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Pentacon Prakticar 50mm f/1.8 converted to P/K mount
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PostPosted: Sat Aug 06, 2011 4:16 pm    Post subject: Pentacon Prakticar 50mm f/1.8 converted to P/K mount Reply with quote
I received this from iangreenhalgh1 the other day and chucked into a lathe to modify the mount to fit my Pentax DSLR's. It fits like a charm. The aperture indicator line is directly on 12:00 o'clock and the locking pin snaps right into place. The only drawback is the register distance. Not quite infinity focus. But anywhere around 25 feet makes it a very sharp little portrait lens. Thanks ian!!!

A few photos with it......







PostPosted: Sat Aug 06, 2011 5:12 pm    Post subject: Reply with quote
Nice work! Shame about the infinity issue, pity when Praktica copied the K mount they didn't copy the register as well.


PostPosted: Sat Aug 06, 2011 6:49 pm    Post subject: Reply with quote
iangreenhalgh1 wrote:
Nice work! Shame about the infinity issue, pity when Praktica copied the K mount they didn't copy the register as well.


I have done a similar modification to a Vivitar series1 70-210 group 2 Tokina made lens with a C/Y mount. It does give infinity focus. I'm not disappointed with the Prakticar at all. Like I said a very nice portrait lens.

Thanks again my friend.


PostPosted: Sat Aug 06, 2011 8:45 pm    Post subject: Reply with quote
I have that lens in OM mount and it disappointed me after an initial test, didn't seem as sharp as my cheapo Optomax 200mm. I need to try it out more, I suspect there is an issue with the OM-EOS adapter as my 1.8/50 Zuiko seemed pretty soft at infinity unless stopped down, probably the adapter is a mite too thick.

Enjoy the Pentacon, I love my copies, all 5 of them, having 6 was just greedy! It's an extrememly common lens in the UK and it seems only recently are people realising it's a lovely piece as prices are still very low.


PostPosted: Sat Aug 06, 2011 10:02 pm    Post subject: Reply with quote
I wonder if the information that is available about the various register distances is correct for the Praktica bayonet ?

I 've got a very nice Sigma Superwide 24mm lens that had Praktica B mount, and I wanted it to fit PK.
I'm and engineer, I have a lathe in my workshop so I did the calculations and machined the required amount off the back of the lens, fitted the PK mount, and it's a bit like BigDawg's conversion.

I know that I machined the amount off that I set out to remove, and although I can't find the bit of paper with the calculation on, I'm certain that I got the calculation right.

My lens is now very close focusing, at infinity the focus is about 18 inches away and at 0.6 feet it's about 4 inches. It's a good macro lens, but not what I intended. Rolling Eyes


PostPosted: Sun Aug 07, 2011 12:53 am    Post subject: Reply with quote
That mystifies me. I have a Pentax ME Super and several Prakticas here, I can try to measure the registers if you like, I think my dad has a micrometer screw gauge.

I have quite a few lenses that require some surgery to make them useable on EOS or PK, including several Sigma PB mount lenses and a pair of Pentacons - 1.8/20 and 2.8/28, if you guys can figure out the PB to PK conversion process we could breath new life into a whole load of lenses, might even persuade me to get a Pentax DSLR to use em all!

That Sigma 24mm is a really good lens, I had one badged Carl Zeiss in Minolta AF mount, should never have sold it!


PostPosted: Sun Aug 07, 2011 1:05 am    Post subject: Reply with quote
BD, it's very easy to adjust the infinity focus on this lens. Unscrew the label ring arount the front lens and inside there are three screws which clamp the focus grip to the helicoil. Slacken these and you can adjust the focus while keeping the grip hard against the infinity stop.


PostPosted: Sun Aug 07, 2011 4:53 am    Post subject: Reply with quote
peterqd wrote:
BD, it's very easy to adjust the infinity focus on this lens. Unscrew the label ring arount the front lens and inside there are three screws which clamp the focus grip to the helicoil. Slacken these and you can adjust the focus while keeping the grip hard against the infinity stop.


I've thought of that already. The front lens housing unscrews easily and the screws are right there under the front glass. I'll give it a try tomorrow and let you know how it works out.

Not as you described. With this lens the inside helical bottoms out at infinity and there is no room to move the lens set closer to the film plane or sensor plane. The screws you are talking about are not there on this lens. There are three screws but they fasten the aperture iris group to the base of the inside helical but that is all it does.

I've had it totally disassembled and there really is no way to get them closer.

The Practika register distance is 44.4mm and the Pentax K mount register distance is 45.46mm. It might be possible to move or shim the lens elements closer thus achieving infinity focus. I'll keep trying and see what develops.
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