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09-09-2015, 01:55 PM   #1
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Praktica 42mm screw thread to K mount?

I found a Sigma 70 - 250 Zoom Macro lens at the DAV this afternoon in like new condition and bought it and a Coastar f2.8 28mm prime for $25 with my senior discount.
The Coastar is a K mount and went right on my K50 and seems to work just fine.
The Sigma is an M42 mount, but for a Praktica. It's not a highly rated lens but what the heck. Which is the best adapter to attach permanently to this lens? I found the Fotodiox adapter on Amazon for $13. Can I disable the spring so that it stays with the lens? Should I use a drop of Locktite 242 thread locker (the service removable type) What do I do about the aperture pin, attack with my Dremel?
Thanks folks,

09-09-2015, 02:23 PM   #2
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In Japan the "Pentax screw mount" is called the "Praktica screw mount". Both are the same thing, M42.

The aperture pin should be left alone. If the lens has the A/M switch you don't have to worry about it at all, if it an Auto only lens you will have to find a way to keep it pressed down.

If you buy one of the cheap adapters you should remove the spring in any case.
09-09-2015, 02:36 PM   #3
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Most of my lenses are M42, and I do exactly the type of adaptation that you've described. I remove the spring clip from the adapter and use a drop of Loctite to make the lens into a semi-permanent K Mount. Friction alone is enough to keep the lens securely mounted on the camera, so there's no need to get destructive and cut a notch for the locking pin. Make sure you use the non-flanged type of adapter so that you get infinity focus.
09-09-2015, 02:49 PM   #4
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Some people like to buy a cheap adapter and then remove the spring, and use something to attach the adapter permanently to the lens. But I would advise against that, unless you really test out the adapter first and make sure it is machined well enough. Sometimes cheap adapters are not machined well and they can get stuck on the camera mount, they can have sharp edges, or tolerances that are too tight or not tight enough. Some cheap adapters have a flange/collar, which can prevent normal infinity focusing with most lenses. m42 lenses also sometimes do not screw in properly into these adapters - you screw it in all the way, but it will be rotated to a side, instead of the top part being on top.
This is why i always recommend using the genuine adapter, non-permanently on the lens. This will also keep the value of the lens, as you can sell it off in its original state (though, I guess this is not important in this case). The genuine adapter costs a little more, but you can use it safely with many different lenses.
Anyway, there are plenty of threads about m42 adapters. I think there are even some tutorials on how to make it permanent. Feel free to search for those.
Here is a tutorial on how to use m42 lenses:
I usually link to this one, but there are others as well.

Many of us on this forum enjoy using m42 lenses, as well as other adapted lenses. When buying a lens, you usually want to get a good look at its mount, so you can see what it is. m42 is generally easy to identify. Main confusion can arise from some similar T adaptall, and m39, m37 mounts.
And congrats on the nice catch of lenses. Maybe this will lead you to other m42 gems

09-09-2015, 06:30 PM   #5
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Thanks, Guys. I was examining the Sigma lens and found I got an extra bonus. It had a Hoya UV(0) filter attached and it's the same 62mm diameter as the Coastar. Unfortunately I've tapped out that DAV store and I haven't found any more lenses at their other locations here in Wichita. I should probably lay off for now anyway if I want to keep my wife happy (I bought an new LED light fixture for the hallway and installed it before she got home from work. If I paint the hall tomorrow I should have enough points stored up to go see Fifi a week from Saturday.)
09-09-2015, 06:48 PM   #6

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QuoteOriginally posted by Na Horuk Quote
But I would advise against that, unless you really test out the adapter first and make sure it is machined well enough.

Good advice, and I'd recommend testing a dubious adapter in the female end of a K-mount extension ring or the like, not a good camera.

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