Tokina RMC 35-70/3.5: The final project; general notes for servicing lenses

[Andreas Thaler]

To complete my self-training in lens service this year, I serviced this little zoom from Tokina with mount for Nikkor Ai.

All topics discussed so far have become current:

• disassembly/assembly
• cleaning the optics
• external care
• cleaning and re-greasing of the helicoids
• adjustment to infinity

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The Tokina

The two helicoids with old greasing.

After cleaning with Zippo lighter fluid.

I greased sparingly with Castrol LMX Li complex grease.

Lens cleaning:

Isopropyl alcohol on lens cleaning paper and ...

...as a second pass, use isopropyl alcohol on an optics cleaning cloth.

This means that no streaks should remain on the lens.

The result is now clear lenses - and this time only a little dust is incorporated.

All parts cleaned.

Reassembled and also cleaned the outside.

Since I made a mistake when marking the infinity point in the tube, I had to readjust.

Three adjusting screws under the lens rubber coating are responsible for this.

I took measurements again on a construction crane in our neighborhood at a sufficient distance.

The reference was a Nikkor 35-70/3.5 Ai, which confirmed the construction crane boom as an infinity point.

The Tokina was adjusted on my Nikon F3/T, which has been producing flawless results for many years.

A focusing screen E - a focusing screen with a grid - was used for adjustment.

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General notes for servicing lenses

• I now use Zeiss lens cleaning fluid and cleaning cloth to clean internal lenses. Using isoprophyl alcohol or surgical spirit almost always leaves fine streaks that are difficult for me to remove. I get better results with the Zeiss stuff.
• Since I damaged one of the front lenses while cleaning a Minolta 135/3.5 (II), I have become very careful. This one lens was soft on the bottom, which I've never had before. It was quickly scratched. Now I carefully check the surface of each removed lens with the pointed probe to see whether it is resistant.
• JIS crosshead screwdrivers are a prerequisite for older Japanese lenses in order not to damage the screw head profiles.
• Separating helicoids enables thorough cleaning of old grease. However, the separation point of the helicoids and the position for infinity must be marked exactly before disassembly so that the distance scale and infinity settings are correct after assembly. Putting the helicoids back together correctly can be a game of patience, despite the markings. So I now avoid taking helicoids apart and clean/lubricate them when they are assembled.
• Zoom lenses often have plastic plain bearings that enable the movements of the individual rings in the tube. These bearings can break over the decades, especially if the lens has been heavily used. These plain bearings can be replaced, for example from discontinued lenses. Sometimes you are lucky and find replacements in lenses from other manufacturers.
• Sometimes screws in the lens bayonet or inside the lens cannot be loosened. Here you have to be careful not to damage the screw head profile by overtightening it with the screwdriver.
• Be careful when loosening retaining rings for lenses, e.g. the front lens, with the spanner wrench. If the tool slips due to the necessary force, it can cause nasty scratches. There are matte and glossy black paint available to cover if the lens barrel is affected.
• Oily aperture blades are common. The reason for this is old grease on the helicoids, which liquefies and creeps through the tube. As long as the aperture closes properly, cleaning is not necessary. If you want to solve the problem permanently, the lens must be disassembled, completely cleaned and re-lubricated. Otherwise, you only clean the aperture blades when it is necessary again.
• Don't be a perfectionist when cleaning lenses. You can't achieve 100 percent, every cleaning carries the risk of scratches. Minor residues of cleaning agent or a little dust on the lenses don't play a role.
• Fungus has a bad reputation, and rightly so. But it can be removed without leaving any residue if the fungal excretions have not yet etched the lens surface. Fungus is not contagious for other lenses, although this topic is constantly discussed in photography forums. You should store your lenses dry and not too warm. This prevents the development of fungus. And a few small and no longer active mushroom stars on lenses don't play a role.
• Rear lenses are often screwed together as a unit. These units are not always easy to disassemble. Before applying force, you should check the stability of the frame. Pliers usually destroy things, but a rubber blanket for friction can help. If threads are secured with adhesive, a little acetone with exposure time helps. Be careful with acetone if it removes black anti-reflective coatings on the lens edges.
• The exterior of lenses can be cleaned with a mild cleaning foam and a toothbrush if you do not disassemble the lens and place it in a dish soap bath. Oil that comes out of the tube and forms thin films of grease, especially under adjustment rings, can be removed with isopropyl alcohol.
• Before you open a lens, you should be clear about whether you are up to the task. Personally, I would not touch expensive, complex lenses and would hire a competent workshop for the service.
• Further tips and techniques can be found in my repair reports or see recent discussions here in the forum

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All information provided without guarantee and use at your own risk.