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GlennLeDrew
professor emeritus
Reged: 06/18/08
Posts: 633
Loc: Ottawa, Ontario, Canada
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Re: Some tid-bits obout the 2.3x40 Owl eyes
06/26/08 06:43 PM
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KerryR,
It's not the aperture that imposes a limitation to the use of narrow bandpass filters, but exit pupil. The Owl Eye has a rear eye lens clear aperture of >8mm, allowing you to use your eye's full pupil diameter. Therefore the really narrow filters are perfectly OK!
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I did some more in-depth examination with my Owl Eyes last night. As already noted, with the rear eyepiece cover threaded off, I can get my eyes sufficiently close to see the full field. For example, The full length of the Big Dipper fits in with no trouble, and Scorpius comes really close to squeezing in. Another nice view was provided by the "kite" figure of Bootes and Corona Borealis, again, in the field all at once.
Comparing the apparent field (which necessarily has a fuzzy edge, being a Galilean system) against a 5x21 having a 60 degree afov, I'd say it's pretty close. According to the numbers, 2.3X times 28 degrees = 64 degrees. And it might just be that large.
And as already pointed out, when the eye is centered properly, the stars are beautifully sharp out to a surprisingly large off-axis distance. I reaffirmed the important of centration of the eye, and indeed, it is folly trying to assess star sharpness well off-axis by looking away from the field center because of the now incorrect eye placement. When looking on-axis, the stars are sensibly sharp to the "edge" of the field.
I also verified that a Galilean design does NOT make a good auxilliary telescope to place behind another instrument's eyepiece. The portion of the field seen is VERY small!
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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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