"PGG" wrote in message
newsan.2004.08.05.00.27.33.962000@NO_SP_A_Myahoo .com...

I bought a spanner wrench to remove a rear retaining ring
from my
Ilex-Calumet 215mm f5.6 lens. This allow me to get to
this cell, however
the fog is _inside_ the cell and not on the accessible
surfaces. It is
pictured at the link below:


http://pg.photos.yahoo.com/ph/papago...&.dnm=3376.jpg

It looks like there are 2 pieces of glass sandwiched
together somehow.

I don't think cement is used because I called my local
repair shop, for
which I got a previous estimate of $78 to clean, and asked
if they
uncemented/recemented cells to clean them. They said they
do _not_ do
this, and that if they gave an estimate for my lens, then
they are able to
clean it regardless. Unless they didn't realize the
extent of the fog,
then I believe these glass pieces are attached some other
way.

Any ideas? Should I give up and pay the $78?

-PGG

I replyed via e-mail about this. Its hard to tell from
the photo but it looks like a cemented lens. The Ilex lens
described is a "Plasmat type. These have two cemented
elements facing the outside of each cell and a single
element inside facing the stop. When some types of synthetic
cements begin to become degraded they look hazy. Sometimes
they even have an "orange peel" look when examined using a
strong loup.
Recementing lenses can be reasonably simple and done
yourself. Most cemented elements are made with precisely
ground edges, when the edges are lined up and clamped the
lens is aligned. Cement is available from Summers Optical.
The easiest to use is probably their Ultra Violet curing
type UV-69 This will cure with a BL BLB UV lamp. The
technique is described on their web site.
http://www.emsdiasum.com/Summers/opt...ts/default.htm

There are a few technicians who will recement lenses.
John van Stelten has been offering this service for a long
time and has a good reputation, however, he is expensive.
Some older lenses are not worth the cost of recementing
them.

The Focal Point
John Van Stelten
1017 South Boulder Road
Suite E-1
Louisville, CO 80027-0027
Tel.- 303-665-6640
Fax - 303-665-3803
http://www.411web.com/F/FOCALPOINT/


I've recemented a number of lenses using Summers binary
(heat curing) cement. This worked well but the UV curing
stuff is easier to use. The UV-69 type has the advantage
that it is not considered a hazardous material for shipping.
The suggested method of decementing elements cemented
with synthetic cements is to boil them apart in a special
oil. The oil is also available from Summers and is not too
expensive but it must be shipped as a hazardous material
which about doubles the cost. Another method which works on
many lenses is to soak them in Methylene Chloride. This is a
common solvent used in paint removers. It may take days for
the solvent to penetrate. If this works its safer for the
lens because there is no danger of heat shock which can
cause chipping or even break the elements.
Very old lenses, cemented with Canada Balsam (the stuff
that turns yellow or brown at the edges) will come apart
with gentle heat. Its often suggested that they be heated on
a hot plate but I find they will come apart in heated water.
Put them in cold water and heat until they come apart. The
heat needed is well below the boiling point. Lenses
originally cemented with Canada Balsam should be recemented
with a modern synthetic.
The hardest part of recementing is getting the glass out
of "burnished" or "spun-in" mounts. These were made with a
thin lip of metal which was burnished down around the
periphery of the lens. This is an excellent mount as far as
accurate centering and protection of the glass but is
difficult to undo. I have had some luck in prying up the lip
so that it can be re-used but very often it will break or
become wrinkled. The usual technique is to machine it off in
a precision lathe, thread the back of the mount, and make a
back retaining cap. All fine if you are a skilled machinist,
I am not. It is also possible to reinstall the lens using
epoxy cement around its periphery. Most Tessar type lenses
have the back component mounted this way. Recementing the
elements is much easier than dealing with the burnished
mount.
When a lens is recemented the anti-reflection paint must
be removed. After cementing it must be replaced to prevent
total internal reflection from the edges (some single
elements do not need the paint). At one time an excellent
paint called Velvet was available but its been off the
market for many years. The best current paint is Krylon
Untra-Flat Black. This comes in spray cans. Its used by
spraying some into a small container and applying it with a
brush. Its also good stuff for painting the interiors of
lens cells and and generally on other surfaces which should
not reflect light. The paint also acts as a seal for the
cemented edges of the lens. I think one reason that some
brands of old lenses seem to be more prone to degredation of
the Canada Balsam cements is the variation of the
effectiveness of the sealing quality of the anti-reflection
paint. For instance, old Zeiss lenses seem to more resistant
to cement problems than old Bausch & Lomb lenses.
While the effect of oxidizing or crystalized Canada
Balsam is pretty familiar the effect of degraded synthetic
cements is less so. That is partly because they are much
more stable than Balsam but also because the effect may be
harder so see. Sometimes is appears to be large bubbles
between the elements, this is due to separation of the
cement and probably due to poor surface perparation or
curing problems during manufacture. Another effect, and one
that may be difficult to see if you don't specifically look
for it is the slight haziness the cement develops. This is
visible when a flashlight is shown directly into the lens.
Sometimes its more visible by reflected light than
transmitted light. The effect on lens performance is to
destroy contrast. Even a very slight haze has a surprizingly
large effect on contrast. When shopping for used lenses its
a good idea to carry a loup and a small flashlight with you.
These can show up cement problems, fine scratches, gouges,
haze, dirt, and fungus. While even a very clean lens can be
awful its also true that the best lens can be ruined by any
of the above.


--
---
Richard Knoppow
Los Angeles, CA, USA