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 (outer helicoid) from central 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 outer 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 central helicoid is attached the the focus ring.
TWO separating marks aligned to focus ring's infinity symbol, on the lip of the central helicoid and the edge of the black paint of the outer helicoid/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 central (focus ring) helicoid from inner (optical block) 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 and 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 central 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 central (focus ring) helicod to the edge of the inner (optical block) helicoid - now hold the central helicoid, slowly unscrew the central helicoid with constant but light pressure pulling up to know where it separates. Count the revolutions based on the mark on the central helicoid lip to get a rough idea to reattaching but its not absolutely necessary. When the helicoid separates, locate the previous mark on the central 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).
separating marks, with new mark made on the flat surface of the inner helicoid aligned to the central helicoid's own mark
central helicoid removed, inner helicoid marked with mating position
Lift the focus ring from the rear so it frees the lens over the rear elements.
Cleaning and Reassembly
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.
back, L-R: rubber focus ring | mount, aperture ring | outer helicoid/chrome index tab
front: L-R: focus ring | central helicoid resting on focus ring | inner helicoid/optical block
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 central helicoid
Once the central helicoid is attached you will get correct position ready to mate the final outer (chrome index ring peice) helicoid due to the following:
- attach the focus ring to central 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 inner 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 (central) 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.
central helicoid attached, pending securing of focus ring
With the central helicoid at the correct position attached to the focus ring, finally attach the outer helicoid / 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.
Servicing the CRC
I found that the CRC is easiest to service when the main helicoids are in place - this is because we need stability to know the correct position of the CRC tab.Ensure that at this point the lens has known good focus at infinity - either service the CRC first or after a resassembly and focus recallibration.
- mark the CRC tab positions
There are 4 positions to mark, with CRC tab orientation pointing away from you (at 12o'clock):- the 2 edges of the CRC tab as its installed on the CRC helicoid
- the 2 horizontal planes when the CRC tab is that the MFD (right) and infinity (left) on the optical block internal walls
- remove the CRC tab
Set the lens at MFD and remove the tab.
Mark on the CRC helicoid where the edge of the tab would have been after its been removed. I also tried to collapse the helicoid (at MFD, turning the CRC clockwise) and mark the CRC as it aligns to the open edge where the CRC tab would have been. Note that this may not actually be the fully collapsed CRC position because of the old grease - separate the CRC helicoid, slowly turn CCW - it appears that this helicoid has only one start position
Sit the lens face down on a table and slowly unscrew the CRC. After one revolution, you can put your fingers into the middle openning of the CRC helicoid gently pulling up as you rotate the CRC helicoid - I use a sharp tool in one of the holes to turn which is especially useful if the CRC helicoid grease is sticky as you will find it very difficult to turn this by fingers alone.
When the helicoid separates, mark the inside of the optical block wall to one of the marks on helicoid you made previously - mark arrows on both for mating position
- clean with light fluid and IPA and apply a VERY thin layer of light grease on the CRC helicoid only.
I will reinstall the clean/dry helicoid to get a feel before adding the smallest layer to lubricate - using a NLGI #00 such as NPC BC-13A is good as is JHT #10. - re-install the CRC helicoid
Again, with the lens facing down, use gravity to left the helicoid sit and catch the thread - gently apply downwards pressue on opposite sides of the CRC helicoid to help catch the thread and then turn CW to install the helicoid. Screw this til the helicoid fully collapses and extend a few times to spread the grease to both surfaces. Set the lens to MFD and then slide the CRC tab into the focus ring notch and align the CRC tab inside the CRC marks. Secure the screws. Focus to infinity and the horizontal mark should be aligned. Verify inifinity focus
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 40 years without need for reservicing.
No comments:
Post a Comment