Excerpt: This filter is for scientific purposes or experimental photography. It cuts out all visible light, but, and that's important, as far as I tried, it lets through the infrared "light". Since the CCDs and CMOSs are sensitive to IR and UV, they have a cutout filter for these radiations, so, in order to use this filter for UV photo, one must use both a cutout IR filter and the 403 UV filter.
Excerpt: If you own a full spectrum or converted camera, and you have already mastered the art of infrared, you owe it to yourself to explore the unique world of ultraviolet. This filter blocks out all visible light and allows in only UV, which causes very dramatic colour effects. If you enjoy getting technical, or want to try something very different, this filter is something you will get alot of enjoyment from.
Excerpt: Using the filter with an IR modified K7 (clear conversion with hot filter removed). The filter is very dark, but using live view allows for composition. Handheld shots are possible in good lighting conditions, though it did take a moment to find the proper combination for good exposure due to the file factor.
Pros: Clear Optics, Firm Mount, Strong Construction
Summary: Any time I purchase a new lens, a protection filter is a mandatory lens accessory for me. I won't begin shooting that lens without the protection afforded by a good filter. B+W filters are among the best quality filters: well made, clean glass, good rep. The question for me isn't whether or not to get a UV filter, but how can you drop serious $$ on a lens and not protect it with a basic filter?