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08-14-2013, 08:08 PM   #1
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Genuine Pentax M42 adapter - loose?

I have a genuine Pentax M42 adapter and it fits somewhat loosely in my K-30's mount. If the M42 lens doesn't have a tall and wide flange the lens sort of wobbles. Is this normal? Should the M42 adapter sit firm and snug in the body?

08-14-2013, 08:21 PM   #2
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It is normal, it makes it easier to remove from the body, the third party ones fit much tighter and can be very hard to remove. It was designed with Pentax branded M42 lenses in mind, which all have a flange large enough to sit against the mount.
08-14-2013, 08:21 PM   #3
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Wobble is normal for a lens with a narrow base, like the Helios 44-2. The 44M has a wide base and doesn't wobble.
08-14-2013, 08:22 PM   #4
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My genuine adapter seems to fit pretty perfectly on my K-30's and K-01's mount; not much wobble, but not super-tight, either.
One the other hand, I've had two different 3rd party adapters purchased from different places; one I found to fit too tight and the other, too loosely.

08-14-2013, 08:27 PM   #5
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So I have a Mir 1B with hardly any flange and it wobbles and shifts. Assuming the wobble is normal since M42 lenses should have enough flange, what can I do to "tighten up" this mounting combination?
08-14-2013, 09:13 PM   #6
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The adapter is suppose to be a little loose in the mount. The mount face on the lens mates and snugs to the camera mount face. As you have noticed, many FSU (former Soviet) as well as East German lenses have very narrow rears. They fit well on the bodies for which they were originally designed, but not so well adapted to K-mount. Some users on this site have had good luck with a various metal or rubber collars to allow the lens to snug up while still retaining infinity focus.


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08-14-2013, 11:54 PM   #7
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Yes, the way to fix this problem is to make up a ring-shaped shim, which goes between lens and camera body, and bridges the gap between the rear of the lens and the camera. The thickness is critical: too thin and you'll still have a wobble, too thick and you'll lose infinity focus. I've used the stiff plastic covers from boxes of greetings cards, which measured at around 0.23 mm thick. Once you've found the right material, it's pretty straightforward.
08-15-2013, 08:36 AM   #8
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Rather than squeeze a shim-ring-collar between the lens and the body could I instead insert something inside the K-mount mounting surface of the adapter?

08-15-2013, 01:39 PM   #9
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QuoteOriginally posted by 6BQ5 Quote
Rather than squeeze a shim-ring-collar between the lens and the body could I instead insert something inside the K-mount mounting surface of the adapter?
You can try it, but I am fairly confident that it won't work. Your lens wobbles because it (not the adapter) is not fully snugged against the body flange. It might be possible to bend the lugs on the adapter, but I would not try it. You do, after all, want to be able to get the thing off some day, right? (It is designed to be a little loose in the mount for a reason.)


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08-16-2013, 07:46 AM   #10
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The genuine adapter is designed to keep infinity focus on lenses, but it does wobble with narrow-base lenses. Some even say there might be light leaks. So that is its main weakness. But it doesnt require a tool to be removed, it doesnt get stuck, it doesnt prevent the lens from focusing further than a couple meters..
Of course, some Soviet lenses focus past infinity, so you might get away with a flanged adapter. Flanged adapters offer greater stability and generally make sure there are no light leaks. But they can get stuck and have problems with infinity focus. Its a juggling act.
08-16-2013, 08:38 AM   #11
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So how does a regular K-mount lens sit in the body? It doesn't wobble. Are the mounting tolerances tighter there? What presses it up snuggly against the body?
08-16-2013, 12:57 PM   #12
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QuoteOriginally posted by 6BQ5 Quote
So how does a regular K-mount lens sit in the body? It doesn't wobble. Are the mounting tolerances tighter there? What presses it up snuggly against the body?
There are certain makes of the m42 lens that has a based not completely flat (with a small protruded inner circle); with this kind of lens, it will wobble a little once mounted and not very secure. I would use some shims (even a paper cutout) to cushion and level the base when mounting the lens.
08-16-2013, 09:23 PM   #13
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QuoteOriginally posted by 6BQ5 Quote
Are the mounting tolerances tighter there?
No, the tolerances are the same. With a wider flanged M42 lens the lens will snug up properly. To see what I mean, take your adapter and attach it to the lens first (generally easier and the way I prefer to do it) and then put it loose in the mount. Don't twist yet. Notice that it fits and feels about the same as a regular K-mount lens at this point. Now slowly twist the lens to engage the mount lugs a little bit. Notice that the lugs are engaged, but the lens wiggles a little since it is not snugged up. This is also the same as a regular K-mount lens. Slowly twist further while watching the back edge lens flange. Notice that it fits slightly inside the opening of the camera and engages the edge rather than engaging the face. This is not the same as a regular K-mount lens and is why the lens rocks. It has nothing to do with manufacturing tolerances. The adapter's lugs are machined at the same angles and offset as those on a native K-mount lens. The only difference is the dimensions of the lens rear flange.

As noted above, all you need is a very thin shim to fill in some of the space. The suggestion of using a flanged adapter and re-collimating infinity focus might also be a good one. Infinity focus adjustment on many of these lenses is not difficult. One of the users on the Soviet Lens Club thread might be able to assist you with the task.


Steve
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