Re: eye pieces
- From: Margo Schulter <mschulter@xxxxxxxxxxxxxxx>
- Date: 17 Sep 2007 17:26:45 GMT
Quadibloc <jsavard@xxxxxxxxx> wrote:
Terry A Haimann wrote:
I own a 20cm sct (LX-90.) Based on that info, what eye pieces would
maxamize my investement w/o breaking the bank. If I buy them seperatly,
I could possibly afford $200 an e.p. I have been using Meade Series 4000
Super Plossls. I have a 32, 15 and a 6.4mm e.p. The 32 and 15 get the most
use.
200mm aperture, or what people used to call 8 inches. These usually
have a focal ratio of f/10.
Hi, there, Quadibloc and all.
Please let me quickly point out, as an aside, that while the decision
of whether to use oldstyle English units (inches, feet) or metrical
units is often one of style, actually 8 inches equals 203.2mm.
Thus 200mm, about 7.9 inches, is a very slightly smaller aperture.
The differences, of course, are small enough that it's often convenient
to ignore them, and call a true 8" scope "200mm," or a true 200mm scope
"8 inches."
Thus with my 200mm/1200mm Sky-Watcher Dob, we have a focal ratio of f/6,
and a 7.5mm eyepiece should yield 160X. With a 203mm/1200mm scope,
another common specification, the focal length is the same, but at a
slightly faster f/5.91. With 203mm/1219mm, 8 inches at f/6, the focal
length is a tad longer, so that a 7.5mm eyepiece yields around 162.5X.
Again, these are rather minute distinctions.
Most appreciatively,
Margo Schulter
mschulter@xxxxxxxxxx
Lat. 38.566 Long. -121.430
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