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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!).

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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.

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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!).

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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.

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

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

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

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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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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!

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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.

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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?

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