Miranda 50mm f/1.9 focus thread clean up.

Last week I took ownership of a Miranda Automex III 35mm film camera and found that the helicoid was in need of re-greasing. I have already rebuilt the aperture on one of these lenses and found them easier than most to work on, so I thought it would probably not be too hard to re-grease the helicoid as well. The following is a pictorial guide for anyone who may find this useful.

The tools you will need are:

  • Watchmakers screwdrivers
  • Tweezers
  • Wipes, paper towels, cotton buds etc
  • Lithium based grease
  • Lens spanner

The basic strip down process is the same as the previous post for cleaning the aperture blades, but you need to take another step to get to the helicoid. To make it easier, here is the complete process I used.

  1. Remove the name plate from the front of the lens by unscrewing it anticlockwise.
  2. Unscrew the front element from the lens with a lens spanner.
  3. If the aperture blades need cleaning this can be done now, or the aperture can be left as a unit to be cleaned later or left alone.
  4. Now unscrew the 3 small screws in the focus adjustment ring. Once they are unscrewed you should be able to turn the ring independently of the inner mechanism and it should turn and slide off the front of the lens.
  5. You can now grip the front of the helicoid and twist it out of the lens.
  6. Next remove the 3 small screws in the ring with the depth of field scale on. Once these are out the bottom part of the lens will come off.
  7. Set aside the lens mount assembly, and unscrew the part you have just removed from it. Once it is apart you need to clean all the old grease from all the threads. I found a good way of doing this is to use a cotton bud soaked in some of the new lithium based grease you are going to use to re-grease the lens with. This really gets into the threads and cleans it out.
  8. Once all the threads have been thoroughly cleaned apply a thin coat to all the threads and start by threading the brass ring on to the black plastic depth of field scale. You thread them together until they are almost fully engaged.
  9. Once those two components are assembled together you can screw the re-greased helicoid back into the front of the brass ring. Screw it as far as it will go so that the back of the helicoid projects out of the back of the lens.
  10. Now you re-assemble the lens mount onto the back of the lens. You will see there is a slot in the helicoid and a spigot in the lens mount. These need to line up and when they do the lever which adjusts the aperture will also mate with the arm in the lens mount that controls it.
  11. Once the two pieces are together you have to carefully rotate the pieces until the screw holes in the two parts meet up and refit the screws (you need to make sure the helicoid is still well back in the lens, otherwise when you adjust the focus the helicoid will unscrew from the front of the lens)
  12. When the screws are in place, refit the focus adjustment ring over the front of the lens. There is a spigot on the ring and a slot in the brass ring it fits over so align these and it should be easy. Push the adjust ring over and turn it until the infinity mark lines up. Screw up the 3 retaining screws.
  13. Refit the front element and the name plate.

Eagle eyed readers will notice that this lens is not in fact from an Automex III. That is because I did the procedure with my Automex lens and then repeated it to take pictures using another Miranda 50mm f/1.9 lens which I’ve had laying around for a while waiting for a helicoid re-greasing. Even more eagle eyed readers will notice that in my haste to take the photos for this post I actually re-assembled the bottom of the lens out of alignment with the aperture scale! If you follow these steps, make sure you get them lined up.

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