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11-10-2015, 12:13 PM - 2 Likes   #1
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Carl Zeiss Jena Flektogon 35mm f/2.8 FULL DISASSEMBLY + BONUS COMPLAINTS

Carl Zeiss Jena Flektogon 35mm f/2.8 m42 mount COMPLETE TEARDOWN

OK, so I recently did a CLA/Repair for another PF member on a sample of this lens that was having some problems with the preset aperture mechanism. I present this teardown to you as both a useful tool and a warning. This lens, though relatively simple in design, was one of the BIGGEST pains in the $#@ to disassemble and reassemble I’ve ever encountered.

People who know me well on this forum know that I like to complain about some of the puzzling decisions made in German lens designs as compared to their much more elegant and sensible Japanese counterparts. This lens is a prime (pun intended example) of this phenomenon in work. I get what the designers were trying to accomplish – no visible set screws on the exterior of the lens. But what we are left with is a nightmare for any lens tech trying to repair one of these. The problem is, they took what is a very simple lens design and made it extremely difficult to disassemble and reassemble. If pressed, I can take a similar-vintage Takumar down to individual parts in about 10 minutes. Let's just say this one took somewhat longer and leave it at that.


So, without further ado, the teardown.

RECOMMENDED TOOLS:
- Good slotted head screwdriver set with regular and micro sizes
- Rubber tool (I use a size 9 bung stopper, available at most homebrew stores)
- Lens spanners - it would probably be useful to have both slotted and needle point types
- needle nose or jeweler's pliers
- Solvent - I prefer Methyl Ethyl Ketone (MEK)
- Patience

1.From the front of the lens, remove the trim ring with a rubber tool by turning counter- clockwise. This lens had obviously been worked on before, as can be seen from the drilled spanner holes, which are NOT standard. A lot of the parts in this lens are glued, so if you are having trouble removing this piece, I’d advise applying a solvent like MEK before resorting to such drastic measures as drilling/



2. Beneath the trim ring, you will see a series of rings with spanner notches. Applying rotation to the outermost ring will allow the entire front optical group to be removed. This can be broken down completely by removing the inner spanner ring on the front of the group, the second ring deeper in the group, and the retaining ring on the back of the group.





3. Flip the lens over. You will see multiple retaining rings. The outermost one can be removed with a lens spanner, allowing the entire rear group to pop out. the rear group is held together by a combination of glue and retaining rings, and is pretty self-explanatory to break down.







4. Now for the first tough part. The front and rear halves of this lens are able to be pulled apart in a very similar to those of the the Helios 44 m42 designs. However, instead of simply screwing together, as on the Helios, the halves of this lens are held together by a notched spanner ring. Unfortunately, it is REALLY Recessed deep down in the rear of the lens, and the projecting permanent baffle in the rear makes it impossible to remove using standard lens spanners. It’s also glued. To get it out took me a loooong time and a lot of work with some solvent and a couple of precision screwdrivers (one of which I managed to break), but eventually, I finally got it out. The really crappy part is that it’s even harder to get back in when you are done. I imagine that Zeiss used a specially designed spanner for this part which makes it a lot easier, but unless you live in Jena and happen across one at the local swap meet, I think elbow grease is the word of the day.



5. Once you’ve removed the ring, the two halves just slide apart.




6. Take a look into the rear half of the lens. See that slotted screw in there? That bumps against the infinity stop and keeps the helical from going off the end of its thread. Remove the screw.





7. At this point, you can turn the focus ring toward the shorter focal range, past where it normally stops. Once the front half of the helical has cleared the synchronizing rails, (it will start to rotate with the focus ring), stop turning the focus ring and instead turn the front half itself until it exits the thread and comes off the front. Carefully etch a mark at matching point on the corresponding halves so you know where to rethread it later. This lens does NOT have easily adjustable infinity focus, so if you thread it at the wrong place, you are screwed.



8. Now you can lift out that spanner ring you had all that trouble removing in step 4 and similarly unscrew the rear half of the helical. This one has only one thread entry point, but you will want to carefully count and write down the number of revolutions it takes to remove it. (Side note/complaint – if you turn over and look at the front side of this part, you will see both the infinity stop and the helical synchronizing guides. Unlike on most lenses, these guides are permanently attached to the helical, meaning if your infinity focus is off, you have to disassemble the lens all the way back to this point and try blindly until you happen upon the right combination of positions. NOT FUN.)





9. That’s it for the disassembly of the rear section. Now let’s move on to the front. If you look at the side of the barrel, you will see a screw stop keeping the lower preset aperture ring from moving past a certain position. Remove the screw.




10. There is also a spanner ring that holds both aperture rings on. This one is also a pain to get off, due to the stop shown on the right which blocks one of the spanner notches as you turn. I had to come in from an angle to get this ring out.



11. Once you have gotten the spanner ring off, carefully lift out the aperture stop/positioning ring.



12. Next, lift out the lower aperture ring. Be careful not to lose any of the four springs! They drop out easily.



13. Now you can see another slotted screw. This connects to the aperture guide inside the lens and also holds the top aperture ring in place. Remove the screw, and the aperture ring will now separate from the front.







