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I do think that we do see some real colour contrast in M42 - in my 16" it's very apparent that I lose the perception of redness when I lower the exit pupil, so it's dependent on the absolute surface brightness (rather than the contrast with the surroundings).

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As far as I knwow there are two origins for the red (apart for the real red).
One is the "medium lights" that are perceived as reddish when brightest lights are perceived greenish.
Another is the mechanism of color constancy (that mechanism that estimates the spectrum of the "incident" light and subtracts it from the reflected spectra seen by the cones to obtain the objects colors). This mechanism accounts for the overall lights in the scene (including presumably stars). When it is tricked it is the origin of the illusions that show red in a dominat green filed, blue in dominat yellow and produces red and other colors from nothing through a OIII filter (this is artificial but the retinex algorithm should work similarly).
Thus: if you no longer see gree because of increased magnification, you will no longer see red as compensation color. It is a fact that all colors, real and imaginary fades with reduced pupil (luminace) except fo the first mechanism.

... I think the only proof is seeing Ha.

Edited by Mauro Da Lio (12/04/07 03:56 AM)

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