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My adventures with the CZJ 20/2.8 Flektogon
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PostPosted: Tue Oct 06, 2009 1:21 pm    Post subject: My adventures with the CZJ 20/2.8 Flektogon Reply with quote
A couple of weeks ago I bought a mint Carl Zeiss Jena 20/2.8 Flektogon. At first the image quality was quite all right, but not worth the reputation it had; for example there was quite a bit of CA, and even stopping it down never made the corners good.

I though, ok, it only cost me 150€.

Well, then I attached a really bad lens hood into it and after a while I unscrewed the hood from the lens and oops, the front group loosened a lot and I even ended up removing it by accident. AAAAAAARRRRGGGHH - that was the loud sound that probably alarmed my neighbours. The next many hours I tried to fix it, but ended up losing infinity constantly. The next day I understood, that the lens had been improperly put together when I got it - I had to adjust the infinity the proper way to get it to focus right when the front piece was tightly in it's place. My conclusion was that the lens had left the factory with focus incorrectly calibrated, and then someone had recalibrated it by loosening up the front elements a bit - rather silly solution.

Now, it works fine. Or to be more precise, it works way better than just fine, even wide open. It is yet another stunning lens made by CZJ. On a 1.5x crop-sensor camera the lens is very sharp in the center wide open, and still perfectly usable even in the extreme corners! I was really amazed to realize how fantastic it turned out to be after little fixing.


PostPosted: Tue Oct 06, 2009 2:29 pm    Post subject: Reply with quote
Happy End! Congrats! I think this lens was cleaned too and perhaps it lost MC layer this is reason of CA , but I am unsure.


PostPosted: Tue Oct 06, 2009 4:11 pm    Post subject: Reply with quote
Attila wrote:
Happy End! Congrats! I think this lens was cleaned too and perhaps it lost MC layer this is reason of CA , but I am unsure.


Yes, a very happy end Smile Thank you.

I am not sure if removed MC should really increase CA much at all - after all CA is about different wavelengths hitting the sensor in different places, as you know. MC should just reduce air-glass reflections, thus increase contrast, I think. But I am known to think wrong, so no bets should be placed based on my opinion Smile


PostPosted: Tue Oct 06, 2009 7:44 pm    Post subject: Re: My adventures with the CZJ 20/2.8 Flektogon Reply with quote
Hi,

Anu wrote:

Well, then I attached a really bad lens hood into it and after a while I unscrewed the hood from the lens and oops, the front group loosened a lot and I even ended up removing it by accident.
[snip]
I had to adjust the infinity the proper way to get it to focus right when the front piece was tightly in it's place.
[snip]
Now, it works fine.


I did almost the same mistake as you, but with an UV filter instead Crying or Very sad Crying or Very sad Crying or Very sad ...

How did you manage to fix the infinity focus ? I have been able to fix infinity on my Tak 24/3.5 by adjusting the focusing helicoid, but the Flek 20/2.8 seems to be built in a different way ...
Did you use the trick of the second camera focused to infinity ?

Cheers


PostPosted: Wed Oct 07, 2009 12:06 am    Post subject: Reply with quote
I did the same thing too...than I opened lens in two pieces, and I couldnt fix it that it wouldnt go past the infinity. Please help me repair that...

Here is some info but only on back part, focus correction should be done on front part of the lens
http://repairnotes.wordpress.com/2009/09/17/flektogon-20mm-disassembly/


PostPosted: Wed Oct 07, 2009 6:55 am    Post subject: Re: My adventures with the CZJ 20/2.8 Flektogon Reply with quote
indianadinos wrote:
Hi,

Anu wrote:

Well, then I attached a really bad lens hood into it and after a while I unscrewed the hood from the lens and oops, the front group loosened a lot and I even ended up removing it by accident.
[snip]
I had to adjust the infinity the proper way to get it to focus right when the front piece was tightly in it's place.
[snip]
Now, it works fine.


I did almost the same mistake as you, but with an UV filter instead Crying or Very sad Crying or Very sad Crying or Very sad ...

How did you manage to fix the infinity focus ? I have been able to fix infinity on my Tak 24/3.5 by adjusting the focusing helicoid, but the Flek 20/2.8 seems to be built in a different way ...
Did you use the trick of the second camera focused to infinity ?

Cheers


You need to open the rear cover of the lens, remove the two thin metal parts on the booth sides (both connected with two screws). That is 3 long screws to open the back, 4 small screws to remove these "wide sticks". Whatever can be taken apart just by lifting without any tools , take it apart (don't remove the lenses from their places - you might want to make sure they're tightly screwed in though). You will find a tiny screw that does not connect anything anywhere (it is the one screw that is placed on different "orbit" compared to the other screws) - that screw is a focus stopper. Remove it. Then place the last thing you removed back into it's place, screw it in as much as it goes (without using too much force Smile ). With my m42 lens it took two full circles back from that position to get to the right focusing position - try that, and put the focus stopper screw back in it's place. Rebuild the lens and try if it works. If not, you need to open the lens up again from the back, and redo the infinity adjustment - try maybe three or one rotations instead of two.

Sorry I have not pictures and I'm drinking my first cup of coffee of the morning, so the describtion of the procedure is a bit messy.

But I assure you, that it is actually very simple procedure to do - it just may take some time, if you need to open the lens up a few times.

I hope this helps!

Oh, I think there is in the net images of CZJ135 disassembly, and if I recall right, it has the same focus adjustment mechanism.


PostPosted: Wed Oct 07, 2009 7:02 am    Post subject: Reply with quote
egidio wrote:
I did the same thing too...than I opened lens in two pieces, and I couldnt fix it that it wouldnt go past the infinity. Please help me repair that...

Here is some info but only on back part, focus correction should be done on front part of the lens
http://repairnotes.wordpress.com/2009/09/17/flektogon-20mm-disassembly/


Focus correction is done from the back! Or at least I didn't figure out any feasible way of doing it from front - if one just deals with focus problems by keeping the front elements loose (they should be tightened), the IQ will suffer and one might accidently remove the whole front group!
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