Repairing LOMO APO 40x0.95 Microscope Objective
LOMO APO 40x0.95 objective is one of the best in it's class. Unfortunately, most of them are quite old (40-50 years), and share same problem - completely stuck cover glass correction collar.
But good news is that you can repair it! I'll show you how to do this. You'll need some simple things:
- watch screwdriver (1.4 mm or less);
- cotton sticks;
- dry solvent;
- ultrasonic bath is recommended but not necessary.
Let's fix my APO 40x0.95 made in 1968. I've tried to disassemble it without use of solvent first, but just scratched it with no success. So, it is better to apply solvent from the very beginning.
Apply solvent with a cotton stick to the places marked on the picture below. Be careful to not put solvent on the glass. I'm not sure how it will affect glass, so it is better to avoid risk.
After solvent gets into the holes, get your screwdriver and remove three stop screws that hold the scale ring in its place.
Unscrew the rear black ring then. It is quite easy to do with just your fingers.
Unscrew next black ring. This one is bit more tricky. It holds a spring, and you should push its grooves with the screwdriver counter-clockwise to unscrew the ring. Be careful to not let the spring fire the ring.
Solvent should be deep inside the objective by now, hopefully. Try to unscrew top cap counter-clockwise. If it doesn't move yet, apply bit more of solvent to the top holes to reach thread with solvent.
Further on, you should mark position of different parts relatively to the brass body. Select some sort of index for you (I've choose the stop screw hole in the beginning of the scale). Mark this position on the body with the screwdriver as pictured below.
Remove the scale ring and take note of the small part that limits rotation of the correction ring (so the index moves within the scale limits).
Take this part out and remember it's top position if it has a pin on it's side.
Mark position of the index mark now. AND take note of the gap size in the round holes. Top edge of the inner block is approximately in the center of these holes in my case.
Unscrew the correction ring now and see how much green old grease there. That is why the ring was stuck.
You should take the inner block out of the body now. Push the side threaded parts down. But it will be stuck too, most probably. So, you have to apply solvent again carefully. I've screwed out one more black ring from the rear to remove two small lenses out of the block and to apply solvent more safely. If you able to push inner block out without disassembling the inner block, it is better.
After you disassembled the objective, clean it with solvent. Apply cotton sticks or use you ultrasonic bath. Take note that the body and inner block have cross marks. These were made at factory.
Assembled inner block looks like shown below:
It is not necessary to disassemble this block, but I had to do this. If you want to clena it thoroughly, you should take the lenses out. Unscrew the black ring and take the elements off.
Take note that inner elements are different. When you will assemble the block, insert shorter element first.
After you cleaned all parts, it is time to assemble them back. First of all, assemble the inner block if you took it apart. Insert the inner block into the body. Make sure that you aligned cross marks on the block and the body. I didn't lubricate any parts since they were moving easily. But you may need to add some grease.
Insert the spring and secure it with the ring, screwing it clockwise. Check mechanical condition by pushing the side threaded parts down. If the spring returns the inner block to up position, it is fine. If not - you'll have to disassemble it again and to check what is wrong. May be you just need to lubricate it. Or may be there is some deformation, and you need to file metal a bit. But this is rare case. Hopefully, you objective works fine at this stage.
Screw the correction ring onto the body. Align index of the ring against the mark you made during disassembling, and check the gap in the round holes. Picture below shows wrong position - index is aligned, but gap is too small. It is necessary to turn the ring back one full turn.
Gap is correct now - it is same as it was when we saw it during disassembling. Put the limiter into its slot.
Put the scale ring onto the body and secure it with three stop screws.
Screw the top cap on, and you've done!