Binoculars or binocular telescopes, are really two identical symmetrical telescopes mounted together. Because they point in the same direction, they allow the viewer to see a far greater distance than with the naked eye. A binocular has a big advantage over single telescopes as you can see through both eyes and they are easier to hold steadily with two hands.

The Optics

The objective lens diameter generally determines how much light is allowed while the magnification will display the ratio of the focal lengths. An example is 8 X 35 (eight times magnification and 35 mm objective diameter) or 7 X 50 (seven times magnification and 50 mm objective diameter). In these two examples, the first one has a higher magnification ( 8 over 7) but allows less light (35 mm is smaller than 50 mm) than the second one. If you are requiring binoculars for low light use, buy the biggest objective diameter.

Lens Construction and Coatings

Unfortunately, in any optical instrument used for images (e.g. a telescope, camera, microscope, etc.) light is often reflected and distributed into the view. This can reduce contrast. Reflection can be reduced by adding coating to the optics. Some of the newest techniques are phase-corrected prism and dielectric prism coatings.

Binoculars designed from the Porro prism design are generally brighter than a roof prism design but newer technologies are reducing the differences (the Porro prism binoculars still have the highest value at a lower price).

Choosing binoculars

Roof-prism models are generally lighter and smaller than Porro models, but you will usually pay more. If the binoculars are sealed and filled with nitrogen gas, they will not cloud with condensation.

Manufacturers Include

Bushnell Performance Optics
Canon
Docter Optik
Eschenbach Optik
Fujinon
Kowa
Leica
Leupold & Stevens, Inc.
Minolta
Miyauchi
Nikon
Olympus
Optolyth
Pentax
Russian Military Binoculars
Sicong
Steiner
Swarovski Optik
Vixen
Vortex Optics
WDtian
Yunnan State
Zeiss