[jrdimond]

I just picked up a 'new' Pentax (Pentax brand) mount adapter K m42 adapter. When I insert it into my K-1 body, it clicks and locks. When I go to unscrew the lens, I hear a faint click and it unlocks from the body. It can be used this way but I am concerned the lens could fall out with just a short turn.

Suggestions?

Thanks!

[Sykil]

My K-1 does the same thing. It's generally not a big deal other than sometimes it dislodges a bit at the extreme end of the focus ring. But I've been shooting a lot with a big, heavy 200 / 3.5 Takumar mounted to it lately and it hasn't been a problem. To get the mount off, I'll either just unscrew it from the lens or put it in another mount that doesn't release when I go to unscrew the lens. I have a *ist DL, K1000, and two K-mount lens adapters for the Q that all securely hold the M42 adapter. I'm not sure why the K-1 doesn't.

[jrdimond]

My K-1 does the same thing. It's generally not a big deal other than sometimes it dislodges a bit at the extreme end of the focus ring. But I've been shooting a lot with a big, heavy 200 / 3.5 Takumar mounted to it lately and it hasn't been a problem. To get the mount off, I'll either just unscrew it from the lens or put it in another mount that doesn't release when I go to unscrew the lens. I have a *ist DL, K1000, and two K-mount lens adapters for the Q that all securely hold the M42 adapter. I'm not sure why the K-1 doesn't.

Oh, nice, I am glad that this is not unheard of. I also am using 2 heavy lenses. One is a ZM-5A 3M-5A F8 8/500 SOVIET TELEPHOTO USSR REFLEX LENS, and the other is the 1000mm version. I am stuck with f/8 but the image quality is amazing. My guess is they were KGB spyware.

Thanks for the fast reply!

[swanlefitte]

With my ks-2 this happens with my 300mm lens but not the 200mm f4 or smaller ones. I have to be more careful carrying it. When shooting i have to cradle the big lens anyway.

[stevebrot]

I just picked up a 'new' Pentax (Pentax brand) mount adapter K m42 adapter. When I insert it into my K-1 body, it clicks and locks. When I go to unscrew the lens, I hear a faint click and it unlocks from the body. It can be used this way but I am concerned the lens could fall out with just a short turn.

Suggestions?

Thanks!

Welcome to the Pentax Forums!

This should not happen with an undamaged genuine adapter, though there is a possible exception when used with SMC/S-M-C Takumar lenses. On the mount face of most lenses in those series there is a small pin that serves as an interlock for the Auto/Manual switch. When it is depressed flush with the face, the A/M switch may be moved freely. When it is not, the A/M switch may be moved from the M to the A position, but once in the A position the switch is locked and should not be forced. Normal action of mounting to camera, attaching to the M42 adapter, or a lens rear cap will depress the pin and normal action to reverse those actions will allow the pin to extend.

The genuine adapter is machined to provide plenty of clearance for extended interlock pin as the adapter is attached and removed. That said, a bent or damaged lock spring may extend beyond the adapter mount face to allow contact with the pin allowing the adapter to rotate free. The contact may be felt as a slight "tick" during the first rotation to unmount the lens at about the 3/4 point and can be visually confirmed with the lens and adapter off camera. The fix is to carefully press the lock spring away from the face such that it no longer contacts the pin.

If you are not using an SMC/S-M-C lens, what lens are you using when this problem happens?


Steve

[jrdimond]

Welcome to the Pentax Forums!

This should not happen with an undamaged genuine adapter, though there is a possible exception when used with SMC/S-M-C Takumar lenses. On the mount face of most lenses in those series there is a small pin that serves as an interlock for the Auto/Manual switch. When it is depressed flush with the face, the A/M switch may be moved freely. When it is not, the A/M switch may be moved from the M to the A position, but once in the A position the switch is locked and should not be forced. Normal action of mounting to camera, attaching to the M42 adapter, or a lens rear cap will depress the pin and normal action to reverse those actions will allow the pin to extend.

The genuine adapter is machined to provide plenty of clearance for extended interlock pin as the adapter is attached and removed. That said, a bent or damaged lock spring may extend beyond the adapter mount face to allow contact with the pin allowing the adapter to rotate free. The contact may be felt as a slight "tick" during the first rotation to unmount the lens at about the 3/4 point and can be visually confirmed with the lens and adapter off camera. The fix is to carefully press the lock spring away from the face such that it no longer contacts the pin.

If you are not using an SMC/S-M-C lens, what lens are you using when this problem happens?


Steve

I just tried it with a Pentax extension tube. The adapter remains locked when I unscrew it, so it does work with the ring, but not the lens. I also have a MC mto-11ca 10/1000 USSR mirror lens, which also exhibits the same problem as the ZM-5A 3M-5A F8 8/500 SOVIET TELEPHOTO USSR REFLEX LENS; the adapter has a faint click and unlocks when I unscrew it.

I also just tried to use my shortest Pentax extension tube with each lens, which would fix the problem if they could focus properly. The issue now is the ZM-5A 3M-5A F8 8/500 SOVIET TELEPHOTO USSR REFLEX LENS does not focus to infinity. I used a cell phone tower maybe 1-2 miles away and it would not focus, but it was close. The 1000mm lens focuser goes way past infinity and I could focus on the tower with room to spare. So, I have a solution for the 1000mm but not the 500mm. This is an issue for me because I do some astrophotography.

Maybe Pentax made a shorter tube? I have a set of 3. The tubes have no size printed on them.Each one has a spring loaded pin that presses on the camera mount.

