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Secrets of Deep-Sky Observing
Capturing Color
Deep-sky objects disappoint beginners not only by lacking obvious detail, but also by lacking the brilliant colors recorded in photographs.
In order to show us color, a deep-sky object must have a high enough surface brightness to stimulate the retina's cone cells — and the list of deep-sky objects this bright is short. The brightest parts of Great Orion Nebula (M42) qualify, as do some small but high-surface-brightness planetary nebulae. The ability to see color in dim objects varies greatly from person to person, and surprises may occur.
Averted vision is not the way to look for color. The cones are thickest in the fovea, so stare right at your object. In this case, the lowest useful power should work best. A large telescope aperture is especially advantageous for those who seek to see color in deep-sky objects.
