Times Kevin_Times Kevin 9/18/18 10:51 AM Page 1 ofthe adjustments has been inadvertently reset. In doing so, you will maintain the dioptric difference between your eyes regardless ofthe distance to the target—500 feet or 5,000,000,000 miles. (Only 2 to 3% ofthe population have the same setting in each eye.) Spatial accommodation Spatial accommodation is a collimation (alignment) issue that, more often than not, originates with the binocular but which can be caused by the binocular’s IPD (interpupillary distance) to be misplaced relative to the separation ofthe user’s eyes. For example, just placing a binocular to the eyes is inadequate unless positioned in such a way that the binocular’s exit pupil is placed precisely in front ofthe pupils ofthe observer’s eyes. If the observer has an IPD of 69 millimeters and the binocular’s IPD is set to match, all is well. If not, the observer must use some degree of eye-straining spatial accommodating, even if the binocular is well collimated. The Internet is replete with articles telling observers how they can “easily” correct misalignment by tweaking a few through-the-body/prism-tilt screws, with most such instructions omitting other alignment conventions and the repairs often needed to allow any of those conventions to work. There are, however, stipulations of which the exuberant screw-tweaker needs to be aware. IF only one side ofthe binocular is misaligned, IF that side is the one adjusted, IF the error is small, IF the individual’s physiological accommodation is adequate, and IF the distance to the desired target is far enough this—conditional alignment—may be enough to make the instrument perform well or even excellently. Even so, while that is adequate for some users, it leaves others, who didn’t have all those IFs in their favor, frustrated with a less than crisp image. In addition, without specific knowledge, the same procedure can push the binocular ever farther out of alignment and can, in some cases, damage the instrument. And although rarely, if ever, seen in print, understanding spatial accommodation is critical to getting the best view from the binocular. So, if you find that your binocular gives you a double—or even an uncomfortable—image you should consider that the binocular may be misaligned or you don’t have the telescopes spaced properly for your eyes. In order to find out, bring the binocular to your eyes and seek the best view of a target at least a mile away. A streetlamp will work fine. Then slowly move the instru- 54 www.timespub.tc
The Mourning Dove epitomizes “protection” as she keeps careful watch over her chicks. The bird is so-named for its melancholy call.