Binoculars Abound!

Jack Kramer

If a poll were taken, I bet we'd find that a very large percentage of amateur astronomers own binoculars. Perhaps they pre-date a first telescope purchase, or maybe they were obtained more recently. Binoculars are useful for seeing objects in the sky as the first step in locating them in a telescope. But they're also useful as a stand-alone, wide-field observing tool. The sight of star fields using both eyes gives the feel of a universe in 3-D!

While the planets are disappointing in binoculars, quite a few of the brighter deep sky objects are within their grasp. In particular, finding the Messier objects in binoculars is a fun project. (The Astronomical League has Messier observing lists keyed to the various sizes of binoculars.) They're also great for following the day-to-day movements of bright comets. Sometimes binoculars actually provide a better overall view than a telescope. One such case is when the moon or a planet passes near or in front of a large star cluster. Remember when Jupiter played tag with the Beehive Cluster? Finally, they're handy for those times when you want to have a look at the night sky but don't feel like hauling out your telescope.

For astronomical purposes, probably the smallest useful size is the common 7x50 binoculars. The "7" refers to the magnification and "50" refers to the diameter of the objective lenses in millimeters. Smaller "pocket size" binoculars are limited due to their inability to grasp enough light to view fainter objects. As you'd expect, the view in progressively larger binoculars becomes more spectacular. But handholding the larger, and therefore heavier, ones for any length of time becomes progressively more difficult. Binoculars with higher magnification are also harder to use because the field of view becomes narrower and you fight the "jiggles". The various makes and models of binoculars weigh in differently; however, 9x60s may be about the largest hand-holdable size for a lengthy observing stint.

Another type of binocular has the "zoom" feature that allows you to change magnification by simply turning a thumb lever. But according to Phil Harrington, author of Touring the Universe Through Binoculars, "To perform this feat, zoom models require far more complex optical systems than fixed power glasses. More optical elements increase the risk for imperfections and inferior performance. Additionally, image brightness suffers terribly at the high end of their magnification range, causing faint objects to vanish."

It's a lot easier to prop your elbows on something when looking at a terrestrial target with binoculars than when viewing an object high in the sky. If you want to carefully examine a celestial object, then you should have a mounting for any size binoculars, be it just a camera tripod or one specially designed for use with binoculars. Phil Harrington advises: "...the secret to seeing challenging objects through any binoculars is to put them on a mount of some sort. That's an absolute must, since handholding binoculars will never let you get their full potential. That goes for image-stabilized binoculars, as well. Sure, the internal gyroscopic control will steady the view, but if you are really intent on pushing binoculars to their limit, you will undoubtedly have to refer back and forth to charts, just as you would with a telescope. If you're supporting the binoculars by hand, you'll have to relocate the field every time you set them down to look at the chart, then star-hop from there. That strikes me as very inconvenient."

A common support designed specifically for binoculars is the "parallelogram" mount. The name derives from the design of the arm that supports the binoculars. This type of mount raises the binoculars high enough so you don't have to scrunch down to look through them, as is sometimes necessary with a regular camera tripod. It also accommodates people of various heights.

One of the newer products is the "Sky Window", which allows you to mount binoculars so they are facing downward and you're looking at the sky reflected in a front-surface mirror. This is the most comfortable method - sort of like looking through a microscope. Users report no distortion in the images and that they quickly become acclimated to moving around the sky. The makers of Sky Window also sell a laser pointer that can be attached to it and used for aiming at an area of the sky. The only negative is that you have introduced an additional optical element (the mirror) which can cause a scattering of light that would prove detrimental mostly to faint objects.

It was only a couple of years ago that I got binoculars suitable for astronomical purposes. Now I wonder why I waited so long!

Published in the November 2003 issue of the NightTimes