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12" Apochromat Refracting Bino Scope

John

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Peter Drew

Peter Drew

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Posted

I have a 12" F3.5 APO binocular telescope, they don't need to cost a  major lottery win, provided you use mirrors :grin: . I can vouch for the impressive views that can be obtained though you still can't get the wide field of smaller instruments. My lowest magnification avoiding secondary shadowing or oversize exit pupil is 50x. I would love to compare them with the refracting model, hopefully there would be a big difference. There is in the cost!  :eek:

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nicks90

nicks90

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Posted

exactly that - total aperture!

it also tends to be shorter in tube length for a given mirror surface area, provide bigger FoV and lower magnification.

eg, 12" mirror surface area is 706 cm2 = 1412 cm2 for a binocular. At F3.5 the tube length will be 105cm long.

to have a single mirror with the same surface area, it would need to be a 17" mirror and tube length would be 150cm long! 

tube length / focal length will also affect minimum magnification as well before exit pupil gets too big, so its a way of having a whopping mirror area without resorting to high minimum mags and reduced field of view!

But then you have the problems of aligning the tubes...

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RT65CB-SWL

RT65CB-SWL

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OK, as a comparative newbie, let me ask the daft question. What is the advantage of a binocular arrangement with two OTAs, over a single OTA with a bino eyepiece? Apart from total aperture of course.

Ian

I would have thought 3D...

I find comets appear better through my binoculars than through my 'scopes.

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ollypenrice

ollypenrice

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Posted

exactly that - total aperture!

it also tends to be shorter in tube length for a given mirror surface area, provide bigger FoV and lower magnification.

eg, 12" mirror surface area is 706 cm2 = 1412 cm2 for a binocular. At F3.5 the tube length will be 105cm long.

to have a single mirror with the same surface area, it would need to be a 17" mirror and tube length would be 150cm long! 

tube length / focal length will also affect minimum magnification as well before exit pupil gets too big, so its a way of having a whopping mirror area without resorting to high minimum mags and reduced field of view!

But then you have the problems of aligning the tubes...

I don't think the advantage is the total aperture. This is a very complex question and I'm not sure what the answer is. I don't know if anyone does. For instance, if you close one eye, what happens to the view? It doesn't get dimmer. You lose a small amount of resolution, particularly if you have a weaker eye, as most people do. You also lose distance perception, but at the distance to the stars there can be no possible benefit, strictly optically, from a separation of a few inches. It took over a hundred years of positional astronomy before it was possible to measure the parallax created by two astronomical units during an Earth orbit.

I think the advantage is psychological/physiological. That isn't to say it's illusory, not at all. But I think that for some people using both eyes allows their eye-brain to do better than it does with one eye closed. 

How do you look through this beast? On an equatorial the two EPs are going to be some contorted angles. I would have thought a tracking Alt-Az would make a lot more sense?

I tired a binocular pair of C11s on an equatorial and my osteopath made a fortune out of me!   :grin:

Olly

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Peter Drew

Peter Drew

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It's a popular misconception that a binocular benefits from a summation of the two apertures. Unfortunately it doesn't work like that for some neurological reason, as Olly says, closing one eye doesn't make things darker. What a binocular does do is produce two signals to the brain instead of one signal and one noise. This the brain likes and rewards you with a double stacked image which appears somewhat brighter and more detailed, you also get an illusion of 3D in proportion to the separation of the two objective centre spacings. A binoviewer provides some of these benefits but the usual beamsplitter arrangement results in substantial light loss although this is much mitigated by the two signals syndrome.  :smiley:

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Stu_2011

Stu_2011

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So if anyone out there is planning a trip to Hong Kong - best to bring an umbrella. Something tells me it's going to rain for 40 days and nights now.....

:eek: ,

Dave

I used to go to HK on a regular basis. Fantastic city with fantastic people but I must admit it wouldn't be my first choice location for housing a scope like this. The pollution, both light and smog is quite significant at times.

Hong Kong Island and Kowloon are particularly bad for light pollution. It might be better in parts of the New Territories but then the smog rolls in from Shenzhen.....

Stuart

Sent from my iPad using Tapatalk

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Merlin

Merlin

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We hear about light loss in binoviewers, but we can only wonder how much light is lost in the 12" APO bins. In view of the amount of glass the light has to pass through, and including reflection and absorption, probably quite a bit.

As a point of interest, a third of the light entering the Yerkes 40" refractor never reaches the eyepiece.

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Zakalwe

Zakalwe

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Posted

I used to go to HK on a regular basis. Fantastic city with fantastic people but I must admit it wouldn't be my first choice location for housing a scope like this. The pollution, both light and smog is quite significant at times.

Hong Kong Island and Kowloon are particularly bad for light pollution. It might be better in parts of the New Territories but then the smog rolls in from Shenzhen.....

Stuart

To be fair, the bloke that owns these monster binos also has two robotic observatories in Tibet- one at 4300 metres altitude, the other at 5100 metres. Jammy git! :grin:

http://www.astrocafe.hk/viewtopic.php?f=12&t=1188&start=280#p14562

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