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m49 0.5 to 0.75 filter thread adapter ring?
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PostPosted: Sun Jan 14, 2018 10:43 pm    Post subject: m49 0.5 to 0.75 filter thread adapter ring? Reply with quote

I just purchased a Mir 1 silver/white grand prix m39 lens...While waiting on it to be delivered I read that it is an atypical thread pitch? Is this true? m49 x 0.5? I'm getting some conflicting information. The auction said 0.75 but historian sites say 0.5. The logo on the lens is KMZ (but no red P, it is stamped grand prix, so it's not the earlier model).

I'm trying to do as much research as I can, but I'm coming up short. It's rather confusing between the various models (which makes me worry for other reasons as well).

Does anyone know of an adapter or step up ring of the sorts to convert it to something more usable with modern filters?

Thanks!


PostPosted: Mon Jan 15, 2018 10:20 am    Post subject: Reply with quote

I think you might be adding to the (my) confusion as you mention M39 at one point and M49 at another.
M39 filters are normally 0.5 pitch & M49 are normally 0.75.

I know M42 was used at both 1mm & 0.75mm thread pitches the latter usually called T2 (but some e-bay adapters just call it 'm42' even though this is the usual term for the 1mm pitch)

Some sources claim LTM thread is often described as M39x1mm but is actually M39 at 26tpi (a weird combination of standards)

M39 filter threads are normally M39x0.5 while M49 filters are normally M49x0.75
Most filter threads follow a standard pitch for their diameter though for M37.5 both 0.5 & 0.75 are used.

From the filter listings I've found

size standard pitch
m13.5 x0.5
m19 x0.5
m22.5 x0.5
m25.5 x0.5
m27 x0.75
m28 x0.75
m30 x0.75
m30.5 x0.5
m34 x0.5
m37 x0.75
m37.5 x0.5
m37.5 also x0.75
m38 x0.75
m39 x0.5
m40.5 x0.5
m43 x0.5
m43 x0.75
m46 x0.75
m48 x0.75
m49 x0.75
m52 x0.75
m55 x0.75
m58 x0.75
m62 x0.75
m67 x0.75
m72 x0.75
m77 x0.75
m82 x0.75
m86 x1
m95 x1
m105 x1
m112 x1.5
m122 x1

There are companies like GRB & RAF cameras that will custom make adapters like this if required.


PostPosted: Mon Jan 15, 2018 2:29 pm    Post subject: Reply with quote

Ah I see, sorry about that. I was describing the lens with m39 - mount. From what I read there was a difference in the mir 1 lenses. But I’m getting conflicting info from various places. I guess I won’t really know until I get the lens (though not sure how I could tell the difference other than seeing how a filter goes on maybe), but the last thing I want to do is cross thread or strip something.

I ended up finding raf. I don’t know if I should buy one now, they seem to only have one in stock. They’re $30. Hate to buy something I don’t need of course.

This was one of the sources of confusion. http://camera-wiki.org/wiki/Mir-1 ... the one I got is an earlier model, though I’m unsure if it’s the same as they talk about because so many variants were made or different factories used from what I can tell.


PostPosted: Mon Jan 15, 2018 5:48 pm    Post subject: Reply with quote

tom_m wrote:
Ah I see, sorry about that. I was describing the lens with m39 - mount. From what I read there was a difference in the mir 1 lenses. But I’m getting conflicting info from various places. I guess I won’t really know until I get the lens (though not sure how I could tell the difference other than seeing how a filter goes on maybe), but the last thing I want to do is cross thread or strip something.

I ended up finding raf. I don’t know if I should buy one now, they seem to only have one in stock. They’re $30. Hate to buy something I don’t need of course.

This was one of the sources of confusion. http://camera-wiki.org/wiki/Mir-1 ... the one I got is an earlier model, though I’m unsure if it’s the same as they talk about because so many variants were made or different factories used from what I can tell.


That suggests the model 1 has a different pitch to the model 1B, where the standard 49x0.75 is used.

To check the pitch when the lens arrives try a significantly smaller diameter male thread of known pitch (a machine screw will do) against the threads. If the threads consistently interlock the pitch is the same. If the threads get out of step the pitches differ. IMO this works out easier than trying to measure them or count the number of threads in 5mm & then using maths to work out a more accurate distance for one thread.