I found a good Youtube tutorial on tearing down the Jupiter-12 LTM focus mount. I've been fortunate in that ones I've come across have not needed the old grease taken out and new put in. Until now...
First: A really good Video:
Next, my pictures and some notes from following it.
First: "most" but not all, Shims from the Jupiter-8 work with the J-12.
Second: Most J-12's Benefit from shimming custom for the Leica standard if that's what you plan using it on.
Third- Like many ex-Soviet lenses, a lot of deviation from sample to sample. The one worked on today: the focus mount could not drive the RF to infinity, and the Shim was way off. Plus side- the lens, made in 1958, looked like new. No one used it.
Step one: unscrew the rear group.
Step Two: Unscrew the front group, keep shims with the lens. I use a rubber cork.
Step Three: Take the three set screws out of the focus ring. I keep the screws in order, to put back in the same holes. Experience.
Step Four. remove the Helical From the Mount. Make a Scrive Mark for the Infinity Mark, and for the position of the Set Screw.
Step 6, Turn the Two Guide Screws for the innermost Helical so they are perpendicular to the slot and with the lens set to Infinity make Scribe Marks for their position. It is about 1/2 way. This is different from the J-3. There are MANY starting locations to rethread the helical. The scribes are required to get the thing back together.
Infinity,
After making the marks, take out the two guide screws. I keep them in order of the slots they came from. Then remove the inner helical.
Step 7, much like the J-3. Remove the Stop screw for the close/infinity slot. Screw the Helical inward as far as it will go, which should not be too far. Note this position, if you decide to separate the helical, this will indicate that you have the correct position. There are MANY possible starting positions, and only one correct one.
Remove the screw, separate the helical. I used 91% Isopropyl alcohol to clean. I also had to use a lot of Q-Tips and even scrape old grease off with a fine screwdriver.
Yuch. Yak Ear Wax.
Remember all those scribe marks? I did...
This lens looked like new. It did not drive the RF cam to infinity, and focus was WAY off. I used a "quick-fix" for the RF cam, put one layer of Copper tape to drive the RF to infinity. This cam rotates as you focus, to the extra thickness cuts out at 2m. I shimmed the lens to be accurate at 5m on my M8. It just works.
First: A really good Video:
Next, my pictures and some notes from following it.
First: "most" but not all, Shims from the Jupiter-8 work with the J-12.
Second: Most J-12's Benefit from shimming custom for the Leica standard if that's what you plan using it on.
Third- Like many ex-Soviet lenses, a lot of deviation from sample to sample. The one worked on today: the focus mount could not drive the RF to infinity, and the Shim was way off. Plus side- the lens, made in 1958, looked like new. No one used it.
Step one: unscrew the rear group.
Step Two: Unscrew the front group, keep shims with the lens. I use a rubber cork.
Step Three: Take the three set screws out of the focus ring. I keep the screws in order, to put back in the same holes. Experience.
Step Four. remove the Helical From the Mount. Make a Scrive Mark for the Infinity Mark, and for the position of the Set Screw.
Step 6, Turn the Two Guide Screws for the innermost Helical so they are perpendicular to the slot and with the lens set to Infinity make Scribe Marks for their position. It is about 1/2 way. This is different from the J-3. There are MANY starting locations to rethread the helical. The scribes are required to get the thing back together.
Infinity,
After making the marks, take out the two guide screws. I keep them in order of the slots they came from. Then remove the inner helical.
Step 7, much like the J-3. Remove the Stop screw for the close/infinity slot. Screw the Helical inward as far as it will go, which should not be too far. Note this position, if you decide to separate the helical, this will indicate that you have the correct position. There are MANY possible starting positions, and only one correct one.
Remove the screw, separate the helical. I used 91% Isopropyl alcohol to clean. I also had to use a lot of Q-Tips and even scrape old grease off with a fine screwdriver.
Yuch. Yak Ear Wax.
Remember all those scribe marks? I did...
This lens looked like new. It did not drive the RF cam to infinity, and focus was WAY off. I used a "quick-fix" for the RF cam, put one layer of Copper tape to drive the RF to infinity. This cam rotates as you focus, to the extra thickness cuts out at 2m. I shimmed the lens to be accurate at 5m on my M8. It just works.
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