Robert Ellis said:
93,000,000 miles is, astronomically speaking, quite close. Infinity is not the best term but it is the one used, I suppose because in relation to terrestrial observing the far end of the focus is of little concern. There are plenty of binoculars that don't have a far end long enough to get crisp focus on stars.
Hello, all,
New guy here; I have enjoyed using binoculars for some 45 years now. I was hesitant to join yet another forum, but what the heck! I have gleaned some good info from this group. I've seen Robert come over to the CN Binocular Asto. forum and it is good to see folks realize that binoculars have a place in the world of astronomy as well as terrestrial use. Why waste half your life?? ;^)
In regards to binoculars and their ability to focus at infinity, I have never seen a binocular that couldn't. For most glasses, infinity focus extends from several hundred yards to the stars; it makes no difference after a point. If anyone who has normal vision cannot see stars in sharp focus they have a defective binocular, IMO. Of course, what is considered "sharp" varies between binoculars, the smaller the point of light the better.
I have been using binoculars for astronomy for over 30 years now. What I have noticed over the years is that in the quest for closer focusing distances, manufacturers have been taking away some of the "-" diopter range in favor of the "+" side. My old Nikon Es have a range of +10/ -5 diopters which would accomodate many who choose not to wear eyeglasses while viewing. My newer E2 glasses have quite a bit less "-" adjustment but have really close focus instead. The same applies to my newer roof glasses.
Folks like me who have hyperopia (farsightedness) have no problem focusing at infinity without eyeglasses; all you have to do is focus closer and infinity snaps right into focus. Those of you with myopia however, have very little latitude to focus without eyeglasses; that part of the focus range "beyond" infinity has been whittled away.
This is why many glasses with individual focusing eyepieces are favored by astronomers. These typically have an equal range +/- of infinity. Once focused you just leave them; there is no flexing eyepiece bridge to cause focus to move in and out. The down side is that they don't focus as close as most CF glasses and focusing is certainly not speedy.
Anyway, sorry to make such a verbose first post; you have a great forum here.
Rich V