wideopeniris
Newbie
Having now obtained a second copy of the Canon S Series 100mm F3.5 Lens with milky fog on the middle negative element, I was inspired to finally work out why they are foggy.
My first lens, someone had attacked the element and it had fairly deep scrtaches on as well as the speckely fog. For those unfamiliar, you will see plenty of these lenses advertised for sale with 'fog' or 'haze'. You may be tempted to think 'Oil Haze - an easy clean' but this is not the case. Having tried all solvents and other normal cleaning techniques, the Haze is stubbornly unaltered. The surface appears covered is milky blobs on both faces.
So I took the trouble to put the lens element under a proper microscope to see what was going on.
The dark spots are in fact the original (single) coated surface which has degraded is a fairly disastrous manner. Unlike fungus which starts at a dust spot and then has filaments of surface damage, this effect is everywhere across the lens surface. The coating has degraded due to some chemical attack, possibly from the glass itself or from something trapped in the lens body. A shot nearer the edge of the lens makes this clear:
What we see here is a ring that was underneath the metal mount ring. Here the coating is uniform and largely unaffected. Also you can see clearly that all the marks are formed of a sheet of uniform thickness which is crazed and damaged, probably from chemical attack or failure to adhere correctly in the first place.
Needless to say that this is unrecoverable without (probably very difficult) re-polishing and recoating of the element. Therefore I would advise against picking up these fogged lenses cheap, hoping they will clean up, as the promblem is not reversible, as it might be if it was oil haze. I have two of these - the earlier one is chrome and black, and the later is all black - both have the same basic trouble, although the older one was exacerbated by someone elses less gentle approach.
Anyone think they have a workable and cost effective solution to fixing this problem?
Opions welcomed.. anyone else seen this with other lenses?
My first lens, someone had attacked the element and it had fairly deep scrtaches on as well as the speckely fog. For those unfamiliar, you will see plenty of these lenses advertised for sale with 'fog' or 'haze'. You may be tempted to think 'Oil Haze - an easy clean' but this is not the case. Having tried all solvents and other normal cleaning techniques, the Haze is stubbornly unaltered. The surface appears covered is milky blobs on both faces.
So I took the trouble to put the lens element under a proper microscope to see what was going on.

The dark spots are in fact the original (single) coated surface which has degraded is a fairly disastrous manner. Unlike fungus which starts at a dust spot and then has filaments of surface damage, this effect is everywhere across the lens surface. The coating has degraded due to some chemical attack, possibly from the glass itself or from something trapped in the lens body. A shot nearer the edge of the lens makes this clear:

What we see here is a ring that was underneath the metal mount ring. Here the coating is uniform and largely unaffected. Also you can see clearly that all the marks are formed of a sheet of uniform thickness which is crazed and damaged, probably from chemical attack or failure to adhere correctly in the first place.
Needless to say that this is unrecoverable without (probably very difficult) re-polishing and recoating of the element. Therefore I would advise against picking up these fogged lenses cheap, hoping they will clean up, as the promblem is not reversible, as it might be if it was oil haze. I have two of these - the earlier one is chrome and black, and the later is all black - both have the same basic trouble, although the older one was exacerbated by someone elses less gentle approach.
Anyone think they have a workable and cost effective solution to fixing this problem?
Opions welcomed.. anyone else seen this with other lenses?