Patrick, Thanks for the notes. The method I outlined only applies to targets at opposition - which for asteroids can be determined in real time using Warner's MPO Canopus Lightcurve group. http://www.minorplanetobserver.com/Misc/EphemerisGenerator.htm But I forgot to ask the obvious first question: Is the asteroid in the photo at opposition? If it was not, then the method discussed upthread is not directly applicable. I have not run the specific computation to find the distance limit for a diurnal parallax measurement. It probably would reach the inner asteroid belt using amateur equipment, but not 1 A.U. Warner's Asteroid Ephemeris Generator lists the following asteroid as coming to opposition on July 30 - 1004 Belopolskya, mag 14.4, but it is at a distance 3.8 A.U. - Clear Skies - Kurt