Eyepiece filters are an invaluable aid in lunar and planetary observing. They reduce glare and light scattering, increase contrast through selective filtration, increase definition and resolution, reduce irradiation and lessen eye fatigue. Celestron's filters are made of high quality, solid plane parallel glass with excellent homogeneity. They're anti-reflection coated to prevent glaring and ghosting. All eyepiece filters are threaded to fit Celestron's, and most other manufacturer's, 1ΒΌ" eyepieces, and offer a full 26mm clear aperture.
Celestron color filters are mounted in black anodized aluminum cells with the Kodak Wratten Series Number individually engraved, and come available in 4 assorted kits packed in plastic cases. The cells of each filter are double-threaded, so they can be stacked (piggybacked) in various combinations. This allows you to create different color combinations and transmission characteristics, or to have the same color characteristic, but with a lower transmission. When stacking color filters, the effective transmission of the combination you create is equal to the product of the spectral transmission of each of the filters used.
The effectiveness of the filters depends on several factors, including: the aperture and focal length of the telescope, the magnification being used, and seeing conditions.
#47 Violet (3% transmission): Strongly rejects red, yellow, and green wavelengths; useful for the study of Martian polar cap regions and for the observation of occasional phenomena in the upper atmosphere of Venus. Enhances contrast between the rings of Saturn. Use only on telescopes of 8" aperture and larger.
#82A Light Blue (73% transmission): Useful on the Moon, Mars, Jupiter, and Saturn, this subtle pale blue filter enhances areas of low contrast while avoiding significant reduction of overall image brightness. A valuable filter to piggyback with other filters.
#8 Light Yellow (83% transmission): Useful in observing red and orange-colored phenomena in the belts of Jupiter and in enhancing the level of observable detail of small orange-red zonal features within the belts of the planet. Increases contrast of maria on Mars. Can result in improved resolution of dusky detail on Uranus and Neptune in instruments of 10" aperture and larger. A popular filter for the enhancement of lunar features, particularly in telescopes of 8" aperture and smaller.
Neutral Density (ND9) Filter (13% transmission): Great for the moon and observing bright planets like Venus. Since neutral density filters do not change the color of the object observed, it is excellent for use in planetary viewing. Also reduces glare, brightness, and irradiation on the Moon and planets due to the fact that it only lets 13% of the light coming through your telescope reach your eye. The filter also helps split binary stars where one of the members is significantly brighter than the other. This filter is recommended for telescopes of at least 6" in aperture.
