Johnson-Cousins Filters

Developed principally by H. Johnson in the 1950's and A.W.J. Cousins in the 1970's, the Johnson-Cousins range of filters have become the defacto standard for photometry applications. During the 1990's M. Bessel developed the filters to use coloured glasses (absorption filters) to work with CCD detectors. These resulted in relatively thick filters. Over time some of the glasses used have been discontinued and issues with humidity causing degradation to the filter surface meant they had a limited lifespan. They have now evolved to make use of modern dielectric coating techniques that also provide optimum performance with the latest CCD/CMOS detectors as opposed to photomultiplier tubes which are not sensitive to the IR wavelengths like current detectors.

We offer two types of Johnson Photometry filter. A pure dielectric type from Astrodon and a hybrid dielectric / absorption type from Baader.