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.
GSO filters are made of high quality, solid plane parallel glass with excellent homogeneity. They are anti-reflection coated to prevent glaring and ghosting.
All eyepiece filters are threaded to fit GSO and most other manufacturers 1.25" eyepieces and offer a full 26mm clear aperture. The color filter detail as follow:
#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.
#11 Yellow-Green (78% transmission): Contrasts well with the red and blue characteristics of surface features on Jupiter and Saturn. Darkens the maria visible on Mars, and clarifies the Cassini division in Saturns rings.
#12 Yellow (74% transmission): Contrasts strongly with blue-colored features on Jupiter and Saturn, while enhancing red and orange features. Lightens red-orange features on Mars, while reducing or blocking the transmission, and thereby increasing the contrast, of blue-green areas. Useful in increasing the contrast of lunar features in telescopes 6" aperture and larger.
#21 Orange (46% transmission): Reduces or blocks transmission of blue-green wavelengths. Use on Jupiter and Saturn to enhance detail in the belts and polar regions. Sharpens boundaries between yellow-orange areas and blue-green regions on Mars, resulting in a darkening of edge-detail in the maria.
#23A Light Red (25% transmission): 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 blue-green surface detail. Useful primarily on Jupiter, Saturn, and Mars. Increases contrast between Mercury and bright blue sky during daylight observations or during twilight.
#25 Red (14% transmission): The #25A filter strongly blocks the transmission of blue and blue-green wavelengths, resulting in very sharply defined contrast between, for example, blue-tinted cloud formations on Jupiter and the lighter-toned features of the disc. Also useful for the delineation of the Martian polar ice caps and maria. Because of its relatively low total light transmission the #25A filter should be employed on telescopes of 8" aperture and larger.
#38A Dark Blue (17% transmission): A popular filter for the study of Jupiters disc, owing to the filters strong rejection of orange and red wavelengths. Increases contrast between the reddish belt structures and enhances detail of the Red Spot. Also useful for the study of isolated phenomena, such as dust storms, on Mars, as well as the belt structure of Saturn. Increases contrast of subtle cloud markings on Venus.
#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.
#56 Light Green (53% transmission): Use on telescopes 8" aperture and larger to reject blue- and red-toned structures on the surface of Jupiter and thereby increase their contrast relative to lighter parts of the disc. Also use for the enhancement of Saturn's cloud belts and polar regions. Strongly increases contrast of Mars' polar ice caps, and increases contrast of atmospheric phenomena on Venus.
#58A Green (24% transmission): Excellent for the observation of Martian polar ice caps as well as yellow-tinted dust storms on the Martian surface. Increases contrast of the red and blue regions in Jupiters atmosphere as well as in the cloud belts. Also useful for enhancing lunar detail.
#80A Blue (30% transmission): A popular filter for the study of Jupiter and Saturn. Enhances contrast of rilles and festoons in Jupiter's cloud belts, as well as details of the Red Spot. Brings out detail in Saturn's belts and polar phenomena. Very useful as a contrast-enhancing lunar filter.
#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.
**When ordering "Any combination Filters", PLEASE specify the Filter #'s & the Color in the COMMENT SECTION when ordering.
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