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scott50
newbie
Reged: 08/18/08
Posts: 2
Loc: New York
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I have a very good Cave 12.5" f6 mirror, but I don't know its wavefront accuracy. But it give good images. I'm upgrading my secondary to an Antares
2.14". They come in various wavefronts: 1/14, 1/15, 1/18, 1/20 & 1/30 at increasing price levels. They all sound great, and I don't want to pay for something that wouldn't make a discernible difference. ANY ADVICE? Thanks.
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12.5" & 8" Dobs
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tim53
Carpal Tunnel
Reged: 12/17/04
Posts: 2300
Loc: Highland Park, CA
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First question: Why? Was the original damaged?
Total wavefront should be additive. So if the primary is 1/14th and you add a 1/14th 2ndary, the system will be 1/7th.
-Tim.
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"In the old days, before the discovery of eruptions, the lava had to be carried by hand down the mountain and thrown on the sleeping villagers. This took a lot of time." - New Yorker Cartoon, ~ 1980
Hatch Observatory details:
http://www.cloudynights.com/ubbthreads/showflat.php?Cat=0&Number=3593949&page=0&view=collapsed&sb=5&o=all&fpart=1&vc=&PHPSESSID=
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pstarr
Pooh-Bah
Reged: 09/17/04
Posts: 1389
Loc: NE Ohio
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When Cave optical sold secondaries, they were advertised as 1/10 wave. The same secondaries they used with their mirrors. That being the case, the 1/14 wave should be at least as good as the original.
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Paul
10" Home built F-6 Eq Newt. w/Zambuto mirror, built for lunar and planetary viewing.
12'x12' roll-off roof observatory
6" Home built f-6 Newt. w/Dick Wessling mirror on CG-5 Eq. mount, built for high resolution work.
4.5" Orion Starblast on Eq. mount
TV Radians 4,5,6,8,10,12,
Pentax XL 10.5mm
Pentax XW 14mm
Baader Hyperion 17mm
4&5mm UO Abbe Orthos.
3.2mm TMB planetary
TV 2.5x barlow, TV 1.8x barlow
My equipment philosophy... If it ain't broke, fix it anyway.
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sixela
Postmaster
Reged: 12/23/04
Posts: 11499
Loc: Boechout, Belgium
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Quote:
Total wavefront should be additive. So if the primary is 1/14th and you add a 1/14th 2ndary, the system will be 1/7th.
That's true for uncorrelated RMS errors. It's certainly not true of peak to valley errors, and certainly not if one is expressed on the wavefront and the other on the surface (by the way, path length difference is 1.4x smaller when you go from surface to wavefront at 45° than at 90°, another source of "apples vs. oranges").
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400mm f/4.46 self made Dobsonian on Tom Osypowski equatorial platform
Orion Starblast (114mm f/4 reflector, Alt/Az)
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