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Equipment Discussions >> Binoviewers

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GlennLeDrew
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Reged: 06/18/08

Loc: Ottawa, Ontario, Canada
Re: Deep-sky binoviewer - contrast vs light loss new [Re: Astrojensen]
      #6303728 - 01/10/14 09:07 AM

Thomas,
Methinks thou didst read too swiftly. I did not imply a halving of area. I stated that a halving of aperture is a dimming by 1.5 magnitudes. If we have a 12" scope, what aperture is half that? Why, 6" of course. And so the light collecting area is 1/4, and the magnitude equivalent is 1.5.


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Astrojensen
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Re: Deep-sky binoviewer - contrast vs light loss new [Re: GlennLeDrew]
      #6304290 - 01/10/14 01:57 PM

Eeerhm - guess I am still a little confused about it... But I think I get that it was just an example of how a smaller scope affects what's being seen and it had no *direct* relation to the binoviewer discussion?


Clear skies!
Thomas, Denmark


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GlennLeDrew
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Re: Deep-sky binoviewer - contrast vs light loss new [Re: Astrojensen]
      #6304425 - 01/10/14 02:57 PM

Yes, it's more fundamental 'background' info on how use a telescope on dim objects, with OR without a BV attached. I was stressing that smaller apertures are fine when appropriate objects are viewed.

The number of comments which have it that smaller apertures are not suitable for BV use due to the dimming puzzle me. A BV-equipped scope is just like a true binocular. Both instruments are defined by the same laws if optics. If a Binocular can be used down to quite small apertures, so can a BV. The very same brightness offset as exists between some huge true bino and a same-aperture BV/scope applies for all other aperture regimes.

If we accept that a 10" true bino and, say, an 11" scope w/BV are equivalent in terms of image brightness, then it's the case that a 3" bino and a 3.3" scope w/BV are equivalent. Or 1" and 1.1".


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Astrojensen
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Re: Deep-sky binoviewer - contrast vs light loss new [Re: GlennLeDrew]
      #6304474 - 01/10/14 03:23 PM

Quote:

I was stressing that smaller apertures are fine when appropriate objects are viewed.




Absolutely. Viewing 11th mag galaxies in a 60mm is the same as observing 16th mag galaxies in a 24". You just got fewer to choose from... And a lot fewer objects that do appear very bright in the eyepiece.

Quote:

The number of comments which have it that smaller apertures are not suitable for BV use due to the dimming puzzle me. A BV-equipped scope is just like a true binocular. Both instruments are defined by the same laws if optics. If a Binocular can be used down to quite small apertures, so can a BV. The very same brightness offset as exists between some huge true bino and a same-aperture BV/scope applies for all other aperture regimes.




Totally agree, but I offer an explanation: People don't know how to make the binoviewer work at low magnification. This dims the view uncomfortably. The situation is made worse by the fact that many large scopes are often very fast f/ratio (big dobs certainly are) and thus have a much better starting point, if a barlow is needed to reach focus, since the final f/ratio is still not all that slow.

Quote:

If we accept that a 10" true bino and, say, an 11" scope w/BV are equivalent in terms of image brightness, then it's the case that a 3" bino and a 3.3" scope w/BV are equivalent. Or 1" and 1.1".




A scope with binoviewer needs to be 1.4x the aperture of a true binocular telescope to show the same brightness in the eyepiece. But it will be far more compact and easy to manage. It will not be able to go to as low magnifications as the true binocular telescope or show as wide a true field.

A 14" with binoviewer is the same as a true 10" binoscope; a 100mm is the same as a 70mm; a 11.2" is the equivalent of an 8" binocular, etc.


Clear skies!
Thomas, Denmark


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GlennLeDrew
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Re: Deep-sky binoviewer - contrast vs light loss new [Re: Astrojensen]
      #6304533 - 01/10/14 04:05 PM

Thomas,
If one were viewing through a BV with just one eye, then the 1.414 ratio (and its reciprocal, 0.707) on aperture would certainly apply. Integrating two signals, however, regains some of that loss, which when applied to the two dimmed images gets you back up in equivalent aperture an additional 1.189 times in aperture. And so for a 10" with BV, the one-eyed equivalent aperture is 7.07", and with two eyes on the case it becomes 7.707 * 1.189 = 9.16".


