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Equipment Discussions >> Binoculars

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Zoomit
sage


Reged: 12/04/06

Loc: Tehachapi, CA
Re: 127mm f/5.5 binocular new [Re: GlennLeDrew]
      #5433337 - 09/21/12 07:40 PM

Quote:

Brandon,
The ~0..3m figure comes from the gain in signal to noise, which for two-eyed viewing equals the square root of two, or 1.414, or 41%. This is equivalent to 0.37 magnitude. But does one actually gain 0.37m in the faint star detection limit? The jury may not yet have arrived at a verdict. A gain of 0.2m would seem to be eminently realizable, and 0.3m quite possible. A matrix of variables might contribute to the actual gain.

In any event, when it comes to extended objects of low contrast, it is my sure impression that the gain is not inconsiderable, amounting to something like the 0.37m figure. The quality of the view, while numerically seeming to be small, is of no small consequence as regards the surety of detection of features near the limit of detection. How this translates to point sources has not been investigated in depth by yours truly (but it would be so easy to do!).




Thanks, Glenn. This is what I wanted to clarify. You're saying that going from a 5" monocular to a 5" binocular is equal to ~0.3m gain, or about equal to the effect from the increased light gathering area. In this case increasing the aperture from a 5" monocular (20 in^2) to either two 5" scopes or a single 7" scope (both 40in^2) yields an additional 0.3m.

[Edit: This is in error. A 7" mono yields 0.7m over a 5" mono.]

Edited by Zoomit (09/22/12 01:32 PM)


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GamesForOne
professor emeritus


Reged: 09/29/09

Loc: Knoxville, TN
Re: 127mm f/5.5 binocular new [Re: Zoomit]
      #5433714 - 09/22/12 12:23 AM

Quote:


Thanks, Glenn. This is what I wanted to clarify. You're saying that going from a 5" monocular to a 5" binocular is equal to ~0.3m gain, or about equal to the effect from the increased light gathering area. In this case increasing the aperture from a 5" monocular (20 in^2) to either two 5" scopes or a single 7" scope (both 40in^2) yields an additional 0.3m.




Actually, there has been much discussion about this in past threads. The sqrt(2) multiplier should be applied to the area of one objective to get the equivalent area of a single objective. You do not simply add the areas of both bino objectives as binocular summation is not equivalent to a simple addition of the two areas.

When you apply a sqrt(2) increase to the area of one objective, the equivalent diameter multiplier works out to be 2^(1/4). Therefore, two 5" scopes using binocular summation are the theoretical equivalent of a 5" * 2^(1/4) = 5.9" single objective.

See the past discussion here.

---
Michael Mc


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planetmalc
sage


Reged: 10/21/09

Re: 127mm f/5.5 binocular new [Re: Zoomit]
      #5434204 - 09/22/12 10:58 AM

Quote:

Quote:

Brandon,
The ~0..3m figure comes from the gain in signal to noise, which for two-eyed viewing equals the square root of two, or 1.414, or 41%. This is equivalent to 0.37 magnitude. But does one actually gain 0.37m in the faint star detection limit? The jury may not yet have arrived at a verdict. A gain of 0.2m would seem to be eminently realizable, and 0.3m quite possible. A matrix of variables might contribute to the actual gain.

In any event, when it comes to extended objects of low contrast, it is my sure impression that the gain is not inconsiderable, amounting to something like the 0.37m figure. The quality of the view, while numerically seeming to be small, is of no small consequence as regards the surety of detection of features near the limit of detection. How this translates to point sources has not been investigated in depth by yours truly (but it would be so easy to do!).




Thanks, Glenn. This is what I wanted to clarify. You're saying that going from a 5" monocular to a 5" binocular is equal to ~0.3m gain, or about equal to the effect from the increased light gathering area. In this case increasing the aperture from a 5" monocular (20 in^2) to either two 5" scopes or a single 7" scope (both 40in^2) yields an additional 0.3m.




We do it for the sheer pleasure of using 2 eyes; the 0.3 mag gain is just a bonus.


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planetmalc
sage


Reged: 10/21/09

Re: 127mm f/5.5 binocular new [Re: GlennLeDrew]
      #5434206 - 09/22/12 11:00 AM

Quote:

Is that a dig at my predilection, my proclivity, my penchant for ultra-wide fields? ;grin:




Oh yes - way to go, bro!


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Zoomit
sage


Reged: 12/04/06

Loc: Tehachapi, CA
Re: 127mm f/5.5 binocular new [Re: planetmalc]
      #5434437 - 09/22/12 01:13 PM

Quote:

We do it for the sheer pleasure of using 2 eyes; the 0.3 mag gain is just a bonus.




