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03-24-2011, 08:51 PM   #1
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K mount adapter for M42 bodies?

I know there exist both Pentax and third-party adapters that allow the old Takumar lenses to be mounted on post-1975 bodies.

Is there an adapter that goes the other way, so that K, M and A series lenses can be slotted onto Spotmatic-like cameras?

And if there is, are there focussing problems inherent at closeup and infinity? I guess the metering would automatically be stop-down, since there's no fully-open setting on the SMCP lenses.

03-24-2011, 08:53 PM   #2
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Nope...the registration distance is the same, but the K-mount has a larger diameter...


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03-24-2011, 08:53 PM   #3
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Nope, the k-mount is physically bigger than the M42 mount, so there is no way to make an adapter..


EDIT: Ya beat me to it !! haha
03-24-2011, 09:02 PM   #4
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Thanks. Technically an adapter is still possible, mechanically speaking, but I guess the quarter-inch or more protrusion so that the K-lens is fully outside the body would screw the framing (thus affecting focusing and image quality) up so seriously it wouldn't be worth doing.


Last edited by asaru; 03-25-2011 at 07:47 AM.
03-25-2011, 07:37 AM   #5
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QuoteOriginally posted by asaru Quote
Thanks. Technically an adapter is still possible, mechanically speaking, but I guess the quarter-inch or more protrusion so that the K-lens is fully outside the body would screw the framing (thus effecting focusing and image quality) up so seriously it wouldn't be worth doing.
No infinity focus without an auxiliary lens...not worth it! This is particularly true considering the amount of very high quality glass available in M42 including relatively modern Tamron Adaptall-2 and recent Zeiss models.


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03-25-2011, 11:54 AM   #6
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The other option: mod the camera. Replace the M42 mount with a PK mount. I've seen folks reporting that they've removed native mounts from old Canikon SLRs, replaced with PK. Of course, PK SLR's aren't really rare nor costly, so... why bother?
03-27-2011, 04:12 PM   #7
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Why bother? If you want a Spotmatic-like experience with a K-mount camera why not get one of the early Pentax K cameras, a K1000 or a MX?
03-27-2011, 05:47 PM   #8
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To Tom and Rio: I have a small stash of bayonet-mount lenses I've collected over the years to mount on my two MX bodies, but a little while ago I got bitten by ancient-camera fever and obtained a functioning SL with a single normal Takumar lens. Thus the obvious question and the exhaustive answer. I'm not much of a mech-modder, though.

Shooting the SL, by the way, is totally unlike the MX. The unmetered-manual mode makes all the difference!

03-27-2011, 06:04 PM   #9
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You could look for a 1.4x teleconverter and take the rear mount off and attach a screw mount from a diner lens
03-27-2011, 06:08 PM   #10
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QuoteOriginally posted by Tom in Delaware Quote
Why bother? If you want a Spotmatic-like experience with a K-mount camera why not get one of the early Pentax K cameras, a K1000 or a MX?
Or even better, a KM...KM


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03-27-2011, 06:14 PM   #11
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Steve: a KM is the matchneedle k-mount spottie with DOF preview, right? I think the over-under MX LEDs are basically the same -- the difference comes when the meter's taken away and the light has to be eyeballed (quite the rush....)

Lowell: Thanks for the idea. Do you suppose modifying a single short extension tube in the same way be optically better, perhaps?
03-27-2011, 06:15 PM   #12
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No modifying an extension tube will cost you infinity focus. The elements In the TC will correct for this
03-27-2011, 06:20 PM   #13
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Aha. But a 1.4 TC basically makes standard optics into DSLR optics... I suppose something really baroque would be stacking a modified 1.4x TC and a front-end 0.7x wide-angle adapter. I think, though, based on my experience with teleconverters, that would be a good two or more stops lost, never mind the aberrations introduced...
03-27-2011, 06:44 PM   #14
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The TC will cost a stop not 2. I would avoid the front end adaptor

The other option is to as others have suggested just get a body with a k mount

If you want the feel of no metering just take the batteries out. The shutter will still work because it is mechanically timed
03-27-2011, 07:55 PM   #15
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OK. Thanks. So just to recap.



1. I have shot metered manual, with an MX, since the mid-eighties.

2. Intentionally crippling the MX by pulling the batteries out is artificial and for me, anyway, doesn't really work.

3. I have an unmetered SL. Shooting with it does work.

4. I'm not in the market for more cameras.

5. My question has been, can the MX lenses be mounted on the SL.

6. There seems to be no really good solution.

7. The one possible way without losing focusing range nor changing the effective focal lengths, and that is with a modified one-stop losing teleconverter at the back and a one-stop (presumably) losing wide-angle front-end, is not good optically nor recommended.

8. I guess I'll just need to explore the limits of 55mm:1.8 for when I want to shoot unmetered. And save up for more good M42 lenses, perhaps.

Thanks, guys.

Last edited by asaru; 03-27-2011 at 08:02 PM.
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