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127mm f/5.5 binocular

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#126 GlennLeDrew

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Posted 18 September 2012 - 06:04 PM

Bill,
The Richest Field Telescope is an interesting concept and subject. That such an instrument need not be large derives from the fact that at about the 11th magnitude, star numbers do not continue to increase as expected due to the combination of interstellar extinction near the band of the milky way and the fall-off in star density perpendicular to the galactic disk.

The instrument which, when operating at the largest useable exit pupil for the observer, just clearly shows stars to 11m, is The RFT. Under a dark sky, this would be an aperture of closer to 80mm, or even smaller for an experienced observer using a bino. At smaller exit pupils, or when the aperture is increased, the number of stars contained in the (same apparent) field of view decreases.

#127 Mr. Bill

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Posted 18 September 2012 - 11:42 PM

Let's see....20x80 or 29x127? Hummm...

:thinking:

#128 GlennLeDrew

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Posted 19 September 2012 - 12:38 AM

Naturally, bigger is better if one desires to see more than merely the greatest number of stars possible at a time. And so one could legitimately ask, 29X127, or 50X200, or 100X400, or....? Ever larger is better for ever smaller *objects*. My point is that at a given exit pupil and apparent field of view, a 3" will show a larger number of discrete stellar points than will a 5", or an 8", or.... Not by a large margin, and not for *every* field examined, but in the main, yes.

#129 Mr. Bill

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Posted 19 September 2012 - 09:47 AM

I wasn't disputing your statement about greatest number of stars seen in a MW field; I mentioned it because I had read somewhere the 5 inch refractor was optimal. It probably referred to fields examined without extinction coming into play. I looked through a few books on the shelf and couldn't locate the reference...I thought that Burnham or Clark had said it.

My Graemlin was ironically pointing out that maybe the greatest number of stars seen is not as important as the overall aesthetic of the field viewed.....I think the BinoBox hits a "sweet spot" in "enjoyability."

;)

#130 Gordon Rayner

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Posted 19 September 2012 - 10:39 AM

The reference you seek is a chapter by Walkden(?) in ATM II or III , depending upon the date of publication . There is a picture of Leslie Peltier there, as I recall. If you have trouble finding the article , I can find it in those books.

It was written before WW II and the large numbers of big mounted binoculars which became available after that conflict, and before the 40% gain from a binocular was discovered/ published.

There was a revision to the original article which followed subsequent stellar population in relation to magnitude research.

#131 Mr. Bill

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Posted 19 September 2012 - 01:47 PM

The reference you seek is a chapter by Walkden(?) in ATM II or III , depending upon the date of publication . There is a picture of Leslie Peltier there, as I recall. If you have trouble finding the article , I can find it in those books.

It was written before WW II and the large numbers of big mounted binoculars which became available after that conflict, and before the 40% gain from a binocular was discovered/ published.

There was a revision to the original article which followed subsequent stellar population in relation to magnitude research.


I'm sure that I didn't read the original source...the info is second sourced in one of my shelf full of astro reference books.

:question:

#132 GlennLeDrew

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Posted 19 September 2012 - 02:11 PM

Bill,
I know exactly what you're saying; for a 120mm bino of my own is on the horizon.

Gordon's memory serves him well, and I quickly looked over the chapter (the final one in the book) on the RFT in the original ATM 2. Author Walkden's original work was based on photographic magnitudes, for which the turnover in star density occurred at about 11m. The RFT aperture suggested was 2.75".

An addendum corrected things by use of then more recent data based on visual magnitudes. The star count turnover occurred at 12.4m, and so the RFT aperture was suggested as being 5".

My memory was based on the *original* study, forgetting that the magnitudes were photographic.

But for the individual, the instrument's efficiency, and depending on sky conditions, 'The' RFT is that which just shows stars at 12.4m when the maximum exit pupil is used.

Let's calculate this for myself. My out-of-town site typically allows me to just see to 6.4m naked eye. I need to gain 6 magnitudes in order to reach 12.4m. This is a brightness ratio of 2.512^6 = 251. And so my entrance pupil must be expanded so that its area is 251 times larger. That larger aperture equals the square root of 251 times 6.5, or 103mm.

Now, this is based in my two eyes being used to see those 6.4m stars. The RFT thus derived must necessarily apply to a binocular. A monocular RFT should be dimensioned so as to collect a further ~0.3m worth Of light in order to overcome the larger visual system noise imposed on a one-eyed view.

My binocular RFT is a 15.8X103.

#133 Mr. Bill

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Posted 20 September 2012 - 02:03 PM


I'm curious about whether Bill, or Glenn, or any of the other talented ATMer's on the forum, see any problem trying to take Mr Bill's design up in size to 7 or 8 inch objectives? Weight will go up, obviously. What will it take to "deliver the images" to a spot where the diagonals can be made to place the eyepieces at an appropriate IPD? Will it take an extension tube between the two diagonals in order for the final diagonal to place the eyepieces at an appropriate IPD? Will a larger binobox mount need to be a yoke type altaz mount or could could the box still "hang on one side" of a mount the way Mr Bill has done with his bino box? There are probably many more issues that I haven't thought of.


Hi Kim

As far as mounting, I would use a yoke mount for a larger binobox.

:cool:

#134 Wes James

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Posted 20 September 2012 - 02:46 PM

My binocular RFT is a 15.8X103



Would love to see a pic(s) of this!!! :cool:

#135 GlennLeDrew

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Posted 20 September 2012 - 02:53 PM

Wes,
That 'RFT for Glenn' configuration is merely the outcome of a calculation; it does not exist (at least as made by me)... I was merely illustrating how one could determine, based on their own pupil diameter and visual limiting magnitude, their personal RFT which will reveal the maximal number of stars in the FOV.

#136 Wes James

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Posted 20 September 2012 - 05:20 PM

O.K., then- I'll change that to "I'd love to see a picture of that... in my backyard"!!
:grin:
Wes

#137 Zoomit

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Posted 20 September 2012 - 07:46 PM

A monocular RFT should be dimensioned so as to collect a further ~0.3m worth Of light in order to overcome the larger visual system noise imposed on a one-eyed view.


Glenn,

Slighly off-topic but do you have a handy reference for the 0.3m gain with binocular vision? Is that after correcting for light gathering area or before?

#138 GlennLeDrew

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Posted 21 September 2012 - 01:08 AM

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!).

#139 planetmalc

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Posted 21 September 2012 - 11:11 AM

My binocular RFT is a 15.8X103.


And the OG's would be working at around f1.4 'cos you'd be using the ES 9mm eyepiece with its 120-degree AFOV.......

#140 GlennLeDrew

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Posted 21 September 2012 - 01:02 PM

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

#141 Zoomit

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Posted 21 September 2012 - 06:40 PM

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.]

#142 GamesForOne

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Posted 21 September 2012 - 11:23 PM

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.

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#143 planetmalc

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Posted 22 September 2012 - 09:58 AM

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.

#144 planetmalc

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Posted 22 September 2012 - 10:00 AM

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


Oh yes - way to go, bro!

#145 Zoomit

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Posted 22 September 2012 - 12:13 PM

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...

#146 GlennLeDrew

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Posted 22 September 2012 - 02:17 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!

#147 Mr. Bill

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Posted 22 September 2012 - 02:31 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!


:waytogo:

#148 Zoomit

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Posted 22 September 2012 - 07:14 PM

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.

#149 Mr. Bill

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Posted 22 September 2012 - 07:53 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.

:p

#150 SandyHouTex

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Posted 23 September 2012 - 07:47 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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