Your comment is actually at the heart of my inquiry. It goes beyond the summation discussion. I completely understand the "shear pleasure" of using 2 eyes and I'd like to quantity that effect. From an equivalent light gathering perspective, which correlates with cost, using two eyes yields about a 0.4m loss over an equal area monocular. [Using the examples above, a 5.9" scope gives up 0.4m to a 7" scope.]

What is it that motivates us to ignore the additional cost of using two eyes? Is there a way to quantify this? Probably should start a new thread...


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GlennLeDrew
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Reged: 06/18/08

Loc: Ottawa, Ontario, Canada
Re: 127mm f/5.5 binocular new [Re: Zoomit]
      #5434638 - 09/22/12 03:17 PM

Brandon,
Binocular viewing incurrs a *cost*? Quite the contrary; it affords a *gain*. And the equivalence is: a 5" bino about equals a 5.9" singleton.

But to me this 'aperture equivalence' is academic, and belongs only in the sphere of the theoretical. In the real world, the 5" bino is a 5" aperture instrument which allows the most efficient use of our two eyes. If anything, when bandying about this aperture equivalence thing, it's more realistic to state that a 5" telescope is actually closer to a 4.2" binocular! Squinting with one eye is an unnecessary handicap to be avoided. That's how binoculars should be promoted!


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Mr. Bill
Postmaster
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Reged: 02/09/05

Loc: Northeastern Cal
Re: 127mm f/5.5 binocular new [Re: GlennLeDrew]
      #5434649 - 09/22/12 03:31 PM

Quote:

Brandon,
Binocular viewing incurrs a *cost*? Quite the contrary; it affords a *gain*. And the equivalence is: a 5" bino about equals a 5.9" singleton.

But to me this 'aperture equivalence' is academic, and belongs only in the sphere of the theoretical. In the real world, the 5" bino is a 5" aperture instrument which allows the most efficient use of our two eyes. If anything, when bandying about this aperture equivalence thing, it's more realistic to state that a 5" telescope is actually closer to a 4.2" binocular! Squinting with one eye is an unnecessary handicap to be avoided. That's how binoculars should be promoted!






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Zoomit
sage


Reged: 12/04/06

Loc: Tehachapi, CA
Re: 127mm f/5.5 binocular new [Re: GlennLeDrew]
      #5435032 - 09/22/12 08:14 PM

Quote:

Brandon,
Binocular viewing incurrs a *cost*? Quite the contrary; it affords a *gain*.

//cut//

Squinting with one eye is an unnecessary handicap to be avoided. That's how binoculars should be promoted!




Oh come on, there's huge premium for a binocular view, as we're all aware. To most people, that incremental pleasure from a binocular view cannot justify the significant additional expense and complexity. That's why most telescopes, even those intended to be only visual instruments, remain monocular.

Even in refractor vs newt vs SCT debates, there are quantitative comparison data and arguments. I've tried to logically justify a binocular view but the argument always seems to boil down to: two eyes are better than one.

Which is where I started when I posed my original question (and with apologies to Mr. Bill, the OP, for taking the thread down this path). I was hoping Glenn had a quantitative metric that captured the "sheer pleasure" of a binocular view, beyond the straightforward summation equations.


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Mr. Bill
Postmaster
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Reged: 02/09/05

Loc: Northeastern Cal
Re: 127mm f/5.5 binocular new [Re: Zoomit]
      #5435086 - 09/22/12 08:53 PM

As the OP, it seems appropriate that a new thread be started on the topic of "cost vs. benefit of binocular vision compared with monocular vision."

Certainly this discussion has gone astray from the construction and use of my BinoBox.



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RodgerHouTex
Pooh-Bah
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Reged: 06/02/09

Loc: Houston, Texas, USA
Re: 127mm f/5.5 binocular new [Re: Mr. Bill]
      #5435660 - 09/23/12 08:47 AM

Okay, back to your binobox. How is the chromatic aberration? I'm pretty sensitive to that with a telescope, but don't notice it much in my binos. Is it because of the lower magnifications involved?

I'm toying with the idea of using a pair of the 6" Istar f/5 objectives to make a binobox. I'm also concerned about field curvature in an f/5 objective. How is the field curvature in yours?

Thanks,


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JKoelman
professor emeritus


Reged: 05/16/11

Loc: Bangalore, India
Re: 127mm f/5.5 binocular new [Re: Mr. Bill]
      #5435747 - 09/23/12 09:44 AM

Quote:

My amazement is that someone (as far as I know) hasn't done this design commercially as it is very practicable and avoids a lot of the problems of the porro prism design.




These guys seem to be commercializing a 3 mirror design: http://www.astro-mechanik.de/doppelfernrohre.htm


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Rich V.
Post Laureate
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Reged: 01/02/05

Loc: Lake Tahoe area, Nevada, USA
Re: 127mm f/5.5 binocular new [Re: JKoelman]
      #5435945 - 09/23/12 11:43 AM

Yes, that was also the approach used in the Astromeccanica/Borg binoscope reviewed by Milt Wilcox eight years ago.

