New answers tagged infrared
Maybe. The product that selectively blocks a specific defined range of EM (electromagnetic) radiation is referred to as a "notch" filter. They are made from various materials including quartz, germanium, and glass among other substrates and materials. Hit the optical catalogs to locate the likely stuff you want. Here's a bit of related arm-waving. As it ...
Try Edmund Scientific/Optics for prototyping materials.
The large and nearly perfect circle(s) often found in photos taken with an IR filter are often referred to as "hotspots", and they are mostly caused by internal reflections in the lens and filter combination. To my eye, the most obvious spots in your example image are these sorts of hotspots. The internal reflections are not absorbed by all len and barrel ...
I have seen the same issue and found that sealing the filter to the filter folder (Lee in my case) made the spots go away. I think that because the IR filter stops so much light and therefore the expose time is so long then any light creeping in through tiny gaps between the filter and its holder will allow any small specks of dust on the back of the filter ...
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