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Nikkor 105mm f/2.5 AI-S disassembly

On the right, the Nikkor 105mm f/2.5 AI-S Xenotar version, today's project for re-lubrication.

Unlike the sonnar version of the Nikkor 105mm f/2.5 which came in no less than 13 different cosmetic versions over 12 years, the AI-S model came in one version for 24 years. 

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 pull the lens hood forward and focus to to the minimum focus distance. This reveals three small slotted screws. Remove and set aside.

Note the size of these compared to lens mount screws, don't drop one.

The built in lens hood unscrews from the optical block counter-clockwise (when viewing from the front). Then the whole optical block simply lifts out as one unit, very slick. Set aside somewhere safe as the elements are exposed. If you need access to the center element it's done by unscrewing the block in the middle, counter-clockwise.

Flip the outer casing over and remove three JIS lens mount screws & set lens mount aside.

Inside are two metal keys for the helicoid. Remove the small JIS screws for each key and set aside, paying attention to which key came from which guide. Over years of use they work better where they are worn in and can affect focusing if switched when installed.

Now we're to the point of no return. Slowly unscrew the inner focusing helicoid. Go slow while pulling the inner helicoid away from the outer body 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.

There are no scribe marks on this copy, but I found the helicoid separates where the notch (blue pointer) lines up M in Made in Japan. Set aside inner helicoid. See the old gummy lubricant?

Take off the rubber focusing ring. It's important to make a scribe mark for infinity focus.

As a random aside, in the world of Nikkor lenses there are many comments about the glory days of AI-S manual focus lenses and their quality construction, and bemoaning of that fact that some lenses like the new 18-55mm zooms have parts held together by scotch tape. Here on the 105mm f/2.5 AI-S the focusing ring and distance scale are held together by scotch tape, showing a decline from the original 105mm f/2.5. On the other hand the older lens had one plastic key for the helicoid while this one has two metal keys.

Now remove scotch tape and unthread the outer helicoid. Go slow while pulling the outer helicoid away from the outer body 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. Note where it separates from the chrome index ring.

From left to right, the focusing ring / outer helicoid, distance scale ring and chrome index ring / aperture ring.

Clean all helicoid threads and apply grease of choice. I use denatured alcohol, a toothbrush and paper towels to clean the threads. Thread outer helicoid and distance scale back on. Where you line up the scribe mark & distance scale dictates infinity focus. I adjusted the infinity focus to allow the lens to focus past infinity, as I prefer this to a hard stop when using the Sony A7. 

Adjusted slightly from previous picture, note how scribe mark is dead on infinity not slightly past it. Tape with infinity set to desired point and focus to minimum focus distance.

Install the inner helicoid. Once the threads start stop, flip the lens over and watch through the rear, lining up the key mount locations with matching slots. Install keys and rear lens mount. Set the optical block back in. If you're having trouble lining things up, just set the aperture to f/22 and adjust the aperture tab on the lens block to fully closed.

All back together except the focusing grip and lens hood.

Install the lens hood, and if you want hard stop infinity focus dead on leave installing the rubber focusing grip for last, as it will take a few trys adjusting and reapplying the scotch tape to get it perfect.

Now celebrate with a beverage of choice! It's much easier than the older Nikkor-P 105mm f/2.5 but easier to mess up the infinity focus and get the helicoids threaded wrong, so pay attention.

I started with Tomas's tutorial and explored from there for splitting the helicoid.

For lubrication I've been using 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 AI and earlier lenses, but too thick for AI-S.

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