An optical device, such as a pair of field glasses or opera glasses, designed for simultaneous use by both eyes and consisting of two small telescopes joined with a single focusing device.

When looking through binoculars, the moon appears much bigger, yet not as big as it would seem through a telescope.

Why would you want binoculars?

You might use them for bird watching, or to identify vessels at sea.

You might watch bodies on the beach, do some sky-gazing, or watch a play or concert from the "Nosebleed seat".

Get a pair, or two. You may enjoy owning and using them.

So, what to buy?

Binoculars are classified in several ways.

First, they have an objective (front lens) diameter.

Second, they have a magnifying power-- or else a power range for binoculars that zoom. The magnifying power you might want to use depends upon what you want watch. Are you looking at birds in the yard, bodies on the beach, or stars and planets in the sky?

Third, if you wear eyeglasses while using binoculars, then an important consideration is probably the "eye relief".

What is eye relief? It's the distance from the binocular eye lens end to your eyes focusing plane.

Eyeballs vary, and eyeglasses get in the way, so, if you wear glasses, a longer eye relief is needed, and you may also look for rubber eye-cups to prevent scratching up your glasses, and get a longer eye relief on the binoculars.

If you plan to use binoculars on a bright sunny day, the objective (front lens) diameter is not critical. 7 x 35 binoculars magnify things by 7 and have 35 mm. diameter lenses on the front. This works OK in daylight, but not so well at night, where 40mm or 50mm front lenses would do better.

Higher magnifications demand larger objective lenses, so a good 15 power binocular would be more likely to have 50mm or larger front lenses.

For hand-held use, binoculars work pretty well up to about 15 or 20 power. Above 20x, using a tripod or leaning against a wall or other fixture helps to steady the image you see.

Other binocular classifications include the type of prism, the type of lenses, the grade of glass used for the prisms and lenses, and coating on the lenses (details, details).

Most of the details go to the quality of the image at the focal (eye) plane, and to the amount of light that makes it through to the eyepiece. Better binoculars have less distortion at the edge of the field, and lower light loss, due to good design and superior coatings on the lenses.

I think the best compromise is to own two, or three, pairs of "binos". Start with inexpensive 7 x 35 compact. I keep a spare pair in the car. Depending on how you use binoculars, you may decide to buy more. The second and third ones might include one slightly higher power bino, maybe a 10 or 12 power. and one high power, maybe 15 or 20x, that needs a mount, or bracing yourself against a tree or wall. Many binoculars in that range have a screw receptacle on the bottom that will mount to a camera tripod.

Beyond 20x you will want a tripod or other mount. Beyond that magnification you probably should be looking at a small mounted telescope, instead of a binocular.

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