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fred1871
professor emeritus


Reged: 03/22/09

Loc: Australia
Re: General Double Star Observing Equipment Question new [Re: WRAK]
      #6148994 - 10/20/13 07:43 PM

Wilfried, I would quibble slightly about BU 67 being "about a limit unequal double" for 140mm. Agreed, it will need good seeing conditions; and for the inexperienced double star observer will be more difficult than for the experienced; but somewhat more difficult pairs are possible for 140mm.

I'd agree that for 140mm it's a reasonable "light test" (as in "not heavy"), as the observers of 100 years ago would have said.

BU 67, incidentally, was discovered with a 6-inch refractor by SW Burnham ; at the time it was a little closer than at present, so 140mm (5.5-inches) these days makes it comparable to the discovery situation.


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Bill Boublitz
super member


Reged: 05/04/13

Re: General Double Star Observing Equipment Question [Re: fred1871]
      #6149038 - 10/20/13 08:10 PM

Indeed. And I'm fairly certain most modern 6" refractors would put Burnham's to shame. (Though, who wouldn't want to add it to their collection?)

Thank you Bruce, for some of the most sane advice I've read on these pages.

Clear skies...


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WRAK
scholastic sledgehammer


Reged: 02/18/12

Re: General Double Star Observing Equipment Question new [Re: Bill Boublitz]
      #6149300 - 10/21/13 05:37 AM

Bill and Fred - I don't know what you expect from a 140mm Achro bargain buy. A +10mag companion is already some challenge and my RoT says 152mm for BU67 so 140mm would be a reasonable good performance. With good seeing you can certainly be successful a smaller aperture (my own best value so far is 120mm) and from Bill I expect (without irony) a positive report with 100mm.
Wilfried
PS to Fred regarding Royce DK: I am curious if old wizard Bruce has good arguments for his strong opinion. Bob Royce informed me that the blanks for my scope already exist and that he will begin working on my scope end of this year. So I expect delivery not too early at begin of next year. I am rather optimistic regarding performance for resolution of doubles as I expect near perfect mirrors from Bob Royce and with a CO of 0.25 I know meanwhile due to my CO experiments that I can expect zero CO performance - I will see if reality meets my expectations


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fred1871
professor emeritus


Reged: 03/22/09

Loc: Australia
Re: General Double Star Observing Equipment Question new [Re: WRAK]
      #6149379 - 10/21/13 08:05 AM

Wilfried, Dave Lee may have picked up a telescope cheaply, but it doesn't have to mean it's a poor telescope. The Vixen 140 is not the usual short-focus achro; it's a Petzval design, the OG has a longer focal ratio than the final f/5.7; maybe around twice that.

Eddgie did a review of the model years ago, here on CN; his review and other information resulted in me deciding to get one. Initially I had a faulty scope; astigmatism. It went back to Vixen, who replaced the faulty element, resulting in a very fine achro refractor. I expect I've been lucky and now have an above-average version of the Vixen 140. But Eddgie reported on using powers up to 370x or so.

An example of one of the doubles of fairly large delta-m and 10th mag secondary I've seen with the 140: BU 1190 in Orion, mags 6.95 and 9.81 at 1.4" - seen double at 285x. Another, A 146 in Virgo, mags 7.31 and 10.77 at 1.7", just double at 160x, better seen at 230x.

So that's the story behind the 'scope I've used for the reports here of doubles. It gives very fine images. Chromatic aberration? - of course. Goes with being achro, but it turned out a much better scope than I'd expected. But, of course, samples vary; so Dave will discover the quality of his copy by using it.

And, Wilfried, it's interesting that you have a Royce DK on order; I'd thought you were getting a Tak Mewlon. I'm looking at Royce DKs also, due to their excellent reputation. Like you, I'm looking for something more specialised than my C9.25 for double stars; highest grade optics, smaller CO, better thermal qualities. Hence Royce is a possible.


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astroneil
Pooh-Bah
*****

Reged: 07/28/09

Loc: res publica caledoniae
Re: General Double Star Observing Equipment Question new [Re: Bill Boublitz]
      #6149382 - 10/21/13 08:08 AM

Quote:

Indeed. And I'm fairly certain most modern 6" refractors would put Burnham's to shame. (Though, who wouldn't want to add it to their collection?)



Clear skies...




Hiya

http://neilenglish.net/s-w-burnham-a-life-behind-the-eyepiece/


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WRAK
scholastic sledgehammer


Reged: 02/18/12

Re: General Double Star Observing Equipment Question new [Re: astroneil]
      #6149708 - 10/21/13 11:44 AM

Fred, Mewlon has gone back due to image shift issue.
Wilfried


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Dave Lee
sage


Reged: 02/14/13

Loc: Pinehurst, NC USA
Re: General Double Star Observing Equipment Question new [Re: Dave Lee]
      #6150499 - 10/21/13 08:00 PM

Quote:

FWIW I have just bought (used) a Vixen 140mm NA140SS 'Neo achromat'. See this thread, http://tinyurl.com/ll6fhmu , in this forum for more information.

This is kind of a poor man's Televue in a way. It has an f11'ish (don't know for sure) achromatic objective and a focal reducer in the rear (built in) that brings the optical train down to f5.7. From a visual optical performance perspective it has many of the characteristics of a longer fl achromat but in a smaller package.

I honest did not chose this scope because I felt it was the best choice for me. I have become convinced that 'the best choice' for me is right now indeterminate. I wouldn't know it if I saw it (or in the case of a 175mm AP Starfire couldn't afford it). And this (used) scope was a very good price and I think that I can recover my investment if/when I decide to experiment.

Scope is (literally) in the mail.

dave




A short first light review can be found here (Refractor forum).

http://www.cloudynights.com/ubbthreads/showflat.php?Cat=0&Number=6150495&...

dave


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Ed Wiley
scholastic sledgehammer


Reged: 05/18/05

Loc: Kansas, USA
Re: General Double Star Observing Equipment Question new [Re: Dave Lee]
      #6150587 - 10/21/13 09:00 PM

About Royce DKs. I have the first of the 8 in. scopes. Excellent optics and easy to collimate. I wouldn't know about 'refractor-like' views, but I can capture double images down down to 1" with a video camera. That takes good optics.

Ed


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fred1871
professor emeritus


Reged: 03/22/09

Loc: Australia
Re: General Double Star Observing Equipment Question new [Re: Ed Wiley]
      #6150840 - 10/21/13 11:26 PM

Ed, thanks for your very positive comments about Royce DKs. "Easy to collimate" is a definite plus as well. I'd recently asked Anthony Wesley about his experience with Royce mirrors, which he uses for his outstanding planetary imaging, and he was also very positive about Royce optical quality. Looks like a good option for doubles.

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drollere
Pooh-Bah
*****

Reged: 02/02/10

Loc: sebastopol, california
Re: General Double Star Observing Equipment Question new [Re: fred1871]
      #6176086 - 11/04/13 07:10 PM

(PM sent.)

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