Telescope Reviews: Re: My 25x100's have arrived

One test of sharpness is the splitting of doubles. My 25X100 Celestron fairly easily splits xi Cep (6"), in the middle of the "house" shape of Cepheus. I can't recall other such tests off hand. Saturn's rings should be resolvable, with gaps between them and the planet (unless the tilt is small).

As for collimation, if they feel comfortable during extended viewing, and your eyes don't seem to be out of whack immediately after you look away, they're probably OK. To get a better idea, you could do this...

Mount the bino on a tripod, aim it at a distant street light, at least 1/4 mile away, and focus the light's images on a piece of white card. Just like solar viewing. Actually, if you feel comfortable doing this (I've done it, with no problems), use the sun itself.

On the card, mark a horizontal line, with two tick marks on the line as far apart as your eye spacing (or whatever IPD you have set when doing the test). Ideally, a very distant object should project its two images exactly on the tick marks. Of course, the card must be oriented such that the horizontal line is aligned with the eyepieces.

This test becomes more sensitive as the card is moved back farther from the eyepieces. Ideally, the only kind of mis-alignment you should see is when the images project a little wider than the tick mark spacing (this means that your eyes only have to make a very easy "cross-eyed" realignment). Too much vertical displacement means that your eyes have to work like a chamaeleon's!

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Home-made 11X50 right angle bino, 8.1 deg. FOV
Modified 26X100 bino, 3.5 deg. FOV

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