A monocular is a miniature, low powered telescope or spotting scope which you hold in your hand like a binocular but use with one eye like a telescope. A monocular shares characteristics with both binoculars and spotting scopes, but is much smaller than either. Size, then, is really what a monocular is all about. Some monoculars are no larger than your thumb or thicker than a good ink pen and any monocular will slip easily into a pocket or a purse. When a spotting scope or a binocular, even a compact, is too large to take along, there is always a monocular. There is no excuse for leaving home without your monocular.
A good time to consider buying a monocular is anytime you need to keep things small and just need to take a peek. Is that a rock or a deer out in that field? Pull a monocular out of your pocket and take a look. What does that sign across the shopping center say? Pull a monocular out of your purse or pocket and take a look. A monocular can also do double duty as a magnifier. Some actually have a very close focus, but turn any magnifier over, hold it over an object and you have a magnifier.