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How to center a blurred Carl Zeiss Jena Flektogon 35 2.4
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PostPosted: Thu Oct 31, 2013 8:10 am    Post subject: Reply with quote

I'll explain in pictures.

This is what my flektogon looks like. Maybe there are several different version that have different barrel design?


From the side it looks like this. I marked the three pieces of the lens body that can be detached from each other. If I disassemble the lens from the rear, I can easily remove the rear apron that holds the rear group and the aperture mechanism and then the focusing barrel also easily comes off (btw, this is a pain to put back the right way). But the front barrel that holds the front group is completely stuck, doesn't move in any direction and I don't see any screws or anything like that.


Here's the lens again from the front with the front element retaining ring removed. This is just about the only thing I can remove from the front. With this ring removed the front element falls out and I could then access the second element of the front group and remove it from the front group housing but there would be no point doing that because the group must be adjusted as a whole. I can just see those three screws through the little gap between the front barrel and the front group housing but no way to access and adjust them.


PostPosted: Thu Oct 31, 2013 8:32 am    Post subject: Reply with quote

For adjust front glass you are opening lens just from the front, nothing from the beck.
For re lubing you are going from the beck.
From cleaning iris you are going bought.

One more thing, some times the lest glass in front element group (the one closed to the iris) can be unscrewed. But in that case whole pictures made with such kind of lens is blurred.

So if you have problem just with the cornets you have just to adjust firs glass of firs element group.

Here is example how to dissemble whole lens, but you don't need to do that.
http://www.kolumbus.fi/uusilehto/img/lenses/zeiss/disass/slides/step5.html

When I get home I will try to make some pictures to explain you what you have to do, step by step.


PostPosted: Thu Oct 31, 2013 8:35 am    Post subject: Reply with quote

You need the remove this screw before unscrewing the front ring. After that you will see three screws holding the front element group.



PostPosted: Thu Oct 31, 2013 8:43 am    Post subject: Reply with quote

Yes, of course I did take that little screw out. Maybe the threads just got stuck together somehow, I don't know... Sad


PostPosted: Thu Oct 31, 2013 8:43 am    Post subject: Reply with quote

You are doing something wrong, first thing to dissemble from the front is name plate-ring. I think (I can't remember right now) the flektogon one goes altogether with front barrel, you market it like front group apron. Like calvin83 said.


PostPosted: Thu Oct 31, 2013 9:10 am    Post subject: Reply with quote

What I do is to focus the lens to it MFD. Then remove the screw and screw off the front group apron. After that you will see three screws holding the front element group.

My version is the red MC one but I think it is more or less the same for your version


PostPosted: Thu Oct 31, 2013 10:50 am    Post subject: Reply with quote

The ring with the engravings looks like it's screwed in but it doesn't go out. The whole barrel doesn't move either.


PostPosted: Fri Nov 01, 2013 2:45 pm    Post subject: Reply with quote

Hi all,
I would like to do the same with my Flek and I did manage to screw off the naming plate but I don't see any adjusting screws, can anybody help?
And I saw no screw on the side either. It is the electric MC version. Thanks.



PostPosted: Sat Aug 01, 2015 7:51 pm    Post subject: Reply with quote

Sorry for zombifying this thread but this issue is so widespread that solution should be present even with all uploaded pictures lost.

***

The side/corner sharpness should be good (very good with APS-C sensors) with Flektogon @f/8 or above. Also there shouldn't be one side noticeably sharper than the other one.

The most common cause for the issues mentioned above is loosened front element(s).

***

The fix (for earlier version of CZJ MC Flektogon 35/2.4 - with min aperture f/22)

#1 Unscrew the front name plate ring completely from lens' front inner screw. The best way is to use a specialized rubber tool. If the tool is not available simply use a M42 lens rear cap wrapped in a soft cloth. Press with the chosen tool against the name plate ring and unscrew it. Note: The name plate uses tight screw tolerances (unlike common sun shades). Thus the inner screw's dents, scratches or bent screw prevents the name plate from unscrewing completely.

#2 Tighten the loosened front element. This is done by tightening element's fixation ring. The fixation ring is clearly visible under the removed front name plate ring (it got two wrench slots at its perimeter). Use a common lens spanner wrench to properly tighten the ring - be careful and don't scratch any glass surface! Note: Don't use excessive force for tightening.

#3 Screw the name plate ring back.

#4 Enjoy your Flektogon

***

I suspect the fixation ring requires periodical re-tightening. So perform a check from time to time when you use your lens often.


PostPosted: Tue Oct 13, 2015 8:18 am    Post subject: Reply with quote

I wonder if this will work on a 2.8/20mm Flektogon i have which sits unused from a long time.

I gave it for servicing and cleaning but it was still bad.

on f2.8 it looks like this



and this is at f8



even stopped down it looks soft and glowing.


PostPosted: Tue Oct 13, 2015 9:07 am    Post subject: Reply with quote

I think this is more than just a loose front element. Maybe one of the elements is reversed or doesn't sit properly in its place. Or badly damaged surfaces (from cleaning, fungus, etc.)


PostPosted: Tue Oct 13, 2015 10:06 am    Post subject: Reply with quote

I can try to disassemble it myself but the glass is certainly clear and not damaged by fungus.
The technician who was servicing it told me that the optics was in it's correct place and nothing was swapped in or loose.
it can be a factory issue i guess or it is not that good lens wide open by default.

