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08-08-2011, 01:49 PM   #16
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QuoteOriginally posted by excanonfd Quote
Thanks Rio, if I see an Exacta or Praktica B lens cheap, I will definitely give this modification a try.
Topcon RE lenses have the same bayonet mount as Exakta. I can't guarantee this will work on Exakta lenses with the protruding-arm stop-down button; I tried converting one of those (FAIL!) but that may have been the lens' fault (stuck iris).

Praktica-B register is 44.4mm and so is theoretically do-able. But its bayonet is too wide for any M39-M42-PK adapter(s) to fit around. I have a Pentacon Prakticar 50/2.4 to modify, which will require removing the entire bayonet. Let's see... Hmmm, I thought I'd have to disassemble this from the front, but I now find I can easily pry a plastic ring off the back, revealing some screws.

[/me whips out screwdriver, does the evil deed]

Yeah, the bayonet came right off, no problem! If I clip off the aperture flag to keep it out of the way, it will work like an M42. Looks like I have two mount options: 1) glue a narrow-flange M42-PK adapter to the lens base; or 2) further disassemble to remove the contact pins; then grind off ~1mm+ from the outside of a flanged M42-PK adapter to fit inside the aperture ring, drill some holes, and screw it on the lens. (1) will be faster; 2) will be more secure. Darn, I'm running out of adapters.

[/me sets Prakticar next to Ricoh 35/2.8 awaiting adapter gluing...]

08-08-2011, 02:16 PM - 1 Like   #17
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hi guys, b-mount could still be found cheap, but i dont think for long.... there are 3/4 and eos adapters are available. anyway, this is a different topic.
Rio, i found this one might help you: http://www.electron.de/ebay/m42.pdf
cheers
08-08-2011, 07:20 PM   #18
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QuoteOriginally posted by alex1967 Quote
Rio, i found this one might help you: http://www.electron.de/ebay/m42.pdf
And a +Like for you! Thanks, this is very helpful. I haven't seen such an M42 adapter; the wide-flanges M42-PK adapter is about 2mm too wide to fit on the lens base, so I'll need to grind off 1mm from all around. Hmmm, how to do that... try to clamp the adapter into an electric drill and run it against rough sandpaper, I guess.
__________________________________________________________

EDIT - Addundum: Following those instructions, I successfully performed steps 1 (remove plastic ring), 2 (remove bayonet), and 3 (remove aperture flag). But then I attempted step 4 (remove base plate) -- mine has more screws, one of which seems to retain something critical. Loosening the screws allows removing the base plate, but the aperture ring falls off also, with nothing to restrain it. Re-tightening those screws caused the aperture ring to seize. Those screws should probably be held in with a drop of contact cement on each if no further modification is tried.

I need to scrap the idea of using a wide-flanged M42-PK adapter screwed down. That leaves the option of gluing a narrow-flanged M42-PK adapter to the base plate. But I tried a test fitting -- adapter on camera, lens pressed against it -- and found that the lens won't fit close enough for infinity focus. The aperture ring would need to have about 1mm ground off it, AND the base plate removed. And I won't go that far.

I don't need another close-focus-only lens. (Far focus is just under 1m.) So I must rate this Pentacon Prakticar 50/2.4 as UNFIT FOR PK MODIFICATION. I guess I'll try to reassemble and resell this one. Let's see, where did I put all the pieces... ???

Last edited by RioRico; 08-08-2011 at 10:08 PM.
08-09-2011, 03:54 AM   #19
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Hi Rio, sad to hearings your misfurtune.
There were 2 versions of 50/4. http://www.praktica-users.com/lens/blenses/pp2.4_50.html
2nd version was also made in Romania. It was slightly bigger than DDR one... but also could also be different engineering wise ?????
Cheers

08-09-2011, 07:50 AM   #20
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Mine seems to have all-metal barrel, so it is probably a DDR version. I think the main difficulty, compared to the Meyer 135, is that the base is engineered differently. Perhaps someday when I feel more adventurous, I will try again. Thanks for your information!
08-09-2011, 09:24 PM   #21
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QuoteOriginally posted by alex1967 Quote
Hi Rio, sad to hearings your misfurtune.
There were 2 versions of 50/4. http://www.praktica-users.com/lens/blenses/pp2.4_50.html
2nd version was also made in Romania. It was slightly bigger than DDR one... but also could also be different engineering wise ?????
Cheers
In your original post, you stated that the Praktica B mount came with the lens, do you have a caliper or micrometer to accurately measure the thickness of the bayonet mount? It's a shame RioRico could not make the reversible conversion, although I had hoped that RioRico would succeed, I half-expected Praktica B to PK conversion would be non-reversible.

Thanks,
08-14-2011, 03:03 AM   #22
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QuoteOriginally posted by excanonfd Quote
In your original post, you stated that the Praktica B mount came with the lens, do you have a caliper or micrometer to accurately measure the thickness of the bayonet mount? It's a shame RioRico could not make the reversible conversion, although I had hoped that RioRico would succeed, I half-expected Praktica B to PK conversion would be non-reversible.

Thanks,
Hi mate, sorry belated. I'm travelling for biz now and will definitely post dimensions of the original b-mount on my return. Cheers, Alex
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