The orange filter (# 21) is useful for observing Mars' clouds and increasing contrast between light and dark areas; it may help detect dust clouds. The orange filters are used to increase contrast when observing Mercury.
1.25" Vernonscope Mounted Glass Filters feature 1" clear-aperture optical glass. Numbers are engraved on the mounting to correspond with those of Kodak Wratten series. The mountings are edge-knurled and threaded to fit the bases of BRANDON oculars and DAKIN Barlows. Vernonscope Mounted Glass Filters cut glare, provide superior contrast, improve definition and reduce eye fatigue.