(Looking Beyond the Obvious)
by William J. Cook
Image stabilized binoculars have added a new dimension to navigation, water-borne safety, and for those who would admit it, viewing pleasure. Thus it is no wonder they have been gaining rapidly in popularity.
Without a doubt the stabilizing feature dramatically increases a binocular’s usefulness. Still, there is much more to seeing than that which can be obtained through a jitter-free image, and when planning to buy an Image Stabilized instrument, one should also consider: Aperture, Magnification, Field of View, and just what can be expected by way of stabilization.
Pride of ownership can cloud one’s mind to the realities of what to expect from any of these high-tech devices. But, careful consideration will show the needs of a day-sailor puttering around Puget Sound is quite different from someone prone to long voyages or spending a lot of time cruising off the coast of Canada.
The apertures for the most popular IS (image stabilized) binoculars fall between 30 and 50 millimeters. With every square inch of objective lens (the large front lens) gathering the light of nine fully dilated eyes, it’s easy to see that the larger the objective—the brighter the image at a given magnification. I say “given” because just as increasing aperture increases image brightness, so, too, will increasing magnification work to diminish it.
Another factor of choice is Magnification. Binocular users in general have a tendency to believe that magnification—“power”—is the most important aspect any optical aid. Nothing, however, could be further from the truth. High-tech or not, IS binoculars don’t have magical powers; they only transmit the light that strikes their objective lenses. That means an increase in magnification will result in a dimmer—somewhat harder to see—image.
Field of View:
As interplay between aperture and magnification, Field of View is also something to be determined by the user.
It is for the sailor to determine which is more important. Is it a bright, clear image in a field of view wide enough to easily find his target? Or will he sacrifice field of view for the ability to identify those things once he has found them through using a higher power? There is no right or wrong answer, it’s merely a question of personal preference. It’s not within the scope of this article to be a primer in the binocular basics. But, each mariner should know deciding on the right IS binocular for his or her needs requires more consideration than factors concerning stabile images!
The figure shows a sign created to help the mariner choose his or her IS binocular at Captain’s Nautical Supplies in Seattle.
The white dot in the “bull’s eye” shows the size of the bundle of light rays coming from several popular IS instruments. They’re shown relative to each other, the trusty traditional 7×50 binocular, and a person’s pupil on a day of subdued brightness.
From this graphic, it is also easy to see that the size of an instrument’s rear eyelens has little to do with the amount of light that passes through the instrument!
Finally, IS technology is great for correcting rapid, short-term vibrations—body tremors, engine vibration, wind gusts, and the like—they do relatively little when it comes to constant, long-duration motions such as pitch and roll. But then, just handling the rapid vibrations for which they were designed can make dealing with wave action much easier to live with.