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Re: [OM] Catch all solution for stuck aperture blades

Subject: Re: [OM] Catch all solution for stuck aperture blades
From: Chuck Norcutt <chucknorcutt@xxxxxxxxxxxxxxxx>
Date: Sun, 31 Jan 2010 10:59:17 -0500
Well, it must be entrainment with violent evaporation because the method 
works for me and I have never used a tissue or any sort of absorber.  I 
also violate your rule of not working the diaphragm but I do see the 
logic of your point.  I work it as vigorously as I can as soon as it 
starts to move if stuck in place.  There's nothing going on except 
evaporation of the solvent and all the oil soon disappears.  I must also 
take exception to your point about the oil not coming from viscosity 
breakdown of the focusing helicoid.  First, that's the only place 
there's any grease to begin with and any lens I've found with this 
problem tends to have a rather undamped focusing ring.  I would expect 
that much of the interior of the lens barrel also has a coating of 
oil... which is why the problem will eventually return.

But I've never done this on a lens worth more than about 30 bucks.  If 
something fails in the process that's OK.  So far, no problem.

Chuck Norcutt


mes9120 wrote:
> None of the oil will evaporate with the solvent.  A little might be
> entrained if the evaporation is violent.  I say this from applying my
> Chemical Engineering and Physical Chemistry degrees to 33 years in
> the petroleum industry including refinery and research work--and
> having cleaned several lens diaphragms.
> 
> Lighter fluid is widely used and it must be OK, but my choice is
> Coleman Brand camp stove fuel.  When I tested some it proved to be
> nearly pure n-heptane and evaporates without leaving any residue.
> Test any solvent you choose for residue, and do not get natural oil
> from your fingers (sebum) in the solvent.
> 
> I hold the diaphragm at an angle while using a medicine dropper or
> hypodermic syringe to apply solvent at the top with a lens tissue at
> the bottom to absorb the solvent now containing oil.  It takes a lot
> of flushing.  A cotton swab (Q-tip) is handy for absorbing the
> washings but lens tissue is less likely to leave fibers behind.
> 
> Be cautious about activating the blades when they are wet with
> solvent.  Due to the surface tension of the solvent force is required
> and something might break.  If you break off one of the little pivot
> knobs attached to the blades you are in deep do do.
> 
> Sometimes there is no oil evident on a sluggish diaphragm because
> lubrication of the pivots has become gummy either by degradation of
> the lube or collection of dirt in the lube.  I have read lens service
> manuals instructing lubrication of the diaphragm pivots.  Applying
> too much is very easy and eventually the excess will migrate to the
> blades where surface tension impairs their swift action.  Keeping the
> lens cool (room temperature) minimizes the migration of the oil.
> 
> I do not oil the pivots of diaphragms I have cleaned.  Surely the
> metal on metal friction of the pivots will eventually cause wear and
> failure, but the loads are so light it may take nearly forever.
> 
> I do not accept the conventional idea that oil on the diaphragm comes
> from the lube on the zoom mechanism or the focusing helix.  I have
> found focusing grease on the edges of nearby glass elements.
> 
> Do not apply solvents such as MEK, Acetone, or Alcohol to diaphragm
> blades.  Some blades are made of plastic and polar solvents may warp
> the blades.  Plastic blades were used on some Agfa/Ansco 120 folders
> and probably others.
> 
> Good luck,  S. Mel
-- 
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