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03-19-2014, 12:42 PM   #1
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Mir 1B 37mm lens, adapters, mirror bumping

My cousin gave me an exceptionally clean Mir 1B lens last summer and it's been somewhat difficult for me to use it on my Pentax bodies.

First issue comes from the body mating surface. It is very small. The OEM Pentax K-M42 adapter is meant to fit loosely in the camera and the lens should screw on snugly against the camera mating surface. Since the Mir 1B lens has such a small mounting surface it can only mount itself to the adapter, which is loose and thus the whole lens assemble wobbles. I overcame this problem but getting a cheap Chinese made K-M42 mount adapter that is readily available on eBay. The specific one I am referring to comes with a removal tool. It fits well enough in the camera and it's actually easy to take out. All it needs is some gentle massaging and it's out in 15 seconds. The nice thing about this adapter is that it fits snugly enough to not wobble. When I screw on the Mir 1B lens it is solidly mounted.

Second issue comes from an inability to achieve infinity focus. I feel like I need just a tiny bit more of rotation and I'd be there. Stopping down to f/8 helps since that increases my DoF but it's not perfect. The Chinese adapter is noticeably thicker, if even by a few mils, than the standard OEM unit. Lay them on a table side by side and the difference is easily seen. I overcame this issue by sanding down the surface of the Chinese adapter. It's made of brass and it slims down fast on a belt sander.

So now I can solidly mount the lens and achieve infinity focus. The third issue comes into play when I try taking a picture. It seems like the rear of the lens blocks the mirror from rising! I'm not hitting the rear lens element. There's enough protective material around the lens.

I'm kind of bummed out here because I really want to try this lens and I can't seem to get it to fit. Does anyone have any suggestions on how to get this lens working properly?

(Note: the idea of getting a K-01 did pass through my mind but ... but ... but ... no, I can't.)

03-19-2014, 03:02 PM   #2
dms
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Maybe you can file down the rear of the lens housing (where the mirror hits) so the mirror clears it. Seems like your already in "for a pound."
03-19-2014, 04:12 PM   #3
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QuoteOriginally posted by 6BQ5 Quote

First issue comes from the body mating surface. It is very small.
Second issue comes from an inability to achieve infinity focus.

The third issue comes into play when I try taking a picture.
This is my Mir 1 - an early version, M39 (with adapter to M42)
Issue 1: yeah this is a nuisance. Aditionally, my K-r has exposure compensation issues when using AV mode. One way of trying to get around those is to make a contact with aluminium foil (on the normal non conducting black mounts). Since this mount doesn't cover the contacts, there is no possibility of a connection nor of using tricks like foil.

My lens doesn't have infinity focus problem - or rather if it has it focuses past infinity. See my Mir relubing guide for another comment and perhaps a bit of insight on this...

I am a bit mystified by your mirror hitting issues, I don't see any cause for that on my example. If yours is a later example with an auto pin protruding from the back that would be prime culprit for me...
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03-19-2014, 04:58 PM   #4
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mine has 5 mm max protruding from the back of the M42 thread, a lot less than many of the other M42 lenses I've got.

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