Patrick, I don't know any "rules of thumb", but rather, I look at the histogram to ensure that the exposure is not overexposing any areas. As long as you are not reaching saturation level on the chip, the exposures will be fine. My experience is that, generally speaking, longer exposures are better (assuming no saturation). Let the histogram guide your exposure times. That is my 2-cents worth. Cheers, Tyler _____________________________________________ -----Original Message----- From: utah-astronomy-bounces@mailman.xmission.com [mailto:utah-astronomy-bounces@mailman.xmission.com] On Behalf Of Patrick Wiggins Sent: Monday, November 12, 2007 6:48 AM To: utah astronomy listserve utah astronomy Subject: [Utah-astronomy] Color question Anyone here happen to know if there's a rule of thumb about exposures for tri-color imaging? That's to say, if an acceptable exposure for, say, Comet Holmes with the clear (luminance?) filter is 10" what would be the exposure times with the R, G and B filters? patrick _______________________________________________ Utah-Astronomy mailing list Utah-Astronomy@mailman.xmission.com http://mailman.xmission.com/cgi-bin/mailman/listinfo/utah-astronomy Visit the Photo Gallery: http://gallery.utahastronomy.com Visit the Wiki: http://www.utahastronomy.com