Filter—Baader Venus Ultraviolet Pass
Graphs are in nanometers. Visible light is approximately 390 - 650 nm (the human eye can see very weakly into the 700-800nm range). Graphs used by permission of Coastal Optical System.
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At first glance, the original “Venus I” filter doesn’t seem much different than the Venus II filter. Yet field reports from ultraviolet shooters indicate that the infrared-blocking performance of the Venus II is much improved.
Notice the “bump” near 780nm on the Venus I which is not present on the Venus II; this is the source of the infrared contamination that is so disliked— there is often many times more infrared present than ultraviolet, so even a small leak can overwhem the UV image.