SBIG Filter Set 50mm
Item No. 757-60040
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Manuf. No. SBIG CS-UBVRI
In the 1950's Harold Johnson (Yerkes and Macdonald Observatories) established three photometric bands, the U, B, and V based on the sensitivity of the photomultiplier tube that he used at the time. Later on he established red and infrared (R and I) bands using a PMT with enhanced red sensitivity. In the mid-1970's, A.W.J. Cousins and John Menzies (South African Astronomical Observatory) used different filters, that when used with a newer, better detector, would reproduce the Johnson bands. Then, in the 1980's CCD detectors were beginning to replace the photomultipliers so a new set of filters was required that, when used with the CCD's would give the same results as the older filters when used with the PMT. Bessell (Mt. Stromlo and Siding Spring Observatories in Australia) did this in 1990 (PASP, 102, 1990, 1181). It is Bessell's filter definitions that are the industry standard today when using CCD's. These professional quality, polished, AR coated, photometric filters are available in both 1.25" and 50mm sizes.
Many of the best astro images seen in Sky & Telescope and Astronomy magazine are taken with monochrome CCD cameras and color filters using RGB or LRGB combination techniques (L=luminance, R=red, G=green, B=blue, C=clear).
A luminance filter typically blocks UV and IR light, passing only the same wavelengths as the RGB filters.
A clear filter does not block UV or IR but is used for maximum signal transmission over the full range of the CCD. By taking separate images through custom filters, and combining the results to make an RGB image, the full resolution of the CCD is utilized and a great deal of latitude is preserved for image processing.