Aperture and focal length both affect image brightness. The former collects more or less light, and the later spreads it over more or less area (magnification). The10” offers broader field of view, lower magnification or spreading of nearby points of light, with its 1600mm focal length. The 14”s 3554mm f.l., a 2.2x difference in magnification is not 2.2 times dimmer because it has a 2x larger (area) mirror. Thus the 14 inch image (above) appears barely brighter than the 10” image at the same magnification.