Thanks Richard.

"Richard Knoppow" wrote in message ...
"Tom Phillips" wrote in message
om...
Can anyone describe what this bubble effect looks like,
what to look for if this were to be visible or be a
problem?
The lens I'm looking at shows some fine hair-like or other
particles in the elements or along the edges when
examining
a wide open aperture. I have always noticed very small
particles (flaking?) between Schneider lens elements but
never noticed an image issue.

Tom Phillips

When the edge paint loosens up it looks like bubbles right
at the edge of the lens, out of the clear aperture. What you
see is light reflected from the edge where the paint is not
longer touching the edge surface. The edge paint usually can
not get into the air space so when black flakes appear on
inside surfaces they are usually falking anti-reflection
paint from the inside of the cell itself. In general this
does not affect the image unless there is a lot of it.
Hair like filiments are often fungus. Fungus can also look
like little wads of cotton. Fungus should be removed because
the metabolic products of the fungus can etch the glass and
there is no fix for that. Sometimes extended exposure to
direct sunlight or other very strong Ultra-Violet light will
kill the fungus but the lens cells should really be opened
and the fungus cleaned out. Since the cells should be air
tight fungus may indicate that there is some leak somewhere
letting the fungus in. Fungus is often found between the
cemented elements of lenses cemented with Canada Balsam
because it is a good culture medium. Such lenses must be
recemented. Canada Balsam ususally fails a the edges
becoming oxidized. This results in a yellow ring at the lens
edge. If it dries out sufficiently it crystalizes there the
crystals being quite obvious. I think the reason some lenses
are more suseptible to this than others may be the quality
of the anti-reflection paint on the lens edges which also
acts as a seal for the cement. Modern lenses are cemented
with synthetic cement, which came into use about 1940.
However Canada Balsam continued to be used until the
mid-1950's if not even later.