The Baader Venus filter blocks the entire spectral region from 200nm to 1500nm except for a very narrow bandwidth from 300nm to 400nm in the far violet. Transmission efficiency reaches 80% at the peak. This filter makes it possible to image cloud detail on the surface of Venus.
Please Note: The Baader U-Filter is specifically for digital imaging (digital SLR, webcam or CCD). Since visual perception stops at about 400nm (380nm if you're lucky), the light transmitted through the filter is not detectable by the human eye. Do not purchase this filter for visual use! Also note that the colors in the photo at left are the true reflected colors of each side of the filter and are the result of the different dielectric coatings used on each surface.
The accompanying photograph of Venus, taken by M. Rietze just 2 days before transit, shows the cusps enclosing two-thirds of the planet's circumference.