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Colour Filters - When to use and expected effects

Greg Walton

Object Filter Result
Moon Moon filter Reduces brightness of the Moon evenly across the spectrum
(Neutral density) Making observations easier without introducing false color
15 (Deep yellow) Enhances contrast of lunar surface
58 (Green) Like deep yellow, green will enhance contrast and detail in some lunar features
80A (Light blue) Reduces glare
Polarizer Like the neutral density filter, reduces brightness without introducing false colors
Mercury 21 (Orange) Helps to make the planet's phases clearly visible
23A (Red) Increases contrast of a planet against blue sky, aiding in daytime or bright twilight observation
25 (Deep red) Same as #23A, but deeper color
80A (Light blue) Improves view of Mercury against bright orange twilight sky
Polarizer Darkens sky background to increase contrast of planet; helpful for determining phase of Mercury



25 (Deep red) Darkens background to reduce glare; some say they also help reveal subtle cloud markings
80A (Light blue) Improves view of Venus against bright orange twilight sky
Polarizer Reduces glare without adding artificial color (especially important for viewing the planet through larger telescopes}
21 (Orange) Penetrates atmosphere to reveal reddish areas and highlight surface features such as plains and maria (best choice for small apertures)
23A (Light red) Same as #21, but deeper color
(best choice for medium and large apertures)
25 (Deep red) Same effect as #23A, but deeper color
(best choice of the three for very large apertures)
38A (Deep blue) Brings out dust storms on surface of Mars
58 (Green) Accentuates melt lines around polar caps
80A (Light blue) Accentuates polar caps and high clouds, especially near the planet's limb
Jupiter 11 (Yellow-green) Reveals fine details in cloud bands
21 (Orange) Accentuates cloud bands
56 (Light green) Accentuates reddish features such as the Red Spot
58 (Green) Same as #56, but deeper color
BOA (Light blue) Highlights details in orange and purple belts as well as white ovals
82A (Very light blue) Similar effect as #80A, though not as pronounced
Saturn 15 (Deep yellow) Helps to reveal cloud bands
21 (Orange) Similar effect as #11, but deeper color
Comets SOA (Light blue) Increases contrast of some comets' tails
Other Uses 15 (Deep yellow) Helps block ultraviolet light when doing black-and-white astrophotography
25 (Red) Reduces impact of light pollution on long-exposure black-and­white photographs taken from light-polluted areas
58 (Green) Same as #25; works well for emission nebulae
82A (Very light blue) Suppresses chromatic aberration in refractors
Minus Violet Reduces impact of light pollution without dramatically distorting color; cheaper than broadband LPR filters