Problems w/ M42 to PK Adapters

[Steve M.]

I bought a cheap Chinese adapter to put my Helios lens on a Sears KS1000 SLR. Had to do a lot of filing to get the crudely made adapter to fit into the lens mount recess, and more filing to get the too-thick adapter flush w/ the camera's lens mount. The trouble is that even w/ it flush I still can't quite make infinity using the split prism in the viewfinder as a guide. My shots today confirmed that. If you stop it down to f11 or more it's OK. Anything wider than that and things that lead up to infinity are sharp, but stuff 100 to 200 feet away are not quite sharp. I like the camera a lot so I'll probably just file the lens mount enough to get infinity, or remove the adapter (tricky) and work on that alone, as it seems that the Helios mates only w/ it, not the larger PK mount on the camera.

I know a lot of people here use these adapters, so I'm wondering if others have had this issue. Next time of course I'll get the more expensive Pentax adapter, but as this is my one M42 lens, and since the Sears KS1000 got me away from that Zenit 11 that had exposure issues, this turned out pretty well except for the infinity thing.

 

[nikon_sam]

I bought an original Pentax adapter way back when and used it to mount Vivitar M42 lenses on a Pentax MX body...I just check it with a Takumar 50mm 1.4 lens mounted on a Pentax MX...it focuses to infinity just fine...the only real problem I had with the adapter was getting it to screw on far enough to have the Focus mark at 12:00...I had to sand down part of the back side...

 

[Phil_F_NM]

The true K adapter does not have a flange like the cheap ones do. The cheap ones add about a millimeter of registration to the lens so they will never make infinity focus. The real adapters merely turn the M42 thread into a K bayonet which is wider. The lens registration of M42 and PK is exactly the same which is why it is imperative to use the genuine Pentax adapter. I've never seen a correctly sized one made by another company though I'm not discounting their existence.

Phil Forrest

 

[Steve M.]

Thanks for the feedback. On this adapter, I have the lens lining up well past 12:00 and still don't have infinity yet, but it IS a Russian lens. It seemed to focus fine on the Zenit. By the time I get infinity on the Sears camera I'll be quite a bit further past infinity, but I can live w/ that as long as I have a sharp image.

The odd thing is that since I filed it down (this adapter does not have a flange per se) it's flush w/ the camera's PK mount. Well, this is what you get when you put a Russian lens on a Japanese camera via a Chinese adapter :[ Tolerances are all over the place (though I'm sure the Japanese PK mount registration is on the money).

 

[Phil_F_NM]

It sounds like the lens you have is for a Zenit SLR which had a shorter registration than the standard 46.0mm of the M42. I could be mistaken though, of course.

Phil Forrest

 

[Steve M.]

Ah, so that's the issue. Thanks Phil. If that's the case, then even if I put this lens on an M42 camera (other than another Zenit) I'd still have this issue? Sure sounds like it. I'm not sure that I can file enough off the adapter/lens mount to get correct registration. Might have to unscrew the rear element on the Helios and see if I can change to a different size shim, if there is a shim in there. I did pull the K mount off the camera in the hope of removing shims off the lens mount, but there were none, which is very surprising.

 

[Scrambler]

I'd get a different adapter. I've not heard of a different registration. The PK mount was originally Practika and licensed by Asahi for their Pentax camera.

Cheap adapters are fine but you need one that comes with a removal tool. These have a small spring that locks into place within the PK mount and require the tool to remove. They turn the camera into a screw mount not the lens into a bayonet. They maintain infinity and are a direct copy of the original adapter.

 

[Scrambler]

Wikipedia doesn't exactly agree with me on the East German origins of the PK part but does agree re M42. I might be confusing these two. Bottom line is the same: a proper adapter should sort your problem.

 

[Steve M.]

Yes, my adapter came w/ a removal tool. That's the least of my worries, as the adapter can stay on the camera forever as far as I'm concerned.

