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[OM] Re: M42 lens repair

Subject: [OM] Re: M42 lens repair
From: Chuck Norcutt <chucknorcutt@xxxxxxxxxxx>
Date: Fri, 20 Oct 2006 16:11:00 -0400
You can call some local shops but if you find someone to repair it the 
price may well be prohibitive.  Since the lens cost a pittance perhaps 
you'll be willing to give it a try yourself.  You first need to satisfy 
yourself that the problem is not due to impact damage which has gotten 
the outer focusing helicoid out of round.  If, as you suspect, it's just 
dried out grease you need to remove the outer helicoid, clean both 
helicoid surfaces, regrease with a small amount of wheel bearing grease 
and reassemble.  That's the tricky part.

I don't know anything about this lens but you'll probably be able to get 
the helical apart fairly easily.

1) remove the "name ring" inside the filter threads.  It's possible 
there are pin holes or slots in the ring 180 degrees apart to allow use 
of a (apologies to the UK guys) spanner wrench  with pins or slotted 
drivers.  More likely you'll have to unscrew it with some sort of 
friction tool.  You need a cylindrical tool that's hollow in the middle 
(at least enough to clear the glass) and has a grippy rubber surface on 
the business end.  A tour around the house or the hardware store might 
find something that can be pressed into service.  Some options:  a tin 
can, a furniture leg cup, a PVC pipe fitting, a wooden closet rod 
holder.  You get the picture.  I've used all of these in various sizes 
often with a piece of wide, grippy rubber band rubber cemented to the end.

Make sure the business end isn't touching the glass, press down hard on 
the name ring and unscrew counter-clockwise.

2) once the name ring is off you'll likely find 3 or 4 screws underneath 
that are holding the filter ring in.  Remove the screws and the filter ring.

3) that should allow you to remove the front lens group either by 
removing screws or more likely unscrewing the whole lens cell in a 
counter-clockwise direction.

4) now you should be able to see how the inner and outer helical 
threaded barrels fit together and how the stop mechanism works at close 
focus position.  There will also be an adjustable stop mechanism at the 
infinity focus position which needs to be adjusted for infinity focus if 
it gets out of whack.  The two barrels unscrew until they're stopped by 
some sort of pin or other stop device at the closest focus position with 
the lens barrel fully extended.  Depending on how it works it may be 
necessary to roll back the rubber ring on the barrel which may reveal a 
screw that controls the stop.  You're on your own here.  I have no idea 
what you'll find except that you'll find something blocking the two 
halves completely unscrewing.  Otherwise the front and rear halves of 
the lens would separate when focusing close.  Some lenses have their 
infinity focus position adjusted with tape.  In this case there is a 
fixed stop on the rear half of a two part lens lens barrel.  The front 
half that turns on the helical threads is joined to the rear half by a 
ring of tape running under the rubber focusing ring.  Adjustment is 
carried out by removing the tape, rotating the front barrel and then 
retaping the parts together.

5) Now be very careful.  You need to mark the point where the helical 
threads mate before you separate them.  You may need to use something 
like a sharp scribe to put mating marks on the inner and outer helical 
barrels.  These two barrels can probably go back together by starting on 
any of the half dozen or so thread pairs BUT ONLY ONE OF THEM IS 
CORRECT.  If you don't get the threads mated properly you'll never see 
infinity focus again.  Also, when putting the helical threads back 
together you'll find that it will likely try your patience but you need 
patience.  Unless the two barrels are held absolutely squarely aligned 
with each other the threads will refuse to mate.  Make sure the children 
and others with sensitive ears are not around as the helicals will 
require lots of verbal abuse before they finally succumb.  But persevere.

6) clean the helical surfaces thoroughly with solvent and a small, fine 
brush.  An old toothbrush might be a good tool.  Maybe a kid's 
toothbrush would be better as it's a bit smaller.  Regrease with a very 
light coat of wheel bearing grease.  The start cussing as you try to get 
the helicals to reengage.

7) I haven't done this for a long, long time.  Maybe someone else has 
some more tips or can correct me if I made an error.

Chuck Norcutt

Ali Shah wrote:

> I received a nice little Tokina 105 F2.8 M42 mount
> which I intended to use with my E-500 and M42 adapter.
> The Tokina is an older lens which had been distributed
> by "NPS" (a Canadian outfit). It is a 'preset' type of
> lens...has to rings that control aperture. The problem
> is the focusing ring is so damn stiff that the lens is
> not useable. I believe the lens sat in its original
> box for 30+ years and the lubricant dried up. Is there
> someone that can repair this lens? I am looking for a
> very inexpensive repair because the lens cost a
> pittance.
> 
> Thanks.
> 
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