Night Vision Binoculars
Amateur astronomers study the heavens as a hobby relying mostly, if not exclusively, on optical tools, since they do not have access to hi-tech equipment that measures infrared or ultraviolet radiations. They use either a telescope or binocular depending on the kind of heavenly image they want to study.
The most common celestial bodies observed by amateur astronomers are the moon, stars and star clusters, planets, galaxies, comets, nebulae, and meteor showers. Since these are better seen at night, their optical equipment must be suited for low-light conditions. Telescopes are often used, but for certain purposes and under certain conditions, binoculars are a better choice.
One of the main advantages of binoculars over telescopes is their wider field of view (FOV). When studying star clusters or widely dispersed meteor showers, you will want an FOV wider than what most telescopes can offer. Another advantage of the binoculars is their ease of use and portability.
You will want a binocular that can pick up images even in surroundings with very low-light. The three factors that can give your binocular this capability are:
- Prism type. Porro prisms, named after their inventor, Ignazio Porro, are deemed better than roof prisms in terms of gathering light. The type of glass used for the prism is also important. BAK-4 type is often preferred over BK-7 as it offers superior quality.
- Objective lens diameter. With a bigger lens diameter more light will be able to pass into the optical tubel, thus providing a clearer image. You may need a minimum of 50 mm for good nighttime observations.
- Exit pupil. If you hold your binoculars at arm’s length, you will see a circle of light in the eyepiece. That is the exit pupil. Its diameter is determined by dividing the objective lens diameter by the magnification. This opening controls the amount of light coming out of the binoculars. If it is larger than the pupil of your eyes, some of the light will fall on your iris, and thus will remain undetected. On the other hand, if it is smaller, you will perceive the image as dim because only a portion of your pupil will receive light. Therefore, since most astronomical observations occur at night, and since your pupils dilate when it is dark, it is advisable to choose a binocular with a wide exit pupil. Indeed, an exit pupil of at least 7 mm is recommended for nighttime viewing. You can get this measurement from a 7×50 mm binocular.
Most amateur astronomers consider a 7x magnification sufficient for their hobby. However, magnifications of up to 30x coupled with a 60 mm objective lens are also available for binoculars. This increase, however, comes at the price of portability and handiness.
Binoculars and telescopes are not rivals when it comes to observing the skies. They have their own roles to play and they actually complement each other. If you can afford to purchase only one of these fine optical tools, God bless you. That is a very difficult choice.
