Repair despair - Trying to fix a CZJ Tessar 50

Sometimes, it might be better to give up on a repair and just hurl the whole lot in the bin.

I have just managed to get a Carl Zeiss Jena zebra Tessar 50mm back together after stripping the whole thing down to clean up the stuck aperture blades; apparently a common problem. On this lens, well on my copy at least, unscrewing the front element means that the aperture blades will come loose and fall out, meaning that the whole thing must be stripped so that the blades can be put back. No short cuts with this lens and it nearly went in the bin at that point. However, I persisted and got the aperture assembly back together. That job done, the aperture was again nice and "snappy".

Eventually, I managed to get the lens back together and focusing properly, although not particularly smoothly. The only problem is that now the blades are slow in stopping down. It can't be that they are oily, so I suspect that the remaining problem is a weak spring, combined with a poorly designed operating mechanism. Its a shame really, as the lens is in otherwise good condition. Right now, I could happily hit it with my 18lb long handled lens adjusting tool (othewise known as a sledge hammer).

Time to step away from it and put it on the shelf for later. Can someone please tell me that this lens is worth this much effort? No, I thought not....

Maybe the aperture blades have too much grip? Could a little bit of graphite help maybe?

I would hit it w/ the hammer. Those sort of things are a lot of fun. It will make you feel better, and then you can move on and buy another one. Make sure you wear some eye protector of some sort, or you may create other problems. You learned something about the construction of the lens, which will help you in the future. Afterwards, have a nice glass of red to celebrate, or your favorite relaxant of choice.

I would say shoot some shots with he aperture at whatever is sticks at and see if its worth it.

Cheers for the replies guys. I did take a quick test shot of the cat with the lens this morning (digi is good for something!) and it actually is a pretty good at F4, so I guess that it, the lens that is, will live to see another day. The cat, however, did look a bit rough, so all bets are off for him

Anfenglin: Thanks for the suggestion. I have read elsewhere that the springs in these lenses can age and weaken, so I think this is the most likely problem. It does stop down, albeit slowly, so I think I will just leave out the auto aperture mechanism and try using it in stop down mode.

While I have been using extra fine powdered graphite on large format shutter and aperture blades I recently came across a vintage lens that did not like the graphite, it actually worked worse with it. I flushed it of the graphite and used dry Teflon, http://www.amazon.com/DuPont-Non-Stick-Dry-Film-Lubricant-Squeeze/dp/B00BCVXUR6/ref=pd_ybh_2 and now it works smooth as silk.
Try some, it may help that older spring do its job.

Is the actuating ring also clean? It very likely needs to be with one of those lenses, for the blades to have a shot at moving rapidly enough.

A quick follow up: The lens is now stopping down cleanly after a second strip and clean. Obviously, my first effort wasn't good enough and it seems that the aperture mechanisms on these lenses must be spotlessly clean in order to function at all. No wonder that so many of them have aperture problems

Thanks to everyone for the advice