Hey all. Looking at the following link http://starizona.com/acb/ccd/projectsfaint.aspx , the page says that limiting magnitude is mostly a function of aperture.(First paragraph in the Project Ideas section) I'm wondering why that is. Doesn't skyglow increase at the same rate as the light from your target as your aperture increases? Can't you just expose for longer or take more exposures to get deeper? Other than thermal effects on the CCD, what else might limit the magnitude?