[LargeFormat] Lens cleaning advice required

[Richard Knoppow]

----- Original Message ----- 
From: "Gavin Hubbard" <ghub005@xtra.co.nz>
To: <largeformat@f32.net>
Sent: Friday, August 08, 2003 7:38 AM
Subject: [LargeFormat] Lens cleaning advice required


> Hi Lads
>
> I picked up a fairly cheap (around $360 USD including
caps) Rodenstock
> Grandagon 90mm f6.8 from a local seller recently. Apart
from some
> delamination around one of the internal elements it seems
to be in a fairly
> reasonable condition. I've shot some film through it and
it seems to be in
> order.
>
> Homever there are some faint oil/grease marks on the glass
that I'd like to
> remove. I'm guessing they're probably fingerprint
residues(?)
>
> Is there an easy way to remove this residue? I tried using
an off-the-shelf
> window cleaner but it left some streaking on the glass
(removed with
> water). Any advice on "LF lens cleaning best practice"
would be greatly
> appreciated.
>
> Best regards,
>
> Gavin
>
  Standard window cleaners and lens cleaners are weak
ammonia solutions. Window cleaner is Ammonium hydroxide,
lens cleaner ammonium carbonate. Neither is always
effective. A better cleaner is the newer "streak-free" type
window cleaner. These have butyl alcohol in them. I would
try one of these before trying one of the solvents below.
  Isopropyl alcohol is an effective solvent for lens
cleaning and fairly safe. So is methyl alcohol, but it is
more likely to damage paint. Methyl alcohol is widely used
in assembly work currently.
  The old standard for cleaning during assembly is Acetone,
but it must be used with great care on assembled lenses
because it will dissolve paint and also some types of
optical cement. Clean the lens with the surface pointing
down to avoid solvent getting into the gap around the edge
of the element.
  Use a lint free tissue like Kimwipes. Put the cleaner or
solvent on the tissue, never directly on the lens. For very
dirty lenses its best to blow them off first. Then lay the
wet tissue on the surface and pull drag it off sideways
without pressure.
  Particals which do not blow off can often be picked up
with a look of sticky tape, the same technique as getting
lint off of clothes. The idea is to avoid any pressure or
lateral motion which might cause scratching. Use each tissue
once only and toss it out.
  Don't use a re-usable brush, make one-use brushes from the
tissue. Roll it up into a cylender, tear it in the middle
and fold the feathered ends together. Use that once and toss
it. Kodak Lens Cleaning Tissue works very well for making
brushes since it feathers well. However, Kimwipes are better
for general use since the Kodak tissue tends to fall apart
when wet.
  Inside surfaces can be cleaned as above, the main problem
is getting to them. While there are some standard methods of
assembling lens cells different manufacturers use different
approaches. Most have some sort of threaded retaining rings
but one finds threaded collars, etc. Schneider likes to use
really tiny set screws.
  Be very careful in disassembling a complex lens. Some
include spacers or shims. Make sure you note where they came
from and which direction they were facing. Also, sometimes
one finds elements which are almost the same on both sides.
Their orientation is important. Find some way of noting
their orientation.
  Missing edge paint and internal cell paint can be replaced
with Krylon Extrra-Flat Black. Its in a spray can but you
can spray some into a small bottle and apply it with a
brush. The best paint for lens edges "Velvet" was
discontinued some years ago. I think it was made by Bausch &
Lomb.
  I have found occasional lenses with what looked like
droplets of oil on inside surfaces. Finder lenses on
Rolleiflexes seem prone to this. I have no idea where it
comes from but it comes off easily.
  The other common problem with older lenses is haze. I
suspect this is something evaporated from the
anti-reflection paint in the cell but don't actually know.
In any case it comes off with any lens cleaner. My chrome
barrel Schneider Symmar had pretty thick haze in it so its
not just very old lenses that it occurs in.
 AFAIK, ROR is just conventional cleaner of the streak-free
type. Much cheaper to get the stuff from the grocery store.
---
Richard Knoppow
Los Angeles, CA, USA
dickburk@ix.netcom.com