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Astrojensen
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Re: Deep-sky binoviewer - contrast vs light loss new [Re: GlennLeDrew]
      #6304650 - 01/10/14 05:16 PM

Hi Glenn

Exactly. A binoscope with 70mm objectives has the same performance on detection of threshold deep-sky objects as a 82mm telescope with a single eyepiece. And a 100mm scope with a binoviewer has the same performance as a 82mm scope with a single eyepiece, when it comes to detection of threshold deep-sky objects, because each eye sees the same amount of light as with a 70mm objective.

Thus, as I said: A 70mm binoscope has the same visual limiting magnitude as a 100mm scope (1.4x the aperture) with a binoviewer. They meet halfway, so to speak. The 70mm binoscope performs better than its aperture would suggest and the 100mm with bino performs a little worse.

To match the visual performance of a 10" binoscope, with a single scope with a binoviewer, one would need a 14", because splitting the light from the 14" in two gives each eye the equivalent amount of light a 10" delivers.


Clear skies!
Thomas, Denmark


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Hothersale
sage


Reged: 10/13/09

Loc: Victoria, BC
Re: Deep-sky binoviewer - contrast vs light loss new [Re: Astrojensen]
      #6304890 - 01/10/14 07:49 PM

I agree, Thomas. It is only necessary to factor in the summation effect when comparing bino-viewing to mono-viewing. Comparing binoculars to binoviewers, brightness is strictly a function of total aperture, making a 10" binocular and a 14" telescope roughly the same. (Of course, the 14" telescope would still have a resolution advantage over the 10" binoculars.)

It occurs to me that talking about the "summation effect" is a backward way of thinking about things. We observe the world with two eyes 99% of the time, but in astronomy we have accepted as normal the brightness deficit that our brains experience when observing with only one eye. In reality, mono-viewing offers a dimmed view of the universe.


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Chopin
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Re: Deep-sky binoviewer - contrast vs light loss new [Re: Hothersale]
      #6305612 - 01/11/14 08:02 AM

Quote:

It occurs to me that talking about the "summation effect" is a backward way of thinking about things. We observe the world with two eyes 99% of the time, but in astronomy we have accepted as normal the brightness deficit that our brains experience when observing with only one eye. In reality, mono-viewing offers a dimmed view of the universe.




I have to say, this is the first time I've actually heard or read this statement in such context. It's simple and brilliant. I concur completely.


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GlennLeDrew
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Re: Deep-sky binoviewer - contrast vs light loss new [Re: Chopin]
      #6305632 - 01/11/14 08:21 AM

That's what I've been 'preaching' for a while now; with a monoscope you're hobbling yourself, and a bino is really the natural instrument. I've essentially eschewed mono viewing, preferring to stick to even the smaller true binos rather than do the cyclopean squint. I've cone to really dislike the one-eyed view of anything. It so obviously lacks the 'presence' that Su desire.

To see (and hear this) in action, try this while watching the tube some time. Spend a little while with one eye and one ear covered then open them up again. The increased signal to noise offered by both your paired eyes and ears should be notable. This will be felt as a more 'definite' presence. Particularly if the screen and sound are on the dim side.


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Arizona-Ken
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Reged: 08/31/08

Loc: Scottsdale, Arizona
Re: Deep-sky binoviewer - contrast vs light loss new [Re: GlennLeDrew]
      #6305708 - 01/11/14 09:10 AM

"... cyclopean squint ..."

I like it. And, "cyclopean" is an actual word!

I am a big user of binoviewers, and do all of my deep sky work with a C11 and some EarthWins. As posted in this forum by many others numerous times, the more comfortable, natural use of two eyes makes it easier to spend more time with the view, actually allowing one to observe more.

And our brain, actually using information from two eyes as mother nature has us wired to do, gets more information from the view. However, although we can calculate all manner of optics, this improvement of using two eyes instead of one can probably not be quantified.

Arizona Ken


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