I am not sure another adapter is going to help, unless it would sit very recessed into the camera's lens mount. I've looked at photos of the Pentax adapters mounted on cameras, and they fit flush, just like mine does now that I filed it down. But that's not enough. My lens apparently needs to sit closer to the film plane than my camera's lens mount will allow in order to reach infinity. That can't happen unless I file the original lens mount down too, along w/ the adapter as well. The pin on the back of the lens isn't the problem either, as I bent it and jammed it into the lens so I can actuate the aperture. There are no obstructions, the lens screws fully down onto the adapter, which is flush w/ the lens mount. Very strange.

I'm stumped on this one. At this point I'm going to try to shim the rear element of the lens out a little, therefore getting it closer to the film plane and avoiding taking any more metal off the adapter and lens mount on the camera. I'm also hesitant to just buy another M42 mount camera, as it would have the same registration distance, as far as I can see, as the K mount camera that I have w/ a flush fitting adapter. In any event, the lens has to set further in by some means to get to infinity. It's not much that's needed, but it has to happen somehow. There is probably an internal infinity stop on the lens that might be adjusted, but getting to something like that would surely mean disassembling the lens further than I wish to. The rear element should just come out once I remove the retainer, and I can hopefully just shim it from there.

 

[Phil_F_NM]

At this point I'm going to try to shim the rear element of the lens out a little, therefore getting it closer to the film plane and avoiding taking any more metal off the adapter and lens mount on the camera. I'm also hesitant to just buy another M42 mount camera, as it would have the same registration distance, as far as I can see, as the K mount camera that I have.

If you can find someone out there with a Spotmatic, you could test the registration question. You may be able to find one at a yard sale or thrift shop for maybe $10.

As for shimming the rear element, that is going to change the whole characteristic of the lens itself unless you take away the equal amount of shim from the elements forward of the ones you plan on shimming. You need to move the whole optical unit closer to the film plane.

In this case, you may try disassembling the helicoid or at least some of the lens to see if you can adjust where the infinity stop is. Infinity stops are almost never without provision for adjustment. Granted, this is a lens from the FSU but their optical manufacturing was still pretty good, so I'm willing to bet you have some adjustment "past" infinity which can get your whole lens that tiny bit closer to the focal plane that you need.

Phil Forrest

 

[Steve M.]

OK, it's fixed. I simply unscrewed the rear element retainer, as shown in the first photo. The second photo shows the glass element waiting to be removed. Just cup one hand over the lens, turn it upside down, and the glass element and bottom spacer will plop out. Be careful to note the orientation of the glass element so that you don't put it in upside down. Now rummage through your spacer stash (carefully selected from Ace Hardware) and find an appropriate one. Screw things back together and ck things on the camera. I got lucky because my first spacer, a neoprene O ring, was nearly perfect. Since it was neoprene I simply kept snugging it down and let it squash to a point where I had correct infinity focus. The KS1000 is a neat SLR, and it's all ready to go now. Now to film test it.

Why I had to do this, who knows? By the by, shimming the rear element will have no effect on the lens sharpness. I learned this trick when an Elmarit lens that I bought from Igor came to me and would not focus to infinity. Turned out that someone had removed the rear element to clean fungus from it and had forgotten to put the spacer back in. That's also where I learned that Ace is a good store for lens spacers. Lord knows how much Leica would have wanted for it. Thanks to everyone for your help. You learn something every day.

 

[Steve M.]

It worked. I had to redo this post because I originally spent a lot of time grumbling about the Russians, when it turns out the problem was the Italians (me). I accidentally put the rear element in backwards after shimming it, and yes, focus was pretty bad. Now that I have the spacer in there and the element in the right way it is nice and sharp at infinity and at all distances. Senior moments in lens assembly are not good. I also ordered an adapter to try this lens on my Canon T90, which I now think will be a better combo than the Sears KS1000.

Here's what the lens is capable of when the focus is correct. Tri-X in D76. The results would be a lot better if I had something better than a 30 year old flatbed scanner.

 

[Steve M.]

As a further update on this lens, I got my M42 to FD adapter today. I removed the shim that I had installed in the Helios rear element in order to get infinity focus, and put the lens back together exactly as it was in the beginning. Screwed it into the adapter, put it on my Canon T-90 camera, and infinity focus was perfect. So my issue all along was apparently w/ the cheap $6 Chinese M42 to K adapter.