Rich


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Mr. Bill
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Reged: 02/09/05

Loc: Northeastern Cal
Re: 127mm f/5.5 binocular new [Re: RodgerHouTex]
      #5435958 - 09/23/12 11:48 AM Attachment (26 downloads)

Quote:

Okay, back to your binobox. How is the chromatic aberration? I'm pretty sensitive to that with a telescope, but don't notice it much in my binos. Is it because of the lower magnifications involved?

I'm toying with the idea of using a pair of the 6" Istar f/5 objectives to make a binobox. I'm also concerned about field curvature in an f/5 objective. How is the field curvature in yours?




Good question...I have both the Istar 6 inch f/5 lens set (in a MonoBox design I did last year) and of course the 5 inch f/5.5 lens sets.

Not overly impressed with CA and field curvature in the 6 inch....the 5 inch lens sets are much better in both parameters. Stars are pinpoint using Panoptics out to 90% of edge of field in 5 inch.

Actually, my Celestron (Synta) 6 inch f/5 shows a much better image than the Istar 6 inch, so the Istar's shortcomings go beyond the laws of physics.

However, for magnifications under 75x, the 6 inch f/5 objectives would do a good job for scanning MW fields.


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Mr. Bill
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Reged: 02/09/05

Loc: Northeastern Cal
Re: 127mm f/5.5 binocular new [Re: JKoelman]
      #5435978 - 09/23/12 12:00 PM

Looks to me they just stack 2 inch diagonals. I have to wonder about vignetting even at f/7.

My design uses a 3.1 inch mirror as the first element and by careful raytracing gives over 70% edge of field illumination and of course full effective aperture.

My comment about this design not being commercially available really refered to a fully integrated binocular....not just hanging diagonals on two telescopes.

Edited by Mr. Bill (09/23/12 12:45 PM)


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GlennLeDrew
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Reged: 06/18/08

Loc: Ottawa, Ontario, Canada
Re: 127mm f/5.5 binocular new [Re: Mr. Bill]
      #5436518 - 09/23/12 04:50 PM

I wondered also about the vignetting and potential aperture loss incurred by having to push the focuser drawtube farther inward along the optical path when additional diagonals are attached at the back end...

A system designed from the ground up will be better in these respects.


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RodgerHouTex
Pooh-Bah
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Reged: 06/02/09

Loc: Houston, Texas, USA
Re: 127mm f/5.5 binocular new [Re: Mr. Bill]
      #5437869 - 09/24/12 11:07 AM

Thanks Mr. Bill. I think you may have saved me from a very expensive mistake with the 6" Istar.

And the 6" f/5 Celestron (Synta) you're talking about is the Newtonian right?


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Mr. Bill
Postmaster
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Reged: 02/09/05

Loc: Northeastern Cal
Re: 127mm f/5.5 binocular new [Re: RodgerHouTex]
      #5437908 - 09/24/12 11:33 AM Attachment (40 downloads)

No....that would be comparing apples and oranges.

It's a two element achromat just like the Istar.

Here's a picture of the two comparing coatings.

Not meaning to discourage you....for binoculars I think the Istar 6 inch f/5 lens sets would be fine....I chose to use the 5 inch f/5.5 lens set for mine because of size/weight considerations.


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RodgerHouTex
Pooh-Bah
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Reged: 06/02/09

Loc: Houston, Texas, USA
Re: 127mm f/5.5 binocular new [Re: Mr. Bill]
      #5437960 - 09/24/12 11:59 AM

Okay then I'm wondering where are the Celestron/Synta lenses available. When I did a search, I just came up with the 6" f/5 Newt.

Thanks,


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Rich V.
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Reged: 01/02/05

Loc: Lake Tahoe area, Nevada, USA
Re: 127mm f/5.5 binocular new [Re: RodgerHouTex]
      #5437988 - 09/24/12 12:15 PM

Rodger, here's the 6" f5 refractor:

Celestron Omni XLT 6" refractor

Don't see it available as an OTA only, though.

Rich


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Mr. Bill
Postmaster
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Reged: 02/09/05

Loc: Northeastern Cal
Re: 127mm f/5.5 binocular new [Re: RodgerHouTex]
      #5437993 - 09/24/12 12:17 PM

I think you would have to buy two OTAs. Might make an interesting project using their tubes.

You could shorten the tubes to accomodate the relay mirror.

Frankly, I would go with the Istars...just remember that no matter what, short focus achromats will never give you good high magnification images.

The most I use on the Celestron is a 10mm Ethos which yields 75x. After that, the image degrades rapidly.

Just noticed from Celestron ad copy that the lens is aspheric....that would account for superior spherical aberration correction.


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