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CZJ 20/2.8 Flektogon dissected
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PostPosted: Thu Apr 15, 2010 12:39 pm    Post subject: Reply with quote
The hidden tightening ring round the front element is very important. This is how the infinity focus is adjusted on this lens. This picture explains (thanks to Indianadinos for pics of his lens):



As you see, turning the filter ring will adjust the infinity setting, so it's important that the clamping ring is very tight. Never grip the filter ring when you mount and and dismount this lens - always grip the focus dial only, or the lens body behind it. Here is another shot of the clamping ring behind the front element.



If the filter ring becomes loose, it can turn too far and the optical block comes away completely from the lens body, as Anu found. Replacing it is not too difficult but you have to remove the mount and loosen this clamping ring, then when all is back together you need to reset the infinity focus all over again before tightening the clamping ring.


PostPosted: Thu Apr 15, 2010 4:21 pm    Post subject: Reply with quote
peterqd wrote:
The hidden tightening ring round the front element is very important


Thank you for the pictorial instruction. I just noticed I need to reopen the damn lens once more - not only is the distance scale wrong, but also there is now severe decentering. Still, the lateral chromatic aberrations are basicly all gone, so something is just right now with the lens.


PostPosted: Thu Apr 15, 2010 8:00 pm    Post subject: Reply with quote
Anu, when you have the lens ready to reassemble, make sure the focus dial is at the minimum distance stop. Then you can screw the optical block in a little way before the legs need to be located in the slots and once these are correct you can screw the block all the way in. Make sure you have the legs the correct way round, I think this might be where you went wrong. The aperture operating mechanism has to be on the opposite side of the lens to the index mark.


PostPosted: Thu Apr 15, 2010 8:22 pm    Post subject: Reply with quote
Well, this is a really useful thread Wink ...

I have finally managed to screw in the optical group of my Flek 20/2.8, and i was asking myself how the infinity focus could be adjusted ...

peterqd wrote:
The aperture operating mechanism has to be on the opposite side of the lens to the index mark.


Yes, yesterday i had to unscrew back the optical group because of this ... The f/stop scale was on the opposite side wrt the red mark ...

Thanks to all for sharing the info and the pics ...

Cheers

P.S.: To Peter: looking at your picture, i suppose i have to remove the name ring to access the focusing adjust clamp ...

Last edited by indianadinos on Thu Apr 15, 2010 8:25 pm; edited 1 time in total


PostPosted: Thu Apr 15, 2010 8:24 pm    Post subject: Reply with quote
peterqd wrote:
Anu, when you have the lens ready to reassemble, make sure the focus dial is at the minimum distance stop. Then you can screw the optical block in a little way before the legs need to be located in the slots and once these are correct you can screw the block all the way in. Make sure you have the legs the correct way round, I think this might be where you went wrong. The aperture operating mechanism has to be on the opposite side of the lens to the index mark.


Thank's for the tips - I need to reread it tomorrow. Over the last hours my frustrations grew and I was tempted at throwing the darn thing out of the window. Well, didn't do that. I managed to cure the decentering and now left and right are equals - also managed to clean one spot in tbe center of a small element I had not noticed earlier. The only thing left is adjusting the focus, at least I hope so.

I think that the only flaw earlier on, before I started the never ending disassemble-assemble-cycle, was that the hidden tightening ring wasn't actually on it's screw properly, but one side was slightly elevated. This evidently was enough to dislocate the first group a bit creating the decentering.

Ah well, tomorrow evening I'll try to finnish the job. I have the gut feeling, that it'll take a bit longer than one more evening to get the lens into proper shape...

If you have any more tips, I'm happy to listen. And I think that the information you have provide so far should be stored somewhere - maybe there should be a MFlenses-wiki for repair instructions...


PostPosted: Thu Apr 15, 2010 9:12 pm    Post subject: Reply with quote
indianadinos wrote:
P.S.: To Peter: looking at your picture, i suppose i have to remove the name ring to access the focusing adjust clamp ...

