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Philip Levine
super member
Reged: 03/22/07
Posts: 156
Loc: near Boston, MA
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Hi Ed,
I've been following this thread, since I recently purchased a GO SS 22x85.
I have the following question, would the GO SS 15x85 generally show sharper viewing of stars/open clusters, and further out from center, than the GO SS 22x85?
thanks, Phil
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Zhumell 10" Dob (modified with degree circle and Wixey inclinometer)
26mm 2" GSO eyepiece
9mm 1.25" GSO eyepiece
13mm Nagler T6
Crayford focuser
DewBuster w/homemade heater strips
Nikon 10x50 EX binoculars
University Optics 11x80 binoculars
Fujinon 16x70 FMT SX
Surveyor Tripod w Universal Astronomics Parallelogram
member International Dark-Sky Association
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EdZ
Professor EdZ
Reged: 02/15/02
Posts: 14732
Loc: Cumberland, R I , USA42N71.4W
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Sorry, can't answer. I've never used the 15x85.
edz
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Teach a kid something today. The feeling you'll get is one of life's greatest rewards.
member#21
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pcad
Carpal Tunnel
Reged: 01/17/05
Posts: 1768
Loc: Connecticut
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Ed,
Phil's question is partly related to the differance between the low and hi power oculars available in this series of binoculars. Would comparisons between the 7x50 and the 10x50 be valid for the 85mm binoculars?
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Peter
Telescopes 25 - 318 mm
Binoculars 15 - 88 mm
Microscope 50x - 1000x
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EdZ
Professor EdZ
Reged: 02/15/02
Posts: 14732
Loc: Cumberland, R I , USA42N71.4W
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possibly not, as eyepieces act differently as f# varies, and I don't know if the f#s would be similar. Also, I don't know for certain if the eyepieces are the same, and I've never tested the 10.5x
edz
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Teach a kid something today. The feeling you'll get is one of life's greatest rewards.
member#21
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DaveL
member
Reged: 09/30/09
Posts: 12
Loc: WI, USA
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According to the Garrett website the focal ratios for this series are as follows:
50mm: f/3.7
70mm: f/4.0
85mm: f/4.7
110mm: f/4.7
It also says that the 50mm & 70mm have two element objectives in one group, whereas the 85mm and 110mm have two elements in two groups.
The ratio of the low to the high magnifications in this series are 0.70, 0.70, 0.68 and 0.71 , which, assuming the specified magnifications for the larger binoculars are rounded to the nearest integer, is certainly is consistent with the idea that the same eyepieces are used for all binos in this series.
-Dave
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pcad
Carpal Tunnel
Reged: 01/17/05
Posts: 1768
Loc: Connecticut
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Ed,
I meant the WO 7x50 compared to the series 8 10x50. I thought you had looked through a sample of both at some time.
The 10.5x is the low power version of the 15x70 series 8 binoculars. I realize you haven't looked through those.
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Peter
Telescopes 25 - 318 mm
Binoculars 15 - 88 mm
Microscope 50x - 1000x
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EdZ
Professor EdZ
Reged: 02/15/02
Posts: 14732
Loc: Cumberland, R I , USA42N71.4W
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well generally, shorter eyepieces are better corrected than longer eyepieces. BUT that's really general. There are examples where we might find shorter eyepieces not particularly any better than the longer ones.
Given the f#, the sets would be powered by 26.6mm and 18.7mm eyepieces. (The 22x85 was found to be less than 22x, and the 15x70 was found to be less than 15x, so the short eyepiece is probably more like 18.9mm, and this would agree with the actuals I've measured for that eyepiece sequence).
For ease of discussion lets call them 27mm and 19mm.
We might expect that the higher powered within the sets would be better corrected. I've never had a set in any given aperture size, but I've used the 7x50 (27mm), the 15x70 (19mm) and the 22x85 (19mm).
By actual measures, the 7x50 and the 15x70 were similarly well corrected. Both were better corrected than the 22x85. Unexpectedly, the longest eyepiece in the slowest binocular showed one of the best corrections, unless of course the WO7x50 is not of the same breed and in not using the same components. No real way to tell. Not what we would expect, but that's how they measure.
I've also used the WO22x70, which may be the best corrected of all of these.
edz
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Teach a kid something today. The feeling you'll get is one of life's greatest rewards.
member#21
Edited by EdZ (10/06/09 10:53 AM)
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