14. Now we get into the disassembly of the aperture.
aside - I highly recommend against disassembling the aperture unless you need to clean the helical, as I was doing here. The blades (all 12 of them) are a major pain to get back in place. If you do need to re-assemble the aperture at any point, then the easiest way I’ve found to get it back together is to coat the blades in grease before reassembling so they stick in place. When you are done, clean thoroughly with Naptha/lighter fluid to remove the grease once reassembled.
Flip the barrel over so you see the front. There is an internal circlip that holds the aperture guide tube in place. Use a needle nose pliers to squeeze the ends together and lift it out.






15. Now, the guide tube can be lifted out. As you can see here, on mine the aperture blades are already coming loose. Lift the tube out and the blades will fall right out.
Note for reassembly - when you put the guide tube in, and replace the screw connecting it to the aperture ring, the aperture blades should be advanced by one peg position from fully open when the screw stop is at max open. If you have them both at wide open, the blades do not close all the way.






Congratulations! Presuming you disassembled the lens cells, then the lens should be reduced to individual parts. If you are doing a CLA, you can clean all parts except for aperture blades with mild dish soap or another cleaner of your choice, and the exterior can be polished using a standard polish for soft metals. .An old toothbrush works particularly well to clean out helical threads. Make sure everything is dry before reassembly.
And oh, about that reassembly – it’s even more difficult than the disassembly. Make sure you don’t have any other plans that day!


Last edited by dcshooter; 11-10-2015 at 02:20 PM.
11-10-2015, 12:57 PM   #2
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That is a lot of work.
11-10-2015, 01:16 PM   #3
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Hey -- that's my lens!!!

Sorry, Brian. That's 3 lenses I've sent you that ended up a bigger challenge than expected. 2x - German and 1x Russian.

BTW -- fabulous work!! The Flektogon came back like new and is buttery smooth in operation!!
11-10-2015, 01:23 PM   #4
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QuoteOriginally posted by ripper2860 Quote
Hey -- that's my lens!!!

Sorry, Brian. That's 3 lenses I've sent you that ended up a bigger challenge than expected. 2x - German and 1x Russian.

BTW -- fabulous work!! The Flektogon came back like new and is buttery smooth in operation!!
Well... lucky for you I recently sent him some nice FA* lenses for CLA that probably were much simpler and made him smile and not curse the Pentax Forums name aloud repeatedly... LOL.

11-10-2015, 01:23 PM   #5
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Ah, very interesting, and nice photos.
Do you think the black f2.4 version (with 6 aperture blades) is similarly difficult to disassemble? (think the review here is about this version) Apparently there are a couple different Flektogon 35mm lenses
11-10-2015, 01:29 PM   #6
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I imagine it will probably easier, since it's an auto aperture design rather than a preset and appears, at least from the exterior, to be more modern in construction (they can hide screws under the grip). I have seen some craziness even in newer East German lenses, though, so no guarantees!

QuoteOriginally posted by Na Horuk Quote
Ah, very interesting, and nice photos.
Do you think the black f2.4 version (with 6 aperture blades) is similarly difficult to disassemble? (think the review here is about this version) Apparently there are a couple different Flektogon 35mm lenses


---------- Post added 11-10-15 at 01:48 PM ----------

Ha, the FA lenses have challenges of their own (those data forks are SOOOOO fragile), but yeah, European lenses in general tend to generate a lot more hair pulling than do Japanese-made ones. It's across the board, too. East Germany,West Germany,Soviet Union/Russia, Switzerland, and France all have provided me lenses with some puzzling/needlessly complex aspects. German ones do tend to be the worst, though. Just be happy that the Rollei QBM lenses are basically unadaptable to Pentax, since they tend to explode into a million tiny pieces as soon as you take the mount off. And I'm convinced that Schneider lenses are put together by Santa's magic elves when they are not moonlighting as brain surgeons.

QuoteOriginally posted by UncleVanya Quote
Well... lucky for you I recently sent him some nice FA* lenses for CLA that probably were much simpler and made him smile and not curse the Pentax Forums name aloud repeatedly... LOL.
11-10-2015, 02:22 PM   #7
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QuoteOriginally posted by dcshooter Quote
[SIZE=3]RECOMMENDED TOOLS:
- Good slotted head screwdriver set with regular and micro sizes
- Rubber tool (I use a size 9 bung stopper, available at most homebrew stores)
- Lens spanners - it would probably be useful to have both slotted and needle point types
- needle nose or jeweler's pliers
- Solvent - I prefer Methyl Ethyl Ketone (MEK)
- Patience
I think you missed the bottle of Single Malt Scotch!

M
11-10-2015, 02:25 PM   #8
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Ha, I actually thought about adding a step about enjoying your favorite adult beverage or anti-anxiety medication, but I figured it went without saying.

QuoteOriginally posted by MJSfoto1956 Quote
I think you missed the bottle of Single Malt Scotch!

M


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