REPAIR Carl Zeiss Jena Flektogon 4/20mm

[stevemark]

OK - here we are. Removing the front namplate is usually the first step when servicing a Carl Zeiss Jena (CZJ) lens from the 1950s and 1960s. It often is also the most difficult since the front ring usually doesn't have any slits, and therefore a lens spanner wrench is useless; a rbber tool must be used. As soon as there is a slight damage to the outer front part itself, removing of the name plant becomes nearly impossible. Even if there's no damage, the front name plate often is "glued in" by dirt, traces of oil and fat, and dust or corrosion.

In my case the front ring seemed undamaged, but the ring nevertheless refused to go off. I had to soak it for a few minutes with some acetone, and then it cam loose:




Now the ring holding the front lens in its place may be revoved:



The front lens has some nicely sprawling fungus on its back sinde:



Ring removed:



Front lens removed - cleaning was easy, and no permanent damage could be seen:



The next (second) lens is slighhtly fogged, as it can be seen here. Cleaning also was easy:



After re-inserting the front lens and the corresponding ring I tried to remove the entire optical block from the housing by unscrewing this ring:



However the optical block only became wobbly and couldn't be removed, so I had to start opening the lens from the rear. If the screws don't come loose easily, apply some acetone first and wait for 1-2 minutes; that's usually quite helpful:



Rear part comes off nicely:



Looking at the remaining lens block - the silber (alu) aperture ring now simply can be lifted off:



ATTENTION - do not lose this small part (not a ball, but a small pin in this case) and the small metal acting as "spring" (not a spiral spring, but rather a small flat steel part acting as a spring):



Quite a bit of dirt and old grease:



Since the optical block in its entirety still doesn't come out (but still wobbles of course) I decide to remove the optical front group:



Once the front group has come off, we can see the typical Zeiss way of stamping and marking all the optical groups with a partial SN as well (usually the las three or four digits):

[stevemark]

Now let's separate the two parts of the focusing mechanism! First we need to remove the two corrsponding guides (i. e. the four screws holding them in place):



Guides are removed (beware, there are two of them):



Before actually separating (extracting) the inner part, be sure to set the lens to "infinity" as shown here. That's useful for clearly marking the exact spot where the two parts of the focusing mechanism are separating:



The inner and the outher part of the focusing mechanism - I just have marked the position where they came apart:



The outer part consists of two main parts as well. Before separating them we should measure it's thickness at the "infinity" position:



Before unscrewing the two parts we must remove this petty large screw ahich is acting as a "stopper" for the infinity and MFD positions of the focusing mechanism. It's slightly rusty, but it's strength isn't compromised at all:



In this case the two parts came apart just at the "infinity" position, and therefore an additioanl mark was unnecessary of course:



The entire lens block still is wobbling inside, but still canot be extracted! First we have to remove the transmission mechanism which connects the aperture ring and the aperture itself:




Second, the connection between the "Druckblende" (German term for the button mechanism on the lens which quickly closes and re-opens the aperture once you press it) and the aperture mechanism must be removed:



Before actually removing it, look carefully at how the connection is made - later on it will help once you have to re-assemble things ...



Transmission mechanism (including a spring!) removed:



Now, FINALLY, the entire lens block comes out!!



There's a distence ring involved as well:



Now we can extract the rear lens group (actually a cemented triplet) - there are four consecutive etal rings, all with slits; so be sure to turn and remove the right one (the second outermost):




The rear lens group, a cemented triplet as said above, is pretty dirty as well. I did not take out the actual cemented lens from its housing, but rather decided to clean it "in place", as this would remain its centering. Cleaning was a bit tricky - the lens is pretty small, and the fogging on on its front (=inner) surface was pretty strong. Apart from diluted detergents I also had to use a few Q-tips saturated with acetone. Be careful, as too much acetone might affect the cementing of this triplet!!




Well, finally we are done dismantling the CZJ Flektogon 4/21mm:



The front lens group is shown in the upper right corner (yellow arrow); apart from two fogged surfaces (one of them with fungus) just between first and second lens, all other surfaces were perfectly clean - which means I didn't have to take apart it completely.

The rear lens group (yellow arrow at the bottom) was cleaned as described above.
Finally the focusing "rubber" (plastic) ring (red arrow) which had become loose and very brittle was split in two halves. These two halves had to be treated very carefully (to avoid further decay), and they later on were re-glued using "Pattex Repair Extreme" glue, a highly elastic silane modified polymer which is perfectly suited for such problems.

[stevemark]

After cleaning thoroughly all the parts, re-assembling was fairly easy. The aperture mechanism itself was in a perfect shape - dry and snappy, and therefore I didn't touch it:




The entire lens block is re-installed and the transmission for the "Druckblende" (what's the correct English trem??) is in its correct place again:



Transmission mechanism from aperture ring to the apertre itself is built in again:



The focusing mechanism is re-assembled - the only thing missing is the rear of the lens barrel with the Exakta baynet mount:



The cleaned and restored lens on a nice late Exakta Varex VX1000 (labelled as "Elbaflex" for Export into the "NSW" = "Nicht-Sozialistischer Wirtschaftraum" = "free world"):


OK, finished

That was a nice and pretty easy maintainance (at least once the front ring nameplate had come off). The lens feels smooth again, the focusing ring doesn't slip any more, and - last but not least - the lens is resortored back to its original rather impressive contrast. Impressive contrast for an early 1960s superwide of course, and only if you use it at f11, but nevertheless ... !

I must say I'm positively surprised by this lens. Don't expect a "perfect lens" based on the Carl Zeiss Jena nameplate, it's a historical lens by all means, but expect a lens not just with "character" (often used for lenses with crazy weird rendering), but a lens with "good character" or "useful charcter": Techically quite good at f11 (low distortion, low CAs, low vignetting, good contrast & good detail resolution on 24 MP FF), but als resulting in nice "glow" and potentially useful vignetting at f4 o f5.6.

If you can get a less-than-perfect sample for little money (this one came for CHF 115.--) - get it an do work necessary to restore it; I've shown here how to do it

S

[Attila]

[stevemark]

Thread with technical information about the lens, as well as image samples before and after cleaning here:

https://forum.mflenses.com/carl-zeiss-jena-flektogon-4-20mm-t86338.html

S