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 #12 Yellow Filter increases the contrast of blue and green areas on Mars, thus darkening the Maria, oases and canal markings, while lightening the orange-hued desert regions. It sharpens boundaries of yellow dust clouds and the blue clouds in the Martian atmosphere and is thus a favorite for viewing the red planet.
The yellow filter contrasts strongly with blue-colored features on Jupiter and Saturn, thus enhancing red and orange features of the belts and the zones. It darkens atmospheric currents containing low-hue blue tones and may be used for studies of the polar regions on these planets. Like the other yellow-tinged filters, it improves detail in larger telescopes in Uranus and Neptune while with Venus it reveals otherwise low-contrast features. This filter also enhances definition in comet tails and is useful in increasing the contrast of lunar features in telescopes of 6" aperture and larger.