Telescope Reviews: William Optic binos

I agree Glenn,

I did perform this test exactly as described. This morning I did so more accurately, on two primary targets and on many stars. Looking backwards thru the BV, no ocs.

First, single stars. Every single star I looked as was double.

Then the moon. The thin cresent along the bottom of the moon was doubled such that there was a thin black line between images of the cresent.

Then, in order to accurately measure, I observed a single star, but also with theta1-theta2 Taurus in the field of view for comparison. t1-t2 Taurus is approximately a 6 arcmin pair, an easy naked eye pair. The BV shows all single stars as doubles. It was easy to compare a single star seen as double image to that of the pair t1-t2, a double of known separation. Double image stars observed in the same fov as t1-t2 looked to be about 2/3rds as wide as t1-t2. So this provides me with a measure of the reverse viewed error at about 3.5 to 4 arcminutes.

Yet, during observing in normal mode with eyepieces thru a telescope at 110x power, this binoviewer has less than 3 arcseconds of error. I also viewed at 200x and essentially saw no miscollimation error. FWIW, 4 arcmin of error would be a devastating error at 110x. For comparison, 4 arcmin miscollimation error would be the approx allowable error for a 12x to 15x binocular and experience tells me that my eyes cannot accept the allowable errors, but only about half allowable error is agreeable to me. At 110x it would be magnified almost 10x that of a binocular.

My binoviewer shows nearly 4 arcminutes of error in reverse, yet shows less than 3 arcseconds of error in use. That's a factor of 240 versus 3 or 80:1. Even if I've overestimated the backwards view error and it is only 3 arcminutes, that's still 60:1. That could potentially mean that you could see 15 arcminutes of error backwards (half a moon width) yet have only 15 arcseconds of error in use (acceptable probably up to about 150x).

This reverse test may not translate directly to miscollimation error. It ignores the fact that there could be conditional alignment in the eyepiece barrels compensating for small errors in the prisms. In fact, as I mentioned above, one BV supplier publishes instructions to perform collimation at the eyepiece collets and to not touch the prisms. I will note however, IIRC I have used an external adjustment screw on a Stellervue BV3.

But my conclusion is this, I don't see this reverse view as a reliable test of collimation. I would still recommend to anyone that they observe thru the BV at normal powers, preferably observe a double of known separation, and actually measure any miscollimation that might be present in actual use. A good double to measure gross error is nu Draco. it's 62 arcseconds, essentially 1 arcmin. There are many other closer doubles that can be used.

t1-t2 Taurus 337 arcsec or 5.6 arcmin
e1 e2 Lyra 207”
56 And 190”
39 Cnc 150”
nu Draco 62"
16 Cyg 39”
Alya, theta Serpens, 22"
100 herc 14"
Mesartim, gamma Aries, 7.8"
95 herc 6.3"

edz

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