If you buy 20x80 binoculars for astronomy, you are making things difficult for yourself. When you have full night vision, your pupil will dilate to around 7mm. An exit pupil that size is perfect for best light transmission through your eyes. 20x80 gives you an exit pupil of 4mm (80/20=4). I bought a pair of Celestron 8x56 which are fully multicoated. A 7mm exit pupil and fully multicoating is perfect for light transmission which is obviously what we want in astronomy and a good reason why I'm not keen on high powered binoculars. If they are used during the day, it won't matter too much about the exit pupil unless it's rediculoulsly small. If people are going to spend lots of money buying high powered binoculars with small exit pupils for astronomy, they are better off buying a telescope instead.