Thanks for your insight!

[stevebrot]

I also have a MC mto-11ca 10/1000 USSR mirror lens, which also exhibits the same problem as the ZM-5A 3M-5A F8 8/500 SOVIET TELEPHOTO USSR REFLEX LENS; the adapter has a faint click and unlocks when I unscrew it.

Is the lock spring fouling a screw hole on the lens' mount face?


Steve

[jrdimond]

Is the lock spring fouling a screw hole on the lens' mount face?


Steve

The USSR lenses have no pin and unlock the adapter when unscrewed, thus the problem. The extension tubes allow the locking mechanism to hold when being unscrewed and have a spring loaded pin that extends into the camera body when screwed into the adapter. The pin does not touch the adapter. I don't see any function of the pin actually.

I hope I am not missing what your are saying. This is my first try at adapting to a screw in lens.

Thanks for the help!

[swanlefitte]

I checked the pin on my takumar 300 and could not see how it could interfere also. It is past the locking spring when screwed tight. I store my m42 adaptor on my extention tubes so I just tried the lens in the adaptor on the tubes and it remained locked. I might have to pull other cameras out of storage to try.

[jrdimond]

I checked the pin on my takumar 300 and could not see how it could interfere also. It is past the locking spring when screwed tight. I store my m42 adaptor on my extention tubes so I just tried the lens in the adaptor on the tubes and it remained locked. I might have to pull other cameras out of storage to try.

OK, now we have been able to replicate the problem and I have a theory. I think there are to many threads on my USSR lenses, so they go too far into the adapter. The thin metal locking arm meets the threads for maybe 5mm before the lens is tight in the adapter. This shoves the locking arm slightly up, just enough that it barely touches the camera body mounting teeth (I don't know the correct term), not enough to lock the adapter in place. The extension tubes threads don't protrude into the adapter so far, don't touch the threads, therefore they work and the lens doesn't. The lens just goes too far in.

Do you concur?

This of course, does not give me a solution for the lack of infinity focus using the extension tube on the 500mm.

[swanlefitte]

Tried the adapter and 300mm takumar on my k100d and it locks. It is only my ks-2 where it unlocks. I am beginning to think it is the wear on the holding plate of the camera mount. It looks scraped down and rounded on the top corner edge slightly. I tried my 135mm takumar and it does the same if I tighten it very firmly. I think I always tighten the larger lens tighter out of weight bias, making the friction match the lens weight.

[jrdimond]

Tried the adapter and 300mm takumar on my k100d and it locks. It is only my ks-2 where it unlocks. I am beginning to think it is the wear on the holding plate of the camera mount. It looks scraped down and rounded on the top corner edge slightly. I tried my 135mm takumar and it does the same if I tighten it very firmly. I think I always tighten the larger lens tighter out of weight bias, making the friction match the lens weight.

Sounds like we have a similar problem with different reasons. Both ways, it comes down to the ability of the locking arm to firmly meet the camera holding plate.

Thanks for taking the time to troubleshoot!

[stevebrot]

The USSR lenses have no pin and unlock the adapter when
unscrewed, thus the problem.

That I understand. The adapter has a metal catch that engages with the camera's mount that is supposed to hold it in place until you release it. This is usually done with a fingernail. You should be able unmount your adapted lenses leaving the adapter attached to the camera.

In regards to the "pin" I mentioned above, that is a feature of SMC/S-M-C Takumar (Asahi Pentax made) lenses only.

I hope I am not missing what your are saying.

Perhaps a bit. Your adapter may have been modified or damaged at some point. You should be able to insert it into the K-mount opening and rotate it in by hand and it should click into place with the release spring at the 10:00 o'clock position. If this happens without the lens, there is some sort of interaction with the lens that in interfering.

OK, now we have been able to replicate the problem and I have a theory. I think there are to many threads on my USSR lenses, so they go too far into the adapter. The thin metal locking arm meets the threads for maybe 5mm before the lens is tight in the adapter. This shoves the locking arm slightly up, just enough that it barely touches the camera body mounting teeth (I don't know the correct term), not enough to lock the adapter in place. The extension tubes threads don't protrude into the adapter so far, don't touch the threads, therefore they work and the lens doesn't. The lens just goes too far in.

Do you concur?

The lens mount threads should not be in a position to interfere with the small metal spring tab that retains the adapter in the mount, even with a lens having longer thread depth. If the lens threads are shoving the lock spring out of place, your adapter has been damaged and/or might not be genuine Pentax.

As for losing infinity focus with the extension tubes...yes, that is what happens.


Steve

[stevebrot]

It is only my ks-2 where it unlocks. I am beginning to think it is the wear on the holding plate of the camera mount.

I have wondered about that sort of problem. A few of my M42 lenses have very stiff focus rings. As a result, I tend to tighten those pretty tight (when off camera) onto the adapter with the result that the retention catch is subjected to a fair amount of force. So far, I have not had problems, but wear or damage to the catch might be something to be aware of. Potential for damage from a 3rd-party adapter might also be a concern.


Steve

[swanlefitte]

The thin metal locking arm meets the threads for maybe 5mm before the lens is tight in the adapter. This shoves the locking arm slightly up, just enough that it barely touches the camera body mounting teeth (I don't know the correct term), not enough to lock the adapter in place.
Do you concur?

my locking spring is visibly past the outside plane of the threads. That also doesn't explain why mine works on other cameras. My problem could be different of course.

This picture shows the underside of my adapter in the top of my extension tube. In only my ks-2 these parts are sliding over each other meaning one or both need to extend further.