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Anonymous
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How is its design different from Celestron's other SCTs from, and is it true it has better optical quality?
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jrcrilly
Refractor wienie again
Reged: 04/30/03
Posts: 22461
Loc: NE Ohio
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Hi, Francisco.
The usual setup in Celestron and Meade SCT's is a primary mirror of around F/2 with a secondary providing a multiplication of about 5, for a system focal ratio of F/10. This makes for a small, light optical tube with plenty of focal length and reasonable field flatness.
The 9.25" has a slower primary, making it necessary to place the secondary farther away. This makes the tube longer and heavier (about like the conventional 11" version) but does provide a flatter field. This is better for film or large-chip imaging.
Regarding optical quality: There's no particular reason why it should be of better optical quality although the slower primary is a little easier to figure. The C9.25 has always been a low-production model, mainly because the only bundle in which it was offered included a mount that was generally considered to be marginal for its weight. It may be that it suffered less from production line pressure and was thus more carefully assembled than the others. Now that it's offered in three different systems, two of which are very conservative for the load, it's going to be much more common.
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John C
Urban Observatory
Tele Vue Pronto
A&M/Astreya 76mm F/6 APO
TMB/LOMO 80mm F/7.5 APO
Tak FSQ-106N F/5 APO
Meade 152ED F/9 "APO"
152mm F/10 achromat
Tak CN-212 8" F/12 classical Cass/ F/4 Newt
Teeter 20" F/3.8 truss Newt w/ServoCat
LXD750, EM-200, CI-700
ST-10XME
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Rhadamantys
sage
Reged: 04/25/03
Posts: 214
Loc: France
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Quote:
Regarding optical quality: There's no particular reason why it should be of better optical quality although the slower primary is a little easier to figure.
Au contraire. With a SCT (or Mak for that matter) making the primary mirror "slower" for a given apperture has an influence on optical performances, for the better. However, the explanation (less spherochromatism = better Polychromatic Strehl ratio = Better contrast) is quite technical and therefore not especially easy to understand. This is especially useful for visual work (and cannot hurt for the rest). Of course this gain could be lost if the telescope was not well figured to begin with.
Vincent
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Vincent
"The universe is a circle whose center is everywhere and the periphery nowhere." Pascal
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Dennis
Pooh-Bah
Reged: 12/30/03
Posts: 1284
Loc: Westford, Mass
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One other small point is that the 9¼ is not Fastar capable, but the 8" and 11" are.
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Dennis
Nexstar9¼GPS
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