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Nikkor-P 105mm f/2.5 disassembly

On the left, the Nikkor-P 105mm f/2.5 sonnar version, today's project for re-lubrication.


The sonnar version of the Nikkor 105mm f/2.5 came in no less than 13 different cosmetic versions. While the optics are the same, there are small and sometimes large differences to the body of the lens. This guide is for the next to last version made from 1966-1970. There may be other ways to do it, this is what worked for me through trial and error. I'm not a lens repair expert. Take pictures as you go, especially of the helicoid splitting location if you don't want to scribe the lens.

It's important to have the right tools as cross type screws on lenses are Japanese Industrial Standard (JIS) not Phillips. A Phillips screwdriver will strip the heads. I suggest working on an old towel as screws bounce off hard surfaces if dropped, and are too easily lost.

First remove three slotted screws from the focusing ring and slide focusing ring off.


In a lens this old it's not too surprising someone has been in here before, evidenced by the scores that were obviously not made by a professional tech. Scores are a great way to make sure realigning the helicoids goes smoothly - provided your score marks actually line up.


Next remove three slotted screws on the chrome index ring, circled in red here.


Now the chrome index ring slides off and we can see the focusing helicoids and key. The key is the plastic just above the 2.5 aperture mark. It  removed by taking out the visible slotted screws. These screws are only visible while the lens is at infinity focus. The screws can be removed but the key stays in until the helicoid is split.


Now we're to the point of no return. Slowly unscrew the focusing helicoid by turning the ring that the focusing ring was attached to clockwise (looking at the front of the lens). Go slow while pulling the focusing ring away from the body of the lens with constant pressure. It's very important to know where the focusing helicoid separates, because it needs to be threated back on in the same exact spot or focusing will be off when reassembled.
On this copy the scribe marks don't line up with the correct threading location, instead the helicoid scribe is between the two marks on the lens barrel.



The optical block comes out as a unit with the outer focusing helicoid on it. Now be careful with the exposed rear element.



Repeat the process to take the outer helicoid off the inner. On my copy there was no scribe mark for alignment, but these two screw holes lined up by the infinity focus stop.


I use denatured alcohol, a toothbrush and paper towels to clean the threads. Looking nice and clean now.


Now apply grease to the threads. I use a paint brush. In this case I used excess grease because the threads had some damage from being used dry for too long.


This is the hard part. On the optical block is a screw and a tab, both which control the aperture.

Here is the screw.


Here is the tab.


On reassembly, the screw and the tab need to line up with corresponding forks in the lens barrel. There must be some trick to this, but I don't know it.


Take off the rear lens mount by removing five slotted screws.


Gently lift the lens mount and use tweezers to disconnect the aperture lever spring, attachment point seen here.


Set lens mount aside.


Put the key back in place, using a little grease to hold it in place if necessary.
Thread the outer helicoid onto the inner (optical block). Next thread optical block & helicoid to the outer barrel, but stop the moment the threads start. Now the two forks must be aligned with their mate: one for the screw and one for the tab. Unfortunately this is all done blind. Use the inner helicoid to adjust distance as well as the aperture control arm and aperture ring. Four controls, two different directions (on the helicoids) makes for a good time. It's a tedious process and takes me about an hour. Be sure the key stays in place during the process, if it falls out then the helicoids need to be split again. Once the helicoids are joined & tabs aligned, turn the helicoid to infinity focus, reinstall the two screws to hold the key in place, rear lens mount, chrome index ring and focusing ring.

If you have the older version John Cornelius's repair is a good read.

For lubrication I use CRC White Lithium Grease in a spray can. I spray it in a jar and let the carrying agents evaporate overnight. It seems to be the right viscosity lubricant for Nikkor lenses.
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