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The right type of M42-to-K-mount adaptor
Posted By: dosdan, 01-18-2010, 05:18 AM

There are two types of M42-to-K-mount adaptor:

  • The Flange type
  • The Recessed type

Don't be like me and get the wrong type, which is the Flange type. While the flange type is cheap, is commonly available and the flange appears thin, it is still thick enough to prevent focus at infinity.

Get the recessed type. I've got a "Roxsen" 3rd-party version. This is very easy to fit on a K100D Super body, but I find it is difficult to fit or remove this quickly on a K20D. The genuine Pentax M42 recessed adaptor is reported to be easier to fit compared to 3rd-party adaptors.


Here's some pictures I took showing the difference between the two M42-to-K-mount adaptors.

Recessed-type adapter plus insertion/removal key on left Flange-type on right. Both showing the side that fits to the camera:



Flange-type fitted:






Recessed-type fitted:


Dan.

Last edited by dosdan; 01-18-2010 at 12:53 PM.
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03-29-2018, 02:20 PM - 1 Like   #31
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QuoteOriginally posted by Theov39 Quote
Good point. No doubt it is just as confusing for them. This particular one was priced quite high so I thought it may have been a genuine.

A copy got stuck on my camera once so I am keen to get a genuine now if I can but the prices for new adapters are just crazy (eg BH Photo are selling them for US$75).
Like I say in my earlier posts in this thread, if it ain't the real one, take that spring off immediately and never look back. If you aren't sure whether it is genuine even after it is in your hands, take the spring off and put it on a body -- the real one will be pretty loose and move around, the fake ones will stay in there pretty firmly even without a spring. (If it is the real one, put the spring back on.) In practical usage, real ones go on the body and stay there, fake ones go on the lens (sans spring) and stay there.

07-25-2018, 11:36 AM   #32
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Can anyone comment on how much focus is lost with the non-infinity focus-able adapters? For example, will I still be able to focus out to 50 feet away or does it become a strictly macro only lens with such adapter?
07-25-2018, 06:59 PM   #33
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QuoteOriginally posted by stillshot2 Quote
Can anyone comment on how much focus is lost with the non-infinity focus-able adapters? For example, will I still be able to focus out to 50 feet away or does it become a strictly macro only lens with such adapter?
Depends on the lens -- 50ft *IS* infinity with many lenses. It is always closer than I want it to be though (with anything that isn't a macro already) so I don't like those adapters, but again, just depends -- with a telephoto you can get 10 or 20ft probably, but if you are trying to focus at near the limit it is just going to annoy you to no end. (Some adapters are thinner than others -- look for a flimsy-looking one if you get one.)
07-25-2018, 10:12 PM   #34
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QuoteOriginally posted by vonBaloney Quote
Depends on the lens -- 50ft *IS* infinity with many lenses. It is always closer than I want it to be though (with anything that isn't a macro already) so I don't like those adapters, but again, just depends -- with a telephoto you can get 10 or 20ft probably, but if you are trying to focus at near the limit it is just going to annoy you to no end. (Some adapters are thinner than others -- look for a flimsy-looking one if you get one.)
Ok thanks. I've also been thinking about readjusting the focusing range of the lens to go past infinity so with such adapter would end right at infinity but I'm not that knowledgeable on how to disassemble lenses in order to do so. I just want a permanent mount for a Takumar 200mm f5.6 and don't like the ones with the removable tabs so much..

07-25-2018, 10:25 PM   #35
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QuoteOriginally posted by stillshot2 Quote
Ok thanks. I've also been thinking about readjusting the focusing range of the lens to go past infinity so with such adapter would end right at infinity but I'm not that knowledgeable on how to disassemble lenses in order to do so. I just want a permanent mount for a Takumar 200mm f5.6 and don't like the ones with the removable tabs so much..
Well... good idea to learn to like them -- just stick it on there (remove spring on adapter) and make it a semi-permanent bayonet. I've got at least a dozen like that -- the friction fit is usually more than adequate as long as you don't forget that's how it is attached (and your focus isn't so stiff that it rotates the lens off the camera).
07-26-2018, 07:53 AM   #36
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QuoteOriginally posted by stillshot2 Quote
Can anyone comment on how much focus is lost with the non-infinity focus-able adapters? For example, will I still be able to focus out to 50 feet away or does it become a strictly macro only lens with such adapter?
The formula for the maximum focus distance is a very strong function of focal length. The formula is:

MaxDist = f*(2+f/∆+∆/f), where ∆ is the flange thickness in mm and f is the focal length in mm

So, if the flange is 1 mm thick, the maximum focus distance for some different lenses would be:

28mm: 2.8 feet
50mm: 8.5 feet
100mm: 33.5 feet
200mm: 132 feet

Note that these numbers change a lot if the lens can focus past infinity.
07-26-2018, 01:02 PM   #37
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QuoteOriginally posted by vonBaloney Quote
the friction fit is usually more than adequate
Sadly, the focusing ring on this lens is just a little too stiff for the mount to have a good enough friction fit. I do have two other lenses that work ok with the infinity adapters attached and with the springs removed though.

QuoteOriginally posted by photoptimist Quote
200mm: 132 feet
Thanks for the calculations! I think 132 feet could be enough for me. May try it out
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