While Venus shows no surface structure in the visible spectral range, dark clouds and bands can be photographed in the UV spectral range. These structures are located in the upper atmosphere of the planet and rotate once around the globe in about 4 days. If the phase of Venus shows it illuminated over 50 degrees, a complete map of the cloud structures can be completed within 4 days.
A UV filter is needed to photograph the clouds on Venus which blocks wavelengths above 400nm completely. Astrodon makes the best filters on the market for this. An interference filter, it has a higher transmission than the UVBRI glass filter set often previously used. The Astrodon filter also blocks the infrared. Cheaper filters often let IR through, which can lead to reduced contrast and blurring of the planet's edge. The UV-pass filter has filter threads and hence fits into standard eyepiece barrels and camera adapters. To achieve optimal results, a reflecting telescope and UV-sensitive black-and-white camera are required - such as the DMK. Refractors and colour cameras typically give poor results.
