Hiya,
I suspect a helicoid tensioner is a jig to restore mechanical fit in a worn
helicoid. I don't see anything in the focusing mechanism itself that can
either be replaced or adjusted.
My guess is the helicoid tensioner either: peens or otherwise modifies the
threads very slightly to restore close tolerances; stretches the outer
diameter of the male-threaded section; or, reduces the outer diamter of the
female-threaded section. Probably the first. Probably not something the
average tinkerer could duplicate.
Also, regarding complete disassembly of the lens, it appears to me that
keyed wrenches are necessary to remove lockrings retaining optical elements
just beneath the filter ring and just above the diaphragm. These lockrings
either fit snugly or are secured with threadlocker compound. Can't get 'em
loose with just a screwdriver.
I've fabricated keyed wrenches using leftover brass door keys and brass
stock from the hardware store. A major hassle but sometimes the only way to
do a job right.
I can see some definite complications in the Zuikos that I haven't run
across in other lenses:
1. The checkered rubber ring that must be removed to access the screws
retaining the focus shroud. In most lenses the checkered focus ring is part
of the shroud, eliminating one disassembly/reassembly step;
2. Some optical elements are not permanently mounted in metal or plastic
collars, making careful handling far more important - not only to avoid
fingerprints that might mar the coating, but I suspect that fungus, mold or
mildew can be transferred to the elements through touch. It's probably a
good idea to wear latex or thin vinyl gloves while handling the optical
elements.
OTOH, Zuikos eliminate a couple of disassembly complications present in
Canon FD lenses:
1. It isn't necessary to disassemble practically the entire damn mount when
going through the rear;
2. The filter ring shroud (the doodad with the lens info printed on it) can
easily be removed using a screwdriver. Some other lenses don't have keyed
slots, making it necessary to use grippy rubber tipped tools to loosen those
rings.
Regarding fungus, mold and mildew removal, I'm experimenting with a couple
of household cleaners like Oxy-Clean, an oxidizing cleanser that doesn't
contain common bleach (sodium hypochlorite). I'll report back whether it
helps, harms or does nothing.
I'm copying this reply to the OM list for future reference.
===========
Lex Jenkins
===========
From: Dogbreath <hopi@xxxxxxxxxx>
To: lexjenkins@xxxxxxxxxxx
Subject: Re: [OM] Helicoid grease (was:50/2 macro vs. 90/2 macro)
Date: Sun, 7 Jan 2001 09:31:33 -0500
Lex,
Thanks for sharing what you're learning about focus damping.
I'm gonna dig into a dead Zuiko lens to learn about this myself...
John Hermanson refered to something called a helicoid tensioner. That, I
presume, is as important as the grease for the adjustment.
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