Pentacon 135 AUTO MC M42 infinity focus problem

gufo2k20 · Joined: 29 Jul 2013 Posts: 17

Hi all, i've recently bought a Pentacon 135 AUTO MC and immediately fell in love with his colour and natural looking images. Altough i've not needed yet , i've noticed it can't reach infinity focus. I thought was an adapter (Canon EOS - M42) thickness fault, but using it with a Jupiter 9 didn't show the same problem. The Jupiter 9 focus to infinity a bit before the focus ring stop.

The lens is the one on this thread http://forum.mflenses.com/pentacon-auto-2-8-135-partial-disassembly-and-cleaning-t9836.html

Do i need to disassembly the lens ad make a focus adjustement ? Is this a really hard operation or can i do it without removing apart every single lens piece?
Thanks in advance

peterqd · Expire: 2014-01-04

gufo2k20 · Joined: 29 Jul 2013 Posts: 17

Sorry for the link, really can't understand what am i doing wrong !!!!???? Confused

The message preview seemed fine....
Thks Moderator

peterqd · Expire: 2014-01-04

gufo2k20 · Joined: 29 Jul 2013 Posts: 17

Ok, understood.
thks again

I think my real name will be fine
Marco, Italy here

peterqd · Expire: 2014-01-04

sichko · Joined: 20 Jun 2008 Posts: 2528 Location: South West UK

Hi Marco

It's 5 years since I started the thread which you linked to - and the lens is long gone. However here's my best guess ...

You can't reach infinity so that you need to move the optical cell closer to the mount. The following might help ...

Disassemble the lens until you get to Picture 8 in the Link - the one after the picture of the aperture ring. Tape together the front two barrels - that is the front barrel contaning the glass and the middle barrel which carries the focussing grip - you will have to push forward the lens hood to do this. Remove the two screws holding the guide rod and the guide rod itself. Remove the infinity stop pin. Remove the tape (if it's there) holding the middle barrel (with focussing grip) and the back barrel (the one with the red focussing mark and the Depth of Field Scale) together. Looking it the back barrel rotate it clockwise (I think !) by one whole turn - and put everything back together gain. You may not be able to do this. It was possible on my lens but yours may be different. If it is possible the optical cell will be nearer to the mount by the thickness of the pitch of the thread which locks the two back rings together.

If it's not possible, or if it doesn't work, you may have to look for a thinner adaptor.

gufo2k20 · Joined: 29 Jul 2013 Posts: 17

Absolutely scared...... Shocked

Thk Peter, i'll check ASAP if there are screws under the filter flange.
John, the lens is exactly like the one you've disassembled in your "ancient" topic....
I'll try to do as you told me....hope to not mess up everything, or at least, i'll stop when not sure of what i'm doing.....
Thanks

gufo2k20 · Joined: 29 Jul 2013 Posts: 17

Ok, i e removed the focus stop screw....
Middle barrel still taped with the front barrel (the one under the hood).
Now, i'm not really sure of what i have to rotate together......
1) looking from the M42 screw, holding the front barrel (the one under the hood), rotate clockwise the focusgripped barrel and the focusmarked barrel together.....

2) what else.....???

Sorry for bothering you

gufo2k20 · Joined: 29 Jul 2013 Posts: 17

Here we are.....first, no success removing the front lens barrel (the screw is very stiff and without a first class screwdriver, i fear to make some damage....).
Same story for the filter's thread, so i don't know if there is a focus register under the front lens (but i don't think so....)
Also, it looks like this lens doesn't have any focus calibration on the main barrel....
The distance scale ande the focus ring barrels are screwed together, and the stop pin is between them. So, you can only screw or unscrew them by 1 turn or more (if possible...) before reinserting the the stop pin, obtaining to move in or out the optic-group once you reinsert the main helicoid.

I tried to make some rotations between the barrels, but i realized that i have no tollerance....between the distance scale / focus ring and also between the main helicoid / focus ring. So, no way to bring optics closer to the sensor plane....

Loosing the stop pin, i realized that infinity focus can be reached with very few degrees after the stop pin......about the infiniity symbol's lenght (2�~3� ??).
It seems this extra 2 or 3 degrees moves the optic oout of 0.2mm....
It's a very small distance so i'll try to polish down the adapter's thickness from
1.45 to 1.2~1.15 (just in case....)
Hope this works!!