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02-26-2012, 11:45 PM   #1
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Is M42 always M42 (registration distance question)

Till now, for me, M42 refers to the thread. Does it also 'define' the registration distance?

I have the opportunity to buy a wideangle Olympus M42 lens to basically complete my M42 kit. I wanted to buy it last month but ended up with some vet bills Want to pull the trigger now but realized last night that there is a possibility that the registration distance might be different. Better safe than sorry It will be used on a Pentax dSLR.

And is there anything else to pay attention to (e.g. rear element protruding into camera)? It's my understanding (from research on the web) that it works on a 5D Mk II without mirror issues.

Thanks in advance.

02-27-2012, 12:33 AM   #2
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I'm no expert on this, but as far as I know, an m42 is an m42, they're all the same with regards to register. I've never heard of one that has a different register. Don't take my word on it alone, if you're worried. I'm sure others will chime in on this.
02-27-2012, 03:25 AM   #3
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OK, I think I found the answer to the first question in wikipedia: M42 lens mount - Wikipedia, the free encyclopedia . The registration distance is defined in the specification.

So now the answer to the second one (if possible).
02-27-2012, 05:31 AM   #4
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The M42 X 1mm mount is indeed a universal mounting standard and the registration distance should always be 45.46 mm.

You may read more here:

M42 lens mount - Wikipedia, the free encyclopedia

02-27-2012, 06:39 AM   #5
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Some of the Olympus m42 have an additional pin on them as well that might be a small issue (from Camerapedia)

QuoteQuote:
Olympus Edit

Olympus made a small range of lenses in M42 mount, for their FTL body. There is a rumor saying that these lenses were not designed nor built by Olympus, and that they had nothing to see with the later OM lenses. However their characteristics are very similar to the equivalent OM lenses.

28/3.5
35/2.8
50/1.4
50/1.8
135/3.5
200/4

These lenses have an additional pin to lock them into place on the FTL body. On some other M42 bodies, this pin could prevent from mounting them.
02-27-2012, 08:49 AM   #6
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As others are saying, M42 is a standard mount, including the registration distance. There are however several other mounts using a 42mm thread that are not M42, but might be sold as such because the seller doesn't know. I don't think this lens is such a case though.

The only one you're likely to accidentally buy is probably T2, which has a 55mm registration distance and adapters to just about anything are readily available. T2 also uses a different thread pitch than M42, it won't mount smoothly in your adapter. Don't force it or you'll probably damage at least one of the adapter or lens.

(I also have two lenses using a T2 compatible thread but slightly longer registration distance, possibly using a system called Unidapter. They work well enough with T2 adapters, focusing a bit past infinity.)

Regarding the mirror, I don't think any M42 lenses have a problem on APS-C, but some do on full frame cameras with large mirrors. (The Kilfit Makro Kilar 40mm springs to mind.)

Last edited by drougge; 02-27-2012 at 08:50 AM. Reason: More info
02-27-2012, 09:30 AM   #7
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Thanks for the replies. I'm quite sure that the seller knows what he's selling (auto.zuiko 28/3.5, the first one that eddie1960 has in the list above) and I will meet him in person and take my camera with.

In this case I don't mind doing a bit of surgery if necessary with regards to 'the pin'.
02-28-2012, 02:21 PM   #8
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QuoteOriginally posted by drougge Quote
Regarding the mirror, I don't think any M42 lenses have a problem on APS-C, but some do on full frame cameras with large mirrors. (The Kilfit Makro Kilar 40mm springs to mind.)
The mirror clearance issue was an ongoing concern back-in-the-day and was often part of a lens review if clearance was a problem with certain bodies.


Steve

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