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Posted by Daniel Johnson on April 15, 2003 18:36:40 UTC

First, realize that the 32mm and 40mm Plossls are redundant. They show exactly the same field of view (i.e. the entire 1.25-inch barrel is the field stop) at just slightly different magnifications. So each of you can use one of those. Each should if possible get a Barlow. The least expensive Barlow worth owning is the Celestron Ultima. If you buy a cheaper Barlow you'll hate it, period. Then do the math:
40mm+Barlow = 20mm.
20mm+Barlow = 10mm, very close to 9.7
32mm+Barlow = 18, close to 15
12.4+Barlow = 6.2, close to 6.4
Be aware that the 6.4 and 9.7mm eyepieces have very little eye relief, so if one of you has to wear glasses because of astigmatism, you won't want to have those. If you wear glasses for ordinary nearsightedness or farsightedness, you can take them off and refocus the scope to compensate. Also, the 6.4mm is really too short a focal length (too high a power) for the ETX90 under most atmospheric conditions--you'll only be able to use it on those once-a-year perfect nights.
So do some thinking. Can you afford two Barlows? Or just one? Or none? Then do the math and divide as equitably as possible. Really, if you each have the ability to use focal length giving low, medium, and high power (read: 12ish, 20ish, and 32 or 40), you'll be fine.

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