Agena 2" Color / Planetary Filter - #25 Red
Color filters can be very useful for enhancing your views of the Moon and the planets. Depending on the atmospheric conditions, the telescope being used, the observer's experience, and the planet being observed or photographed, the advantages of color filters can be anywhere from subtle to dramatic. The right filter can make all the difference between seeing several small craters in the floor of Clavius on the Moon or not; seeing five or six swirls in Jupiter's belts or not; or seeing the inner Crepe Ring of Saturn or not.
Agena's 2" color/planetary filters are manufactured from the purest optical glass and are dyed-in-the-mass (not simply "color coated") for premium performance. They thread into the barrels of virtually any 2" telescope eyepiece. Each filter cell has a male and female 2" filter thread (M48x0.75) on opposite sides, so multiple filters can be stacked to achieve selective filtration of the visual color spectrum. The clear aperture is 43mm and each filter comes in a protective plastic storage case.
The #25 Red Filter strongly blocks blue and green wavelengths, resulting in very sharply defined contrast between the blue-tinted cloud formations and the lighter-toned surface features on Jupiter. This filter is also quite useful for definition of the Martian polar ice caps and Maria. However, because of the reduced light transmission, the #25A can only be used on larger telescopes with over 8" of aperture. Try this one on Venus. Not only does it reduce the light glare, it really does some interesting things to the clouded Venusian atmosphere.
Like the light red, this filter enables observations of Mercury at twilight when the planet is near the horizon, and of Venus during daylight, reducing brightness of the blue sky to enhance surface features of the planets.