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Binoviewers anhone?

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#1 Porkkala


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Posted 04 June 2020 - 05:02 AM

For context, I don’t even own a telescope yet. I took somebody’s advice and bought a binocular 20 x 80 and a parallelogram mount and started to learn the sky that way. I realized how much I enjoy the binocular view. Mine has a reported true field of view of 3.5 and apparent 70 degrees (but I suspect they are actually a bit less). I do understand TFoV and AFoV but perhaps one should also mint  “Subjective Apparent Field of View”. When I close one eye, I have the same AFoV as with two eyes, but somehow it seems less. My brain likes the twin view.


Now I caught myself wishing there was a way of buying a couple of new eyepieces for my binoculars. And I realize that I would be happy to pay for two, to get the binocular view, as opposed to saving money and get a monocular view. And then I learned that there is something called binoviewers for telescopes.


Maybe, when I do buy a telescope, I should buy a binoviewer and double sets of eyepieces? Those of you who have tried, did you like the binoview? Why? Why not? If you like it, do you use if for everything or only for, say, clusters? Are there any downsides, except for, obviously, cost? Would zoom lenses work in a binoviewer, or would it be hard to get the exact same zoom in both eyepieces?


How would you compare the subjective apparent field of view of a single 100 degree EP to a 68 degree binoview?  Am I likely to get disappointed by a binoviewer because there is actually no parallax and thus only an illusion of depth?


I’m a bit surprised that I have never heard of these before. My gut feeling would be that a binoviewer should be a superior way to observe. Coming to think of it, why do some birders use single tube telescopes? They should definitively benefit from binocular views. Is it only cost and portability?


I'm aware of technical issues like field stops and focusing, but for now I'm mainly asking about your subjective feelings and personal reasons for