I Have a white-light metal on glass solar filter made by Thousand Oaks, which I acquired for the 1999 eclipse.
Inspection still reveals no pinholes or scratches (it has always been kept in a padded case) so my only concern is if these kind of filters have a known lifespan before they allow too much light to pass, especially in the IR & UV.
Visually, the image seems no brighter than it was 22 years ago, as I still use it with the same 90mm Mak that I bought it for, although memory is a funny thing with humans!
Does anyone have any knowledge on this subject. Thanks…
I’d be very interested in finding out too as I have a Seymour white light glass solar filter which has small pinholes in which I can’t remember seeing there before. I too wonder if they have a shelf life?
I also have a Seymour Solar filter used on a C 90 and 90 mm F5.5 Refractor. bought from Rother Valley Optics , some fairly long time ago. The Instructions give advice on checking for Pin holes (Hold the filter with the inside towards you and outside towards a 60-100 watt soft white light bulb.two feet away from the bulb. Any pin holes can be blocked using a fine point felt marker , small drop of paint or typing correcting fluid. AS many as 20 touch ups per clear aperture inch can be made with no adverse effect on performance). Seymour’s then say that pin holes are rare in their quality products. Hope this helps
Very interesting regarding the advice from Seymour, mine has a cluster of 8 or 9 pinholes. I would have thought felt marker on glass would rub off. Getting a good density of correction fluid might be interesting as the last one I used was very watery.
Ive gone over to using a Lacerta Herschel wedge but also have Baader solar film filter which has no pin holes in it at all.