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Caltar lens bubbles



 
 
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  #1  
Old October 2nd 04, 04:11 AM
Tom Phillips
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Posts: n/a
Default Caltar lens bubbles

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

Richard Knoppow wrote:

"Bob G" wrote in message
But he also noted that these are Schneider lenses and
display the typical Schneider problem of bubbles in the
blackening between lens elements and barrels.


Its caused by flaking of the anti-reflection paint on the
edges of the lenses. This is applied to lenses where there
might be total internal reflection from an edge, not all
elements require it. The paint is also used to seal the
edges of cemented lenses although this is not the issue it
was when Canada Balsam was used for cementing.
I don't know why Schneider had this problem. It seems to
affect lenses made from the mid 1950's to about the mid
1960's. Its the sort of thing that takes so long to show up
that it may not be known to be a problem for a very long
time.
The effect is of bubbles at the very edge of the lens.
Careful examiniation will show that these are not actual
bubbles in the lens. This is a problem only if enough light
is scattered from the edge to increase lens flare,
generally, it is of no significance.

The problem can be fixed by disassembling the lens,
cleaning off the old paint, and repainting. The best paint
currently available for this is sold in the USA as Krylon
Ultra-Flat Black. It comes in spray cans so a small amount
must be sprayed into a small container for use. Apply it
with a small brush or a cotton swab. It must be thoroughly
dry before the lens is reassembled. At one time a product
was made by 3M (I think) called Velvet especially for lens
anti-reflection paint but its been off the market for years.
This stuff had the advantage of not outgassing. Outgassing
can be a problem when paint is used in sealed lens cells
because it can cause a haze to form on the lens surfaces. In
fact, such a haze is quite common and is visible when a
flashlight is shown through the lens. Even a slight haze
will destroy image conrast. Its easy to clean off but the
lens must be disassembled to do so, a PITA.

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

  #2  
Old October 2nd 04, 04:49 AM
jjs
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Posts: n/a
Default

"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.


Can you hold the lens a little closer here, Tom? I can't see it.

Fine lines are often fungus.


  #3  
Old October 2nd 04, 04:49 AM
jjs
external usenet poster
 
Posts: n/a
Default

"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.


Can you hold the lens a little closer here, Tom? I can't see it.

Fine lines are often fungus.


  #4  
Old October 2nd 04, 06:49 AM
Richard Knoppow
external usenet poster
 
Posts: n/a
Default


"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.


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



  #5  
Old October 2nd 04, 10:16 PM
Tom Phillips
external usenet poster
 
Posts: n/a
Default

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.

 




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