Orion Green #58 1.25" Eyepiece Filter #3392
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About color filters...
Planetary (Color) Filters
Backyard observers also utilize an array of color eyepiece filters to glean subtle features on the planets. Earth's atmosphere is in constant fluctuation; turbulent air currents blur fine surface detail on solar system objects, like planets, viewed through a telescope. Faint, contrasting areas blend together due to irradiation - distortion of the boundaries between light and dark areas. Using color eyepiece filters can help reduce such distortion.
A color filter zeros in on a narrow region of the spectrum, reducing the scattering of interfering wavelengths. Because many planets have a characteristic color (e.g., Mars is reddish), a filter can dramatically increase detail by reducing the predominant hues and uncovering hidden contrast and surface markings. That's why the Red Planet is most effectively enhanced with a green filter. Each color eyepiece filter passes its characteristic color of light while blocking complementary colors. For example, green objects will appear bright (pale) through a green filter, and dark through a blue or red filter. Red features will appear bright through a red eyepiece filter and dark through a green or blue eyepiece filter.
Telescope eyepiece filters thread into the barrel of an eyepiece. Usually the aluminum cell holding the filter is threaded such that two or more can be "stacked," to achieve simultaneous filtering of more than one color.
Color filters go by their "Wratten" numbers. Here is a rundown of the color eyepiece filters that are useful for enhancing detail on each planet and some other objects.
#25 Red will make the planet's disk stand out against a blue sky, permitting daytime or twilight viewing. Mercury is usually best observed just after sunset, when the sky is awash in orange light, so employ #21 Orange with high magnifications to see the planet's phases.
No matter what telescope aperture you use, Venus's excessive brightness usually causes a very "overexposed," roiling image. With a #47 Violet filter, or stacked #58 Green and #80A Medium Blue filters, you'll reduce the severe twinkling for a better view of the fascinating changing phases.
#25 Red passes the predominant reflections of surface plains and maria, and #21 Orange is good for reducing the intense glare to enhance detail and mottling. The polar caps stand out with #15 Deep Yellow and #80A Medium Blue; examine the melt lines with #58 Green.
This great planet reveals its cloud bands, loops, festoons, ovals, and Red Spot with #80A, #58, and #21. Go from seeing only two bands without a filter to seven or more with a filter! Try stacking filters to reduce the heavy glare.
Many subtle details are improved by #15 Deep Yellow. See the difference in brightness of the extremes of the rings with #25, #58, or #80A. The #15 filter also helps sharpen Saturn's image in photographs, improving the resolution of the Cassini division.
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