I have been doing some reading, trying to get a handle on the effects of color planetary filters by planet. I believe I understand it but wanted to get some confirmation not being up on color theory. I have not learned modern color theory but have a working understanding of Newton's outdated color chart: http://en.wikipedia.org/wiki/Image:2007_charles_blanc_etoile_des_couleurs_18... Primary and secondary opposite colors mix to produce a colorless white, black or grey. E.g. yellow and violet or red and green. Planetary color filters are transulcent. Like opaque objects, they obtain their color by absorbing colors other than their apparent color and reflecting or transmitting the apparent color. A red filter appears red because it reflects red and absorbs other colors. If a primary color is passed by a colored filter, then the opposite colors on the color wheel are suppressed. For a red filter, green and blue are reduced in brightness. This reduction in brightnesses reduces apparent color mixing to a grey hue as perceived in the eye. Paradoxically, this increases contrast of the opposite colors and the eye's ability to perceive details of features with the opposite colors that are now not completely mixed with its opposite dominent color. A red filter increases the detail seen in features that are colored blue and green. So the product inserts for let's say a Meade 25A dark Red filter states on Jupiter, that it "increases visiblity of Great Red Spot. Increases contrast of belt details." Presumably this means it passes some red but suppresses more blue and green, allowing more contrast in the blue and green details to be seen. Conversely, for a Meade 58 Green filter, the inserts describes how it on Jupiter it "increases contrast in lighter parts of the Jupiter disk by supressing red and blue toned structures. Strongly rejects blue and red tones. Use with 8" of apeture or greater." The recommendation to use larger apetures, e.g. 8 or 10 inches, depends on the percent of light that a filter transmits. High-transmission unsaturated filters can be used with smaller apetures. Low-transmission heavily-saturated filters need larger apetures to compensate for the loss of light. An analogous process occurs in modern digital astrophotography processing. A single color channel is suppressed - resulting in incomplete color mixing. So, instead of seeing featureless grey, you can see detail in the opposite partially mixed colors. Does this sound about right? How would you describe the operation of color planetary filters in terms of modern color theory with its three primary additive colors and three primary subtractive colors? See http://en.wikipedia.org/wiki/Color_theory - Thanks in advance - Kurt _______________________________________________ Sent via CSolutions - http://www.csolutions.net