Markus Wobisch: Repairing a Nikon Series E 50mm f/1.8 Lens

The Nikon Series E 50mm f/1.8 lens was a cheap version of Nikon's Nikkor 50mm f/1.8 AI lens, built to accompany the cheap Nikon EM camera. It has exactly the same optics, but only single-coated, and housed partially in plastic. It was built from 1979-81 in a "black version" and from 1981-1985 with a silver ring - this is the version that we are looking at.
In the piece that I am holding here, after 40 years, the optics are still fine, and so is the aperture. Only the lube has dried and the focusing feels awful. So, no work is required on the "optics plus aperture" piece - only on the focusing helicoids.

Tools

This is what is needed for the job.

JIS (Japanese Industrial Standard) screwdrivers since the screws in these Japanese lenses are not Phillips screws, but JIS screw heads which are slightly different. Using a Phillips screwdriver can easily ruin the heads. So do yourself a favor a buy a set of Vessel screwdrivers. I got a set for $13 and the quality is much better than any other (cheap) screwdriver set I ever used.
High percentage Iospropyl Alcohol (I got 91%) and cotton swabs (for cleaning all surfaces and the old grease in the helicoids)
Helicoid grease

Disassembly

I strongly recommend to take photos of every single step along the way. Whenever I take off a piece of the lends, I clean immediately all accessible surfaces with alcohol-soaked cotton swabs.

First, I remove the three screws from the bayonet mount plate. I had a hard time getting these out. I soaked the heads in alcohol and heated the last one with the tip of a soldering iron to get it out.

When removing the bayonet mount plate, notice the long pin and the slot from which it came.

Then, the aperture ring can be removed. Notice, how the U-shaped piece came was holding a pin on the lens.
For the following steps it is important to set the focus to a well-defined value (I pick infinity) and make sure it stays there. Otherwise it may be impossible to put the lens back together again without many trials and errors.

Then the two helicoid keys (which ensure that the barrel moves forward and backward while focusing but does not rotate) can be removed (some of these screws were also hard to get out). Try to remember which one was on the left and which one was on the right, so you can put the back at the correct position. Be careful not to rotate the inner part. First, take a few pictures to remember how it looked like, so this can be reproduced later during reassembly.

This is, how the pieces align at infinity focus.

Then, from the front, I look at the inner helicoid (with the optical piece). I notice that it can be turned clockwise only by a small amount (maybe 5 degrees) before it gets stuck.

From the original (=infinity) position it can be rotated (very carefully!) by a little more than half a turn counterclockwise - then it comes out (that's where I took this picture). The red arrow shows the path from where the left slit starts (as in the pictures above), before the helicoid comes out when it is on the right side. I used the structures indicated by the yellow arrows to remember the exact position where the helicoid comes out. Unlike typical screws, the helicoid has many entry points and it is important to remember the correct one - otherwise the lens will later not be able to focus to infinity.

Another picture to remember the position where the helicoid comes out. This is the point where one clearly sees why this E-Series lens was a budget product: The inner element with the optics is only made of plastic - really sad!

Now that it's out, one can see the dirty old grease on both sides.

After removing the three screws, ...

... the focus ring can be removed. (I placed it such that infinity is pointing to the top.)

Now, the silver ring can be removed after loosening the three screws. But be careful, not to rotate the inner ring while doing so.

Then the helicoid can be removed. Before I unscrew it, I checked that it can be screwed (counterclockwise) by a little more than half a turn into the black piece before it gets stuck. Then, from the original position, I turn it clockwise and after six full turns, plus approx. 20 degrees, it comes off.

This is as far as the disassembly goes - these are all the pieces (except for the screws and the helicoid keys - these are safely stored). Now everything gets cleaned - in particular the helicoids.

Reassembly

First, I put back the silver ring, making sure the position of the silver pin matches the corresponding space (red arrow), by putting back the three screws.

I put a tiny amount of helicoid grease (with a toothpick) at three spots on the inner side of the black piece. Using more will make the focusing very hard.

I insert the helicoid so it sits exactly as it did before (and I check that it can still rotate a little more than half a turn before it gets stuck - to be sure it sits exactly as it did before). I rotate it a few times four turns out and in to ensure that the grease is evenly distributed. (Before I do that, I did it a few times without grease, just to ensure that I can get it right).

Then I add the focus ring with its three black screws.

I put small amounts of helicoid grease at three places on the inner part and insert the optical piece with the helicoid exactly as it came out (again: before I do that, I did it a few times without grease, just to ensure that I can get it right).