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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