Baader 1.25 inch Baader U-Filter (ZWL 350nm) not for photometry
With the Baader Planetarium U filter amateurs can now record cloud structures on Venus. The Baader Venus Filter enables amateurs to successfully image in the deep UV, a spectral region normally inaccessible.
The latest coating technologies permit the Baader Venus Ultraviolet Filter to transmit from 300nm to 400nm, with a peak transmission of 80%! The filter completely blocks the rest of the region from 200nm to 1500nm, through the use of a complex 20 layer dielectric coating stack, on top of a special UG-11 substrate. Up till now, Amateur efforts typically relied upon deep violet colored filters, or combinations with simpler interference filters, which do not provide the high transmission and efficient rejection outside the important spectral region from 320nm to 390nm. Given the poor transmissions of many optics in the UV and the lower sensitivity of some CCDs to this wavelength, high filter efficiency and complete rejection at longer wavelengths becomes paramount to recording good contrast at reasonable exposures. The same high optical quality and features as the other Baader filters ensures the highest contrast and sharpest images possible.
Interestingly, the solar Calcium K-Line is also within the pass band of this filter. This opens up the exciting possibility for recording flare structures on the solar disk or edges. The Baader U Filter has become the choice of UV imagers exploring the UV world of landscape, floral, and even forensic imaging.