If you have ever sold binoculars, you know some of the questions folks like to ask about binoculars before they buy binoculars. Some of the binocular questions are very good in terms of common sense, but some are … well, not so good. I suspect the one question that most of us binocular salespeople hate the most is, “How far can I see?” We all have our own way of answering that binocular question and, despite the temptation to supply a smart and sarcastic answer, I have always done my patient best to explain that such a binocular question is incomplete and therefore cannot be answered and that it has nothing to do with thee type of binocular in question. It cannot be answered any more for birding binoculars than it can be answered for astronomy binoculars. Okay, that response is accurate and truthful, but I learned, long ago, to quickly add more in the way of an explanation to avoid an unhappy customer.
The question needs to be completed by adding what object you are trying to see, specifically the size of the object you want to see. Object size is the crux of the question. An ant climbing a tree will not be visible in a conventional binocular at a distance of much more than tens of yards; a very large ship on a lake or ocean may be visible for miles; a galaxy in outer space is visible for millions of trillions of miles. In this line of thought, it is best to think of binocular magnification as bringing objects that much closer than they really are. A ten power binocular, then, makes objects appear ten times closer than they really are. If you are trying to see an ant on a tree at a distance of 100 yards with your 10x binocular, it will appear to be at a distance of ten yards in the binocular? Can you see an ant at a distance of ten yards without a binocular? Of course, that depends on the size of the ant; ants come in many sizes …