The best way to describe a monocular, is to say that it is a telescope. A refracting telescope to be more exact, and the device is put to use for magnification of objects at a distance. The magnification of objects is achieved by the passing of light through lenses known as prisms. The weight and the over all size of a monocular is usually under half that of a set of binoculars, and has optical properties that are quite similar. The size of the monocular makes the device quite portable, and easy to deal with when outdoors or on the road. They also tend to be more affordable than binoculars or larger telescopes, and that helps more people afford to own such an optical device. Even though binoculars offer three dimensional perception, and the monocular offers only two dimensional perception, the ease of carry and the lower cost often offsets that point.
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One great thing about a monocular, it is a truly excellent tool for a person lacking sight in one eye, or for a person struggling with less sight in one eye than the other. And yet even some people with perfect eye sight prefer a monocular over binoculars. The monocular has a very direct optical path, and the path is fairly long. Prisms are employed to fold up the optical path making it possible for the tool to be shorter in physical length. Hunters, military people, and nature walkers all use monocular instruments to aid them when out in the bush or field. Even people that goes often to museums may employ a small monocular to assist them in viewing minute details of an exhibit that may be too far from the naked eye to closely examine. The same application would apply while at a gallery viewing an exhibition of art. Some art exhibits are so high in value as to be priceless, and such art must be viewed with a device, if to be seen in great minute detail.
A monocular is properly defined by the following two points. It’s level of magnification, and the diameter of it’s objective lens. A monocular that is detailed as being 8 x 30, would have a magnification of 8, and the diameter of the objective lens would be that of 30 millimeters. The objective lens is the monocular lens that is farthest away from the user’s naked eye. These days a common monocular would be quite compact, and have a range of 4 to 10 in the area of magnification. Zoom lenses which allow the user to adjust ranges are available but do have caveats, and zoom lenses are not normally found on the more higher end devices being sold. As for the lens, usually they are found to be in a range of 20 to 48 mm in diameter.
Where does a monocular give way to a telescope? Well, telescopes would be seen as normally having magnification range of 20 and above, with a corresponding lens diameter of 60 mm and above. The problem is that telescopes are hard to carry around in the bush, or out in the field. Binoculars are much more portable than telescopes, and yet they can get quite bulky and certainly in most cases, cannot be easily put in a pocket.
The monocular very much has it’s niche in the world of magnification, and can not be beat for comfort during an active outdoor event.