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Micro-Nikkor 55mm f/2.8 Aperture Blade Cleaning

I enjoy photography, and I love to tinker. I'm a died in the wool engineer, so I love to take things apart and see how they work. I'm also frugal (some would say cheap). Because of this, I've taken an interest in mounting old, high-quality, inexpensive manual lenses on my new digital SLR camera body. I've already gotten two Pentax Super-Takumars made in the late 1960's -- one from eBay, and one from a pawn shop. I'm always on the lookout at garage sales, estate sales, and pawn shops for more good deals on old glass.

I recently ran across a garage sale selling a Nikon FE body (made 1978-84) with a Micro-Nikkor 55mm f/2.8 macro lens attached. This is a highly regarded lens which will reach 1:2 natively and 1:1 with a 27.5mm extension tube. It's purported to be quite sharp through its entire range. Everybody loves it, except that this design has a chronic problem: oil leaks onto the aperture blades, causing them to stick. The lens I bought had already succumbed to this. I was too ignorant at the time to realize this and try to talk the seller down, but I still only paid $75 for a body/lens that, in working condition, could fetch $175 on eBay.

Since this was a common problem, I was surprised that there were no detailed instructions available on dismantling this lens, so here you go. Rick Oleson and Seymore from the ManualFocus.org forum were extremely helpful in directing me through this. It took me nearly two hours the first time through. By the third time I had to do it, it only took me 30 minutes.

Tools required:

  • Tiny Phillips screwdriver
  • Really tiny flat-head screwdriver
  • Tweezers
  • Q-tips
  • Isopropyl (rubbing) alcohol

Repair procedure:

  1. Note: Be careful not to smudge any of the lenses -- especially the interior ones -- during this process. Use clean hands and tools, and try not to touch any of the glass.
  2. Sit the lens on its nose, mount facing up.
  3. Remove the three visible screws on the lens mount.
  4. Pull the lens mount up and off the rest of the assembly. Set aside the mount.
  5. Remove the three screws from the thick tabs along the outer edge.
  6. Slide the outer body up and off the lens assembly. The aperture lever fits into a slotted track on the body. This track is spring loaded, and can be pushed outward to provide clearance for the lever to come out. Set aside the outer body.
  7. Remove the three rounded screws from the aperture mechanism.
  8. Lift the aperture mechanism off the main lens assembly and set aside the lens assembly.
  9. Remove the spring from the bottom of the aperture mechanism. This is where the really tiny flat-head screwdriver comes in handy. Set aside the spring.
  10. Remove the two flat Phillips screws from the top of the aperture mechanism. Do this while it's sitting on a table, so that the aperture blades don't fall out. Lift off the top half of the mechanism. Clean off any oil you see using Q-tips and alcohol, then set it aside.
  11. Lift off the blade cover plate with the lever and the dog-leg slots in it. Clean off any oil you see using Q-tips and alcohol, then set it aside.
  12. Remove the blades from the lower enclosure by flipping it over and using a pin or tiny screwdriver to push the brass hinge pins out of their holes. Be very careful not to bend the blades as you handle them.
  13. Clean any oil off the lower enclosure using Q-tips and alcohol. Make sure you clean inside the hinge pin holes.
  14. Clean any oil off the aperture blades using Q-tips and alcohol. Use tweezers to handle the blades, and be very careful not to bend any of them. Make sure you clean the hinge pins, too.
  15. Replace the aperture blades inside the lower enclosure. The blades lie so that their tips hook clockwise. The clockwise blade must lie beneath the counter-clockwise blade, so that the CCW blade doesn't hit against the CW blade's hinge pin when you try to open up the aperture. I made that mistake the first time. Make sure that you tuck the final (seventh) blade back underneath the first one.
  16. Now, we reverse the disassembly procedure.
  17. Install the blade cover plate with the lever and slots. The brass guide pins on each blade should fit into the slots. Make sure that the blades open and close correctly when you rotate the plate using the lever.
  18. Install the top of the aperture mechanism using the two flat-top screws. There's some wiggle room in the top piece's screw holes. If you can see where the screw heads lined up before, line them up with those marks again. This wiggle room will slightly affect how far the aperture blades open at a given setting.
  19. Install the spring on the bottom of the aperture mechanism. One end of the spring seemed slightly larger than the other, and I put that end around the brass pin. The smaller hook was put around the tab that protrudes from the bottom of the blade cover plate. If you did a good job cleaning, the spring should quickly and easily return the blades to their minimum aperture when at rest. Moving the side lever should open the blades all the way.
  20. Install the aperture mechanism onto the lens assembly using the three rounded screws.
  21. Slide the lens assembly into the outer body. There is a tab on a brass ring near the bottom (front) of the lens assembly that must fit into a groove inside the body's barrel. Press the spring-loaded aperture ring bracket outward in order to slip the lever from the aperture mechanism into the slot. This part gave me lots of trouble until I realized that the slotted bracket was spring loaded.
  22. Secure the outer body using the three screws in the thick mounting tabs.
  23. Move the aperture ring on the body while watching the blades. Verify that they make a perfectly round circle when opened to f/2.8. If not, you can loosen the five inner screws on the aperture mechanism (steps 18 and 20) and then use a larger screwdriver or something to rotate the bottom of the aperture mechanism relative to the top of the mechanism.
  24. Install the lens mount and secure it with the remaining three screws.

I want to apologize right now for the lousy lighting in these pictures. I've learned so much since they were taken... really.

This article was rewritten -- with color corrected photos -- on the Prairie Rim Images blog.

 

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Originally written 20 Jun 2008
Obi-Wan (obiwan@jedi.com)




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