Telescope Reviews: Xtra-Wide/Expanse, etc. aspheric eyepiece?

I recently saw a patent application paper for the Bushnell Xtra-Wide (and its later bretheren, I'm assuming) wherein one of the eyepiece elements was claimed to have been aspherized. This got me to wondering how to easily check for this. The method I stumbled upon is identical to that when testing for internial striae, and to be honest I was surprised at how easy the signs were to detect.

But what inspired me to even try this is the observation of the pattern within de-focused background street lights, etc., as generated by some studio cameras when a person is interviewed in front of a window facing the outside. I've seen clear signs of zonal errors which produce bullseye patterns, and my suspiscion is that an aspheric element is causing this. And no, it's not the window, because all de-focused lights show the same symmetrical pattern; a window would introduce randomness. Now to the test...

I have a pair of these eyepieces removed from the original 10X50 Xtra-Wide, and have used them in both my 11X50 right angle and modified Celestron 25X100 (now 26X). All I did was to hold the eyepiece--by itself--up to my eye and look toward a bright streetlight at night. When the pupil is at the eye point, the field is filled with a generally uniform light.

The small light source combined with high contrast against the dark surrounds allows to see the fine striations resulting from the aspheric polishing action. It has an appearance reminiscent of phonograph grooves. This indicates a period of polishing where the petal-shaped tool is centered over the lens and spun in place. This would be necessary in order to impart a non-spherical surface. But the manufacturer must have made this action rather fast and/or vigorous, and possibly with a pitch lap a bit on the hard side.

In normal use, I can't detect any significant scatter that such surface roughness would be expected to produce. It goes to show the sensitivity of this simple test.

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Home-made 11X50 right angle bino, 8.1 deg. FOV
Modified 26X100 bino, 3.5 deg. FOV
Home-made Mk II RA bino, using interchangeable objectives and eyepieces

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