty happy.
07-20-2010, 11:50 AM   #11
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Bower

I got the bower adaptor took the metal spring off just keep them on my m42s no problem. I heard the lens will wanna twist but it is not the case so far. I'm getting a few more of these
04-11-2011, 08:54 PM   #12
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I've recently picked up some SMC Tak's (28, 55/1.8, 55/2.0, 200) and I have what appears to be a general brand adapter (says pentax on it, but doesn't look like the one on B&H's site.. I like kxr4trids I find my m42 adapter countersunk into my mounting flange.. I could get a shim made to take up the difference.. and that would work for one of my m42's.. but I have one more thing thats bugging me, Sometimes I want to use Catch In Focus.. SO is there a way to have a flange to cover the 2 AF points and not loose infinity focus on the SMC Taks (since they are narrow based lenses)??
04-11-2011, 09:24 PM   #13
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@chex
No, flange changes registration distance on the camera and therefore you will loose infinity focus.
04-11-2011, 10:19 PM   #14
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well that sucks! I've heard of people using tin foil to bridge the contacts, does that work?
04-12-2011, 02:13 AM   #15
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QuoteOriginally posted by Chex Quote
well that sucks! I've heard of people using tin foil to bridge the contacts, does that work?
Yes. Even better is sticky-back aluminum tape on the lens
.

When you remove the spring clip from the adapter save the little screw. Then when you screw the adapter onto the lens, you can use the screw to lock the adapter in place.

All my m42 lenses have had adapters "permanently" installed. I usually notch the lens base so the locking pin engages; this prevents the lens from falling off the camera and more important, prevents over-rotation of the lens in the mount....if the lens over-rotates you'll have a scary time getting it off the camera.
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