Filters

[Speicus]

I learned from a colleague that not all glass is the same. He worked a summer in greenhouses cutting tomatoes and came back with a deep tan, despite always being "inside" under the glass roof of the greenhouse.
Apparently, greenhouse glass is not "normal" glass; can we be certain that sextant filter glass is?

After wading through many pictures of Freiberger horses, I found the website of the sextant manufacturer - I think I'll send them an e-mail.