Yep, and it's a big one! Smile I found a lid from a jam jar which just fitted inside the filter ring and I used a piece cut from an old rubber glove to give the friction. Mine came out quite easily.

I've often found loose lens rings on CZJ lenses. It can cause all sorts of weird effects if the glass isn't seated properly. When you have a lens apart it's a good idea to check all the lens rings for tightness.

Great to hear you got it all back together Anu. It isn't difficult once you know the trick. The way this lens is adjusted is unique in my experience, I've never seen one like it before. By the way, there is a trick you can use to adjust the infinity setting. With the filter ring/lens block screwed right in and the focus dial at the infinty stop, tighten the clamping ring gently, enough so that it just grips enough to stop the filter ring turning. Then turn the focus dial slowly until infinity comes into focus and put a pencil mark on the filter ring against the infinity mark on the focus dial - I don't mean the index mark. Now loosen the clamp again, return the focus dial to the inifinity stop and then turn the filter ring slowly to line up the pencil mark with the index mark. When it is accurate you can give the clamp its final tightening. It takes several tries to get it perfectly accurate so have a tin of patience on your desk! Smile


PostPosted: Fri Apr 16, 2010 7:57 am    Post subject: Reply with quote
peterqd wrote:
indianadinos wrote:
P.S.: To Peter: looking at your picture, i suppose i have to remove the name ring to access the focusing adjust clamp ...

Yep, and it's a big one! Smile I found a lid from a jam jar which just fitted inside the filter ring and I used a piece cut from an old rubber glove to give the friction. Mine came out quite easily.

I've often found loose lens rings on CZJ lenses. It can cause all sorts of weird effects if the glass isn't seated properly. When you have a lens apart it's a good idea to check all the lens rings for tightness.

Great to hear you got it all back together Anu. It isn't difficult once you know the trick. The way this lens is adjusted is unique in my experience, I've never seen one like it before. By the way, there is a trick you can use to adjust the infinity setting. With the filter ring/lens block screwed right in and the focus dial at the infinty stop, tighten the clamping ring gently, enough so that it just grips enough to stop the filter ring turning. Then turn the focus dial slowly until infinity comes into focus and put a pencil mark on the filter ring against the infinity mark on the focus dial - I don't mean the index mark. Now loosen the clamp again, return the focus dial to the inifinity stop and then turn the filter ring slowly to line up the pencil mark with the index mark. When it is accurate you can give the clamp its final tightening. It takes several tries to get it perfectly accurate so have a tin of patience on your desk! Smile


I had to open the lens again, as I had earlier adjusted the infinity adjustment screw that's inside the lens (the same place the "legs" are held by screws). After this, all hell broke loose and suddenly only the center was sharp and both edges were worse than ever. Luckily some front lens cleaning did the trick and at least the initial test shots are very, very promising. I need to do some outdoor tests when I have time, but so far so good.

Thank you again for your guidance!

I think you should write a small guide regarding this and general CZJ 20/2.8 service (and including the internal focus adjusting screw), as there are lots of badly adjusted Flektogons out there.

Oh, that jam jar trick is neat. I need too remember that Smile


PostPosted: Fri Apr 16, 2010 12:33 pm    Post subject: Reply with quote
I celebratedd too early. The test shots revealed that the lens has never been this bad... aaaaaargh... I am sure yet another weekend will go into trying to fix the lens and in the end I'll fail, I am sure.


PostPosted: Fri Apr 16, 2010 2:23 pm    Post subject: Yahoo Reply with quote
At last Smile

I found a nasty little smudge in one of the back elements I had 'cleaned' Wink

Now the lens delivers and I just adjusted the infinity to be right.

Thank you a lot for the help!

Edit:

Well, infinity isn't quite right yet, but that's not a problem. Image quality is very similar to what it was before the disaster struct - the CA is back to what it was back then Sad

I guess I'll be opening the damn thing a few more times to check if I can improve the IQ as for a brief moment it was superior to what it is now.

I am also wondering - how much CA do folks have on their Fleks? (I use LR 1.41 and the sliders are -40 and -10 or so.)
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