Hel(icoids) and back: regreasing a Nikkor 28mm f/2.8 AI-S

Maintaining older Nikkor lenses has become easier with resources such as Richard Haw's website and also Kenneth Olsen's YouTube channel. However servicing details for my Nikkor 28mm f/2.8 AI-S at this point are still not as widespread as some other lenses and with a lens thats approaching 40 years old, its in need of helicoid servicing as observed by a dry and gritty focus tactile feedback.

Unfortunately, even with the previously mentioend resources above (I don't believe there exists a specific YouTube tutorial), there were some admenents that would help those new to the 28mm. Here's my notes for seperating the helicoids of my Nikkor 28mm f/2.8 AI-S in order to regrease.

This is not a trivial lens repair - only attempt if you are confident of your experience and skillset. A number of steps are skipped assuming you are already familiar with basic maintanence of this particular lens

This post is a personal supplement to Richard Haw's 28mm repair guide.

Tools

I'm using a set of Vessel TD-56S drivers including a JIS 0, JIS 00 and 1.2mm slot drivers along with tweazers, a dentist tool, and a rubber strip. I'm using the lighter resistance Japan Hobby Tool #10 grease since there are 3 helicoids that turn when focusing. Kenneth Olsen had a video comparing JHT #10 vs JHT #30 vs Helimax XP with thoughts on differences and application.

Marking the original positions

Mark the positions of the 2x helicoid keys and CRC tab when the lens is at the infinity and MDF positions to gauge correct reassembly. Once marked you can remove the helicoid keys.




Finally mark the infinity position on the black paint to the rear of the chrome index ring.

DANGER: seperating the chrome index ring peice from outer helicoid

First step is the soften any lacquer on the helicoid key screws - removing the keys will NOT affect the lens' ability to hit the infinity and MFD positions; remove the 3x screws from the chrome index ring and finally remove keys.



Turn the rear clockwise as if you are turning passed MFD until you can reattach the chrome index ring; whilst this is not strictly necessary it helped me keep clear track - the chrome index ring provides the hard stop.

Have the focus ring infinity symbol facing you: you can hold the lens or have it sat front element down on the table as you slowly turn the chrome index ring whilst gently pulling up - do NOT turn the front section of the lens. The helicoid is free after about 5 clockwise revolutions and on my copy seperates with the index tab screw to right of infinity aligned with infinity.

Be very careful and MARK BOTH the black paint of the chrome index ring peice and the helicoid as they line up against the infinity symbol on the focusing ring. Use a permanent marker initial and then scratch this into the paint - this way you don't slip whilst trying to engrave your mark risking that you inadvertantyl lose positions. Mark the chrome index ring first - this peice is free floating whereas the outer helicoid is attached the the focus ring.


^{TWO separating marks aligned to focus ring's infinity symbol, on the lip of the helicoid and the edge of the black paint of the chrome index ring peice}

Note at this point, everything has been done at the rear of the lens. Inspect how the lens helicoids look when collapsed and at infinity.




^{helicoid measurements, rear optical block to front of focus ring when focused at infinity}

DANGER: seperating the outer helicoid from inner/central helicoid

With the lens at infinity (to keep the helicoid from dettaching) temporarily free the front retaining ring to access the focus ring screws. This is where we will separate the two main helicoids and exposing the central inner helicoid that is likely to be where 40years of grit and grime and settled.

Once the focus ring screws are loosened you have to VERY careful not to over rotate otherwise the helicoid WILL separate before you are ready to set the marks.

Reattach the front retaining ring by holding onto the rear element group's post - you will want to sit the lens facing down on a table to have control when seperating the helicoid and to avoid worrying about the focus ring dropping passed the rear element which will also likely cause seperate the helicoid at the same time.



You should support the lens and helicoids like below to avoid inadvertently moving anything - its still focused at infinity.



With the lens sat face down you can turn the rear element to get the lens at MFD and moving the outer helicod to the edge of the inner helicoid - now hold the outer helicoid, slowly unscrew the outer helicoid with constant but light pressure pulling up to know where it separates. Count the revolutions based on the mark on the outer helicoid lip to get a rough idea to reattaching but its not absolutely necessary. When the helicoid separates, locate the previous mark on the outer helicoid and place a mark on the flat surface of the inner helicoid. I will use the previous mark I made on the lens indicating the first separation position as my point of reference (remember it used to be aligned with the focus ring inifity symbol when attached). On this lens this helicoid separates at a position opposite the aperture post.


<sup>separating marks, with new mark made on the flat surface of the inner helicoid aligned to the outer helicoid's own mark



outer helicoid removed, inner helicoid marked with mating position</sup>

Lift the focus ring from the rear so it frees the lens over the rear elements.

Cleaning and Reassembly

I did not attempt to separate or regrease the CRC helicoid sine it sits mostly isolated from the outer helicoid that can be affected by dust and dirt ingress.

At this point you should have all the baseline positions to get back to your original lens. Clean the helicoids as you wish, remove caked in lumps in the threads with toothpicks, wipe through with tissues followed by lighter fluid/IPA on qtips along the helicoid threads are a good start. Once clean, dry and apply a very thin layer of light/low resistance helicoid grease and prepare to reassamble.



Clean the outside of the chrome index ring and the in/outside of the focus ring with IPA before final assembly.

I haven't got steady enough hands so to ensure easier mating of (particularly the inner) helicoids I found it easier to leave lens face down on a table with mating helicoid facing up - placing the other helicoid on top using gravity minimises any twisted alignment on my part for easier mating.

Ensure that focus ring is dropped over the lens BEFORE reattaching the helicoid

Once the inner helicoid is attached you will get correct position ready to mate the final chrome index ring peice due to the following:

• attach the focus ring to outer helicoid
  With the lens facing down, push the CRC tab to far right to start and lift focus ring and roughly align the CRC tab in the focus ring slot with the prevoius marks. Turn the outer helicoid til it meets the focus ring, turn the lens over and loosely attach the screws to the focus ring. You will need to adjust the helicoid position to meet the CRC tab markings.
• reallign CRC tab to marked positions - this will ensure the correct helicoid position aligned to the focus ring's infinity symbol.
  Using the same approach as adjusting infinity focus, with focus ring attached with loosened screws, use a screwdriver or something with sufficient leverage inserted into one of the focus ring screw haeds and slowly apply pressue onto screw head and rotate the (outer) helicoid behind the ring. This will move the CRC tab. Periodically check that the focus ring is at the infinity position AND up against the infiniity hard stop. You may have to tighten screws, turn to infinity position and repeat to get the correct CRC tab position which is also drawing the outer helicoid up to the correct position.

^{outer helicoid attached, pending securing of focus ring}

With the outer helicoid at the correct position attached to the focus ring, finally attach the chrome index tab peice turning it counter clockwise - the final position of this peice should result in the infinity focus dot and infinity symbol aligned. Finally secure the helicoid keys to their original positions, taking care that they do not rub against the barrel.

Hopefully the helicoids will be easily re-mated and it is only the infinity focus position that may need to be tweaked. With the helicoid keys attached, they should sit aligned to the original marks on the barrel.

This is not a trivial repair or servicing but it is always satisfying to make the lens work like it was new and it'll last another 40years without need for reservicing.