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 #56 Green Filter is marvelous for increasing the contrast in Mars' polar ice caps as well as yellow-tinted Martian dust storms. It also does a reasonable job of increasing the contrast of cloud patterns on Venus. This filter strongly rejects red and blue wavelengths and increases the contrast of these regions in Jupiter's atmosphere as well as in the cloud belts. It can also enhance the white portions of Saturn's cloud belts and polar regions. The green filter is useful for enhancing lunar detail. It also reduces blue-sky brightness here on Earth. This filter should be used only on large (over 8") scopes.