Topic summary
Wratten filter
Extracted from the Wikipedia article Wratten number.
History and use
Wratten filters are often used in observational astronomy by amateur astronomers. Color filters for visual observing made by GSO, Baader, Lumicon, or other companies are actually Wratten filters mounted in standard 1+1⁄4 in (32 mm) or 2 in (nominal, 48 mm actual) filter threads. For imaging interference filters are used. Wratten filters are also used in photomicrography.