How sharp it can be wide open? maybe i'm expecting too much of it Smile


PostPosted: Tue Oct 13, 2015 4:25 pm    Post subject: Reply with quote

I don't own the 20 mm CZJ Flektogon but the quality seems to be OK. Generally old super-wides are not really comparable to modern optics.

Just for fun (a coating test but still...), here is my Flektogon 35/2.4 at Canon's cropped sensor.
CZJ Flektogon MC 35/2.4 at f/8.0

The borders are worse than Mir-1V 37/2.8 or S-M-C Takumar 35/3.5, let alone modern stuff like Tamron's zoom. I'd say these Flektogons are not really great at infinity.


PostPosted: Tue Oct 13, 2015 9:56 pm    Post subject: Reply with quote

I also have a 20/2.8 MC.

Here is an unscaled center crop at f/2.8:



And at f/8:



Is this much softness even in the center at f/2.8 normal? (I've read in some places that it should be sharp at least in the center even wide open.)


PostPosted: Tue Oct 13, 2015 11:32 pm    Post subject: Reply with quote

That's bad.
Any separation, haze?


PostPosted: Wed Oct 14, 2015 6:00 am    Post subject: Reply with quote

I just bought a 20/2.8 too in near perfect condition but sadly very similar performance as std's and glaebhoerl's. Sad I think this is not normal, but might be very common. As far as I can tell, the problem is the alignment of the rear lens block. In the factory it was probably a high precision operation to install the rear block but then as soon as one opens the lens (for cleaning, etc) and takes the rear block out, it will inevitably go back in slightly differently than originally installed. And a few microns could make a huge difference in image quality. I tried a few different alignments in my lens last night but couldn't get it right. But the characteristics of the glow and softness changed every time so I'm sure it is possible, I'm just not sure if one can do it with just trial and error and no special fancy equipment. Neutral


PostPosted: Thu Oct 15, 2015 7:47 pm    Post subject: Reply with quote

A little trial&error alignment of the rear block got me an almost good lens.

The lens as I got it was extremely bad at f/2.8:



After a bit of tinkering I got this:



After a little fine tuning on the front I think I'll have a very good lens. Smile


PostPosted: Fri Oct 16, 2015 10:20 am    Post subject: Reply with quote

Himself wrote:
That's bad.
Any separation, haze?


Nah, the glass looks flawless to my untrained eye.

miran wrote:
A little trial&error alignment of the rear block got me an almost good lens.

[...]

After a little fine tuning on the front I think I'll have a very good lens. :)


That's good to hear! I should probably try that as well, then, although I've never repaired a lens before.


PostPosted: Fri Oct 16, 2015 10:51 am    Post subject: Reply with quote

glaebhoerl wrote:
That's good to hear! I should probably try that as well, then, although I've never repaired a lens before.

I think it's a good lens to start, although perhaps something more expendible might be even better. But at least this seems to be (at least in my experience) one of the easier lenses to disassemble/reassemble. It's just that obviously it's very sensitive to minute changes in alignment of the lense elements, especially at the rear. And you definitely need proper tools, otherwise it will be very difficult and there's a good chance you'll make at least cosmetic damage to the lens or worse.

My advice is to first work on the rear to get it centered and then if needed also adjust the front. As far as I can see (I could be wrong) misalignment of the rear block affects sharpness in the center and smearing in the corners while the position of the front block changes the plane of focus and field curvature. Both need to be properly adjusted.

To get to the rear block you need to unscrew the three large screws at the back (don't touch the two smaller ones) and the mount and aperture mechanism (with all the tiny fidly bits) comes off as one separate unit, giving direct access to the rear lens block. Don't take the rear block apart, there should be no reason to. You can take the whole block out and put it back in carefully to make sure it's perfectly centered. It's held in place by a retaining ring and until it grabs, there's about half a milimeter of play - it moves laterally in its place a tiny little bit. It's extremey difficult to align it perfectly with the axis of the lens. And also maybe orientation might be important, I don't know. It took me many attempts before I found a position that worked.

To get to the front part of the lens, you first need to unscrew the nameplate ring (using a rubber tool or similar). Then the whole front lens block again comes out as one unit. No need to take that apart either unless it needs cleaning but it shouldn't because it's a tightly sealed unit. Unlike the rear block the front is just screwed in place with a stopper inside the threaded tube. Focal plane adjustments are made by how far down the thread you screw the lens block. Again it's a metter of trial and error to find the right position. I still have to do this on mine, I think, it's still not as it should be.

Good luck and let us know how you do. Smile


PostPosted: Sat Oct 17, 2015 1:28 am    Post subject: Reply with quote

What kind of tools? Apparently I don't even have an appropriate screwdriver (I have like 5, but they're all the wrong size or shape!), so I'll have to get one next week.

(By the way, mine has 6 large and 2 small screws at the back (it's an "electric MC" version), but I guess that just means I have to unscrew the 6 big ones instead of 3.)


PostPosted: Sat Oct 17, 2015 5:55 am    Post subject: Reply with quote

I have a set of tiny screwdrivers from Pro's Kit, a set of rubbers from Micro-tools and a lens spanner also from Micro-tools.


PostPosted: Sat Oct 17, 2015 7:00 pm    Post subject: Reply with quote

I also managed to get a little bit better image than before thanks to Miran and his instructions Smile
It is not perfect, but it's much better than before.
Friends cheers Miran