Times of the Islands Winter 2019/20

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Presents the "soul of the Turks & Caicos Islands" with in-depth features about local people, culture, history, environment, businesses, resorts, restaurants and activities.

Times Kevin_Times Kevin 9/18/18 10:51 AM Page 1

of the adjustments has been inadvertently reset. In doing

so, you will maintain the dioptric difference between your

eyes regardless of the distance to the target—500 feet

or 5,000,000,000 miles. (Only 2 to 3% of the 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

of the 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 of the

pupils of the 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

of the 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

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