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Ian
Rating: N/A
Votes: 0 (Vote!) | | Posted on Saturday, February 18, 2006 - 05:43 pm: | 
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This venerable old lens became stiffer until a vigorous attempt to "loosen" it ended in a totally non functioning focus ring. It is jammed at the near focussing end. Removal of the rear of the les allowed some oil to be applied near the focussing grooves, but no release. Is there anything else that I can do? |
Alex
Rating: N/A
Votes: 0 (Vote!) | | Posted on Thursday, February 23, 2006 - 04:07 pm: |
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You really don't want to put oil anywhere inside your Tessar, it will get on to the blades, however careful you are, and they'll stick. The blades have to be bone dry.
If you take the rear of the lens off, and make sure you take a note (or a digital photo) of where the bits and pieces are, like the pin which activates the diaphragm, you will find you can unscrew the front part of the lens right off. As I remember, it's a reverse thread. Take REALLY good note of the position at which it pops off, the threads are multistart, and if memory serves, there's about a dozen and a half re-entry points! It's a tedious job if you have to test each one individually on re-assembly. When you separate the two halves, look inside and you'll see a rail fixed to the rearmost half with two screws, and the front half slides up and down this rail during focussing. It's one of those things that are hard to describe, but very easy to understand when you see. I took this rail off to let me get better access inside the lens housing, and once again, make sure you take a note of the orientation, and watch out for the small spring that controls the aperture blades, and watch out when you take the aperture ring off, there's a tiny ball bearing inside which provides the click stops, try not to lose it! I work using an inverted box top lined with fabric, so that falling bearings don't bounce or roll off.
What I did was to take all the old grease off from every threaded surface, first with a rag, then some cotton buds (called Q-tips elsewhere), and then cleaned right in the grooves with cocktail sticks, to get all the old grease out. Finally I used alcohol on cotton-buds to get the threads as shiny clean as I could. Note that there will probably be old grease sludge which has migrated well beyond the threads, so get that too.
Regrease them using silicone grease - I got a tube from an electronics shop, and it will last you forever. I put spots of the grease at regular intervals around in threads, using a wooden cocktail stick to dot the spots on, put the lens parts together temporarily and 'worked' the threads to make sure the grease got distributed nicely throughout. I didn't want to put too much on, and the few spots I used are still working fine nearly a year later. Check you haven't had any of the oil migrate to the blades. My first Tessar was a supposedly 'excellent' condition specimen from Ebay, but that proved to be Ebayspeak for 'focus jammed', with the aperture also stuck at f/2.8. After re-greasing the threads, I'd to clean the stuck blades with napth (lighter fuel) in order to free them up and get them clean and dry. Timeconsuming, but just requires methodical working and patience. (Incidentally, I'd trouble with this specimen and eventually had to resort to using fine graphite dust applied to the blades using an artist's brush soaked in naptha.)
That done, you begin the re-assembly proper, this time using your notes of the orientations. This can be tedious, but it's not difficult, just time-consuming.
The CZJ Tessar is not a difficult lens to work on, in fact, it's quite satisfying, and if you've not opened a lens before, it's good experience. Once you've done it once, you'll be able to do your next in about a third of the time. (Well, that's how it was for me.) The result was a lens focussing beautifully smoothly, and a level of smug self-satisfaction that is frankly obscene. |
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