5-6 mm is pretty typical for adults. Of course, binoculars are largely intended for daytime use, and the makers don't want the objectives to be any larger than necessary (because of added weight and cost), so many binoculars are designed with a 5mm exit pupil. Astronomical binoculars are usually designed for a 7mm exit pupil, optimized for somewhat younger users with fully dilated pupils.neufer wrote:Why have a 5mm exit pupil on binoculars
if 5mm is the maximum eye dilation at night?
Indeed, and this does provide some benefit in sensitivity, even though the brightness is unchanged. It's one of the main reasons for using higher magnifications with dim objects.Twice the retina area means twice the number of illuminated rods & cones for each eye.
Which is, in fact, barely noticeable.4 air-glass surfaces => Transmission = (0.96)4 = 85%
Not that I know of. A one inch aperture (especially at 5X) makes seeing the Sombrero very easy. While a larger aperture supports more magnification, which means more of the retina illuminated, that isn't necessary at all for simple detection of the object.Galileo had telescopes with effective apertures larger than an inch?