Saturday, February 24, 2018

Binocular collimation

It has often been averred that I am a genius. Admittedly there is only one person doing this averring - viz., me, but that doesn't detract from the frequency of the observation.

Today's observation concerns fixing a pair of Swift Audubon 7x35 roof prism binoculars which were out of alignment. Nice optics for each eye provided t'other was closed, but that reduced them either to a heavy monocular with a spare attached, or attached monoculars for two viewers having Very Narrow Heads.

There are lots of internet articles on collimation and any amount of discussion but the problem is always finding how the wonky binoculars in the hand are originally aligned. Some have cunning screws hidden away to tweak the prisms. Some have eccentrically mounted objectives. Those before me turned out to have one eyepiece adjustable for focus, and the other eyepiece loose and rattly and only held in place by three dabs of glue and an eyepiece cap screwed firmly on top of them. Indeed I was a bit startled, unscrewing the wobbly one, to find the objectives were covered with flat protective glass.

Anyway the problem with a loose eyepiece is that of holding it in the right place while tightening the cap to hold it in the right place. If you point them at the communications mast on the skyline down the valley you have to levitate the lens by mystical powers inside the eyepiece cap, powers that I do not yet possess.

So I made a little wooden box with two holes in the top for the binoculars to sit on, and took the mirror off the bathroom cabinet and propped it under the holes at 45 degrees, pointed the apparatus at the horizon, and managed the job in a couple of minutes. The errant eyepiece lens obeyed Sir Isaac and sat where I prodded it while being clamped into place.

There, another averral of genius. Unf. still by the same person. Unf.ier, I didn't put dabs of glue in place, so I 'spect it will come loose rattling around under the driver's seat of the car.

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