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Fine-tune your PB Prakticar 2.8/28mm for EOS FF
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PostPosted: Sat Mar 31, 2012 12:32 pm    Post subject: Fine-tune your PB Prakticar 2.8/28mm for EOS FF Reply with quote
In order to lower the prices of Prakticar 28mm on Ebay (to buy them all myself) i will describe the six reason why there is a chance your sample won't produce optimal results Wink.

Besides standard issues like dust, haze and fungus (which has to be said aren't really problematic here), rear lens system (with 4 elements!) has 6 little screws for fine-tuning. Not three like Orestegon 29mm, but six. Three for the whole rear system like with 29mm and additional three for last group. Any of these screws can be responsible for causing the blur by allowing lens group to move away from optimal position. Besides they (little screws) are very prone to break on top and one has to drill through them in order to insert replacement.

Exaggerating of course, but relly if your sample is sharp wide open forget about cleaning some insignificant particles, removing some starting edge fungus or so. Better use the lens as it is, you might never achieve the same results again.

Anyway for the lens to be EOS 5DmkII friendly some other stuff has to be done:

- adjusting infinity: try to get metal version with three little screws on outside of focusing ring; if later lens version then one has to reach focusing ring holders from top which involves very probable damaging of plastic label ring
- removing auto lever
- removing electric contacts (optional)
- adjusting wide-open aperture position (in most cases aperture doesn't fully open if auto lever isn't accessed by Praktica PB camera; the overlapping is minimal but one loses perfect circle bokeh)
- trimming of last protruding part and painting it matte black

And finally: lens has Zeiss Jena signature all over it (or better inside of it) - being very similar to F2.4 Flektogon.

Some photos:

Front filter holder and label ring removed:


Three screws for adjusting infinity (later version):

http://fc07.deviantart.net/fs71/f/2012/083/e/3/10_by_juredolzan-d4tr7qn.jpg

Removing auto lever and electric contacts:






Off with the aperture ring:


Remember the Orestegon?


Rear part:


3x2 little screws:


Back together (no mount yet):


Sample photos were posted here: http://forum.mflenses.com/contax-distagon-2-8-28-vs-jena-2-8-28-t46845,start,15.html


PostPosted: Mon Sep 23, 2013 8:58 pm    Post subject: Reply with quote
Thank you! My version (Pentacon Prakticar 28/2.Cool has the 98% same design as CZ Jena. The only exception is infinity adjustment screws in the front - unlike yours three, mine has only one very small screw... and the Pentacon label of course. The rest is totally the same.


PostPosted: Mon Sep 23, 2013 9:13 pm    Post subject: Reply with quote
It's not a CZ Jena lens design, only the last production after the end of the GDR was marked CZ Jena, most of them are labelled Pentacon, which is who designed and built them. Construction is very similar to the Pentacons 1.8/50 and 2.8/135.


PostPosted: Mon Sep 23, 2013 9:29 pm    Post subject: Reply with quote
iangreenhalgh1 wrote:
It's not a CZ Jena lens design, only the last production after the end of the GDR was marked CZ Jena, most of them are labelled Pentacon, which is who designed and built them. Construction is very similar to the Pentacons 1.8/50 and 2.8/135.


You 're right Ian, 28, 50 and 135 Prakticars' barrells have common concept created by Pentacon. However, I'm not stating it's genuine CZ design, just Pentacon Prakticar is similar to CZJ Prakticar.
Any ideas wthether optic scheme is of CZJ origin?

BTW I'm new here and since there is no newbies thread I want to say hello to MFlenses community Smile

Regards,
Alex


PostPosted: Mon Sep 23, 2013 9:36 pm    Post subject: Reply with quote
Hi Alex, welcome. Smile

I'm not sure where the design originated from. it might be a development of the earlier 29mm. Jena did have a 28mm design but it was an f2 and never produced for SLRs as it was too complex and therefore expensive.

I'm in the middle of converting 28, 50 and 135 Pentacons to Nikon, having two copies of each, I figured why not, cheaper than buying Nikkors. Smile


PostPosted: Mon Sep 23, 2013 9:59 pm    Post subject: Reply with quote
I've safely converted 135 to Canon, without destroying PB mount so that the conversion may be reversed and about to finalize 50mm Prakticar.

28mm Prakticar conversion to Canon made me stuck for a while due to the mirror collision, however, I think I will resolve it sooner or later. Also, I've reached a person who has already converted 28mm Prakticar to Nikon bayonet successfully - with infinity and without mirror cllision.

Nikkors are good too, but way more expensive Smile Pentacons lately are being thrown out to a market for peanuts. I've bought 28 for 5GBP and 135+50 for 15GBP. I'd be happy to have more of them Smile


PostPosted: Mon Sep 23, 2013 10:07 pm    Post subject: Reply with quote
mosaster wrote:
iangreenhalgh1 wrote:
It's not a CZ Jena lens design, only the last production after the end of the GDR was marked CZ Jena, most of them are labelled Pentacon, which is who designed and built them. Construction is very similar to the Pentacons 1.8/50 and 2.8/135.


You 're right Ian, 28, 50 and 135 Prakticars' barrells have common concept created by Pentacon. However, I'm not stating it's genuine CZ design, just Pentacon Prakticar is similar to CZJ Prakticar.
Any ideas wthether optic scheme is of CZJ origin?

BTW I'm new here and since there is no newbies thread I want to say hello to MFlenses community Smile

Regards,
Alex


Some say SIGMA mini-wide (not newer II), which focused to 0.22m. I cannot confirm it, also do not own it.
But PENTACON never was a good wide angle lens maker, more experience for tele-photo varieties.
I should buy one of Sigma mini-wide cheaply and disassemble one to look the optical design.


PostPosted: Mon Sep 23, 2013 10:07 pm    Post subject: Reply with quote
iangreenhalgh1 wrote:
Hi Alex, welcome. Smile

I'm not sure where the design originated from. it might be a development of the earlier 29mm. Jena did have a 28mm design but it was an f2 and never produced for SLRs as it was too complex and therefore expensive.

I'm in the middle of converting 28, 50 and 135 Pentacons to Nikon, having two copies of each, I figured why not, cheaper than buying Nikkors. Smile


I guess it was F2.4?


PostPosted: Tue Sep 24, 2013 10:26 am    Post subject: Reply with quote
koji wrote:
iangreenhalgh1 wrote:
Hi Alex, welcome. Smile

I'm not sure where the design originated from. it might be a development of the earlier 29mm. Jena did have a 28mm design but it was an f2 and never produced for SLRs as it was too complex and therefore expensive.

I'm in the middle of converting 28, 50 and 135 Pentacons to Nikon, having two copies of each, I figured why not, cheaper than buying Nikkors. Smile


I guess it was F2.4?

Yes and, afaik, made with floating elements in the last years of the GDR.


PostPosted: Tue Sep 24, 2013 10:33 am    Post subject: Reply with quote
I was thinking of the Visiogon 2/28:

http://www.ebay.co.uk/itm/Visiogon-f-2-28mm-Lens-block-optical-part-/160805822765


PostPosted: Tue Sep 24, 2013 1:01 pm    Post subject: Reply with quote
Could that Visiogon possibly be a projection lens? With no aperture incorporated and large opening, such possibility is there... AFAIK, post wwii Zeiss Jena did not have any 28mm for 35mm camera in serial production, they had 25's, 35's only. Those Pentacon 28mm could be some what related to the earlier 29mm, and that again could be related to the early 30mm, purely speculation, not proven...
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