This article has been written to help you learn how to evaluate binoculars and then show you how to choose binoculars based on your budget and the purpose for which you plan to use them.
We shall be looking at how binoculars work. Understanding this will help you to understand the different factors that will affect price and the features that are available - usually these revolve around optical quality, magnification power, and portability - before moving on to look at different price categories and justifications for buying a more expensive pair depending on what they will be used for.
The overall aim is to prepare you for the task of finding the right pair of binoculars, at the right price, without compromising on features that you may require.
How Binoculars Work
Essentially, all binoculars are derived from classical telescopes, which consist, in their most basic fashion, of two lenses. The lens nearest whatever is under scrutiny (objective lens) provides an image, which can then be enlarged by the lens nearest the viewers eye (eyepiece lens), by moving it closer or further away from the objective lens.
A pair of binoculars can be seen as two such telescopes, side by side, which together produce an image which has the depth of field that we are used to, rather than just a large flat image.
Since the light has been refracted (bent) as it has been directed through the lenses, by the time the viewer sees the image it is back to front, and upside-down. To correct this, two prisms are placed inside the binoculars, between the objective and the eyepiece. It is the presence of these four prisms in the shoulders of the binoculars that give them their squat appearance.
Power, Light and Weight
The power of the optics is expressed as two numbers, such as 7 x 35. The first is the number of times magnification, and the second is the diameter of the objective lens. A larger objective lens makes sense during low light conditions, since it can capture more of the available light.
The magnification factor tells you how many times larger the object will be magnified a number of between 4 and 7 is ample for most applications. Any larger than about 9 or 10, and the natural shake of the human hand will be magnified to such an extent that the image becomes difficult to see, and a tripod will be required.
Glass also has a tendency to reflect as much as 5% of the light that arrives at its surface back towards the light source. A simple coating was devised to prevent this, by allowing more light to pass through the lens, and less to be reflected back. Since the advent of the original coating, the technique has been refined, and there are several grades of lens coating available.
The best result is achieved when multiple layers of coatings are applied, to the front and rear of the lens. Each coating is designed to provide the maximum transmission of light through the lens, and minimum reflection and diffraction, resulting in a brighter, clearer picture than with standard non-coated lens models.