Binoculars are widely used by amateur astronomers, bird watchers and hunters. Modern binoculars have a wide field of view, which makes them useful for comets and supernova seeking. The major market, however, is amongst those, who mostly prefer the lighter, but more expensive roof-prism models.
There are a lot of different binoculars today. Binoculars are not frisbees, and choosing the one you need can really be a problem for a beginner. This article will provide some useful information as for what binocular will suit you best and how it can be chosen.
Ideally a pair of binoculars produces two uniformly sharp images, each of a perfect quality. There have to be no errors of geometry or colour-correction and no internal reflections. The two images must be identical (apart from the slightly different viewpoint), with no differences in size, orientation, aberrations, etc. Real binoculars differ more or less from the ideal.
Choosing a binocular, make sure it is accurately aligned, comfortable to use, and robust. Roof-prism models are lighter and more compact for a given size. Nevertheless, they are more expensive than equivalent Porro models.
Choose the magnification and objective diameter according to your requirements. Remember that the higher magnification exaggerates shaking when hand-held, and that larger objective lenses increase the weight and size. If you need a binocular for a general-purpose use, try an 8x40 combination. A 7x50 is brighter for a night use. If you would like to view fainter objects for an astronomical use, you should prefer larger objective diameters, as they have better light-gathering power. If you need more compact binoculars, you can use smaller objectives at some loss of performance and increase in price. Zoom binoculars are in principle a good idea, but they do not perform very well.
You may come across some "focus-free" binoculars (and cameras). This is a perfect example of marketing departments making a virtue of necessity. Such binoculars have a depth of field from a relatively large closest distance to infinity. They perform exactly the same as focusing models of the same optical quality (or lack of it), focused on the middle distance.
Another trick: binoculars of the same production and model may vary from unit to unit. This is less so for the more highly priced models from quality manufacturers. By the same token many cheaper types of generally 'so-so' quality, but basically of a nice design, may have a few really great units.
What binoculars are the best? Choosing binoculars, it is best to try them out in person. It is you and only you, who will decide how much magnification you can hand, hold steadily and how much weight is comfortable for you to carry. You should feel how binoculars fit in your hands and how they work with your eyeglasses.
Some popular binocular manufacturers as of 2005: European brands: Leica GmbH; Swarovski Optik; Zeiss GmbH, etc.; Japanese brands: Canon Co., Nikon Co., Pentax Co., Minolta Co., etc.; Chinese brands: Sicong, WDtian, Yunnan State optics; American brands: Bushnell Performance Optics, Leupold & Stevens, Inc., Vortex Optics, etc.