On telescopes of 6" aperture and larger the #23A does approximately the same functions as the #21 filter, but with stronger contrast and enhancement of marginally defined bluegreen surface detail. Useful primarily on Jupiter, Saturn, and Mars. Increases contrast between Mercury and bright blue sky during daylight observations or during twilight. This filter has a 25% transmission.
Large 26mm in clear aperture
Manufactured from the purest crown optical glass
Dyed-in-the-mass (not color coated)
Each filter glass is anti-reflection coated on both sides and is mounted in a machined aluminum cell with the Wratten No. of the filter marked on the side of the cell.
Filters may be piggybacked, or stacked, to achieve selective filtration of the visual color spectrum.
