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Re: [OM] Damping Fluid

Subject: Re: [OM] Damping Fluid
From: Joe Gwinn <joegwinn@xxxxxxxxxxx>
Date: Wed, 26 Nov 2003 10:22:11 -0500
At 9:23 AM +0000 11/25/03, olympus-digest wrote:
>Date: Mon, 24 Nov 2003 23:57:02 -0800
>From: Jim Brokaw <jbrokaw@xxxxxxxxxxx>
>Subject: Re: [OM] Damping Fluid
>
>on 11/24/03 12:23 PM, fred42@xxxxxxxxx at fred42@xxxxxxxxx wrote:
>
> > Hello all,
> > 
> > Quick question. What would be the most suitable thing to use
> > for damping a movement in a lens?
> > 
> > I ask it in relation to my recent
> > Nikon shift lens conversion. It has a tendency to 'droop' when shifted all
> > the way up. The mechanism is question is a screw driven plate/groove that
> > carries the lens body. Would I do best to apply it to the screw or the
> > plate?
> > 
> > Dan S
>
>Fargo Enterprises on the web (do a Google search) sells a variety of greases
>that are used for dampening lens movements. I've had good success with
>ordinary greases such as used for bicycle bearings, auto grease, and some
>'Dow Silicon High Vacuum Grease' which was intended for use in vacuum
>chambers of wafer-fab equipment. They key is to get the right 'stiffness' (I
>think called out by NGLI spec...?) and that depends on the clearances and
>area of contact involved...

I have some of the Dow Silicon High Vacumn Grease.  It's *very* stiff, and 
would probably make a lens impossible to focus if applied to the focus 
helicoid.  On a shift lens, where it's two flat plates sliding on each other, 
it might work, but still it seems too stiff to me.

Putting grease on the screw allows one to use a much stiffer grease.

Vacumn greases are not very good metal lubricants, especially the silicon 
greases, being intended for ground glass joints ant the like.

Bearing greases (bicycle and auto) tend to bleed oil, which could be a bad idea 
inside a lens, depending on the construction details of the lens.


>There might be a way to shift the plate to load the gear threads, that would
>stabilize it until the thread wore more... maybe hundreds or thousands of
>movements later. Or you could deform or peen the threads to cause some
>interference, but I would recommend getting a duplicate/replacement part
>before trying any kind of 'mechanical fix'.

If those mechanical parts are made of aluminium, which is likely, I wouldn't 
use the mechanical method.  Aluminium rubbing hard on aluminium tends to gall 
and weld.


Joe Gwinn


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