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#1
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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
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"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
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"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
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"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
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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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