Posted by Richard Miles at 22:27 on 2013 Dec 06
As you can see from the comprehensive responses of Martin and Grant that you certainly have the capacity to reach 20th magnitude using a 10" aperture but that there are quite a few things they mention to get the best out of your scope.Very good seeing can have a remarkable effect on going faint provided that you have an accurate focus. When doing a long time-series of a mover with the aim of tracking and stacking to go as deep as possible, you may have to refocus the instrument several times especially during the first 2-3 hours of use (i.e. when the temperature is dropping) to ensure the stars are reasonably pinpoint. So it’s often worth checking the turbulence in the upper atmosphere by looking at say the 300 mbar level pressure chart forecast, e.g. at:http://www.wunderground.com/wundermap/?zoom=4&rad=0&wxsn=0&svr=0&cams=0&sat=0&riv=0&mm=1&mm.mdl=GFS&mm.type=SURPRE&mm.hour=0&mm.opa=100&mm.clk=0&hur=0&fire=0&tor=0&ndfd=0&pix=0&dir=0&ads=0&tfk=0&fodors=0&ski=0&ls=0&rad2=0Select ‘Model data’then click on the ‘Tools’ symbolthen under ‘Map type’ select 300 mbthen move the ‘Forecast’ slider to the time and date you intend to observethe chart you obtain is colour coded: anything purple is good or very good seeing; anything green or yellow is poor seeingNo point in trying to go really faint if the weather and seeing is against you, despite it being a clear sky.Richard