Problem to disassemble Carl Zeiss Jena Tessar 2.8/50

[Spag]

Hey guys,

I bought today a Carl Zeiss Jena Tessar 2.8/50 for 8€. Problem: the focus ring only goes from 0.35m to 0.7m, and I can't focus between 0.7 and infinity. The focus ring is smooth, it just gets stuck at 0.7.

So I'm trying to disassemble it to see if I can fix the focus ring.

I've found a veeery nice guide to disassemble the lens:
http://oomz.net/tessar/

But I can't remove the focus ring (step 4). I guess I should unscrew it past infinity, but as it gets stuck at 0.7, can't do it.

Here's a shot from the lens, with focus ring stuck at 0.7 and infinity on the left.


Anyone got an idea what I could do to fix this nice lens?

Thanks!

[peterqd]

Without seeing the lens it's difficult to know exactly the problem, but it sounds as though someone has tried dismantling it before and not reassembled it correctly.

Does the front bezel round the glass turn when you rotate the focus dial?

[Spag]

I guess you're right. I just figured how to remove the focus ring, and you can screw it back many ways, I guess I just have to find the right position to screw it back so I can focus both ends. Right now I can focus from 0.35 to 1, so there's already some improvement.

[peterqd]

[Spag]

[Spag]

Okay I don't get it.

How can the focus ring do a 5/6 of a complete rotation of the lens, when I cannot screw the lens part in the focusing ring more than 4/6 of one full rotation?

(hope it makes sense, my english sucks)

Going to bed before I break the lens

[the_Suede]

Try removing nr.8 and THEN turn the lens unit into the barrel as far as it will go - this should be significantly more than 4/6 of a turn. When you hit mechanical stop of the thread or some thing else, back off until nr.8 fits onto the nr.23, which I guess is the guide "male" for nr.8 which should fit OVER the nr.23. You might be on the wrong thread now, I have no idea how far the front should protrude when set at correct infinity.
After remounting the nr8 so that it fits over the nr 23 you should be able to rotate the focusing barrel (ring) correctly.
If you cant get to infinity on the camera after reassembling the lens you have to do it all over again, but this time, MARK the pieces (outer barrel and the front of the lens) together at the angle where the lens innards come loose from the barrel. If you go past infinity then you have to find the next thread where the lens barrel fits the lens assembly clockwise. If you can't reach infinty, you have to find the next thread where the lens assembly fits counter-clockwise. Then try again.

Sorry, but if you don't know the original length of the lens from flange to front when focused at infinity or closest focus, then there's no easier way to do this than by redoing it until you get it right... But if you mark the position you know don't work, then it will be easier. Good luck!

[Spag]

Thank you Suede, but it looks like I hit thread stop at 4/6 of a turn... Tried to force past it but it just won't go further. And the thread doesn't look damaged in any way, so I really don't understand why am I unable to screw it past 4/6.

If I could find another model to compare with...

[peterqd]

If it helps, on my lens the helix turns one full rotation plus 1 hour, starting from the beginning of the thread. The screw 23 should be at the position of part 8 when the thread bites

[Spag]

Could an owner of this model post one/both of the following picture:

- from the side of the lens with focus set on infinity, so I could see how "deep" should I be able to screw the lens
- from the side of the lens with focus set on 0.35, so I could see how "far" comes the lens out of the focus ring

If I screw the lens starting from position where screw 23 is in position where 8 should be until thread stop, then turn focus ring to infinity before putting 8 back in place (matching perfectly with screw 23 position), I can only focus back to 0.4, after that the lens pops out of the focus ring.

Here's the lens screwed to the max (as if focused to infinity):


And here's the lens just before it pops of the screw (focused on 0.4):

[Spag]

Hmm well as seen on this other picture from a funtioning model, I guess something is wrong with the screwing thread on my lens..



But I can't find what's blocking the screwing thread. I'll try to bring it to my camera shop, see what they think.

[Spag]

Okay so I've found the problem...

There was a tiny screw stuck inside the focus ring, I had noticed it since the beginning, but it was stuck in a position I thought it was "there for a reason", so in a last try I thought "okay let's see what happens if I get rid of it". So now the lens is repaired! ^^

Another question though: There is dust inside the back lens, so I'd like to remove #19 and #20. Do I need a special tool to unscrew #19?



Yes, I do suck at mechanics!

[themoleman342]

You could get the right tool which is a lens spanner. They tend to be rather expensive for what they are. There have been some rather inventive methods to make one yourself in this forum. Just give it a search and you'll find them. I will warn you: cleaning the element is easy work but getting it back into place clean is somewhat more tricky. Especially for the smaller elements in the tessar. Unless it is an unnatural amount of dust I say skip it.

[Spag]

Okay thanks! Well the dust isn't that bad, and it looked pretty easy to remove the back lens... but I guess I'll pass for this time.

Next lens to clean: Pentacon 2.8/135 I bought for 5€. But the dust inside deserves to be removed this time.

[peterqd]

[Spag]

Thanks! And I need a real set of precision screwdrivers too!

[knox_br]

Sadly I need help to service this lens. =(

I just cant unscrew the 12 element from 11.



I´m using a lot of torque with my hands, but is just rock solid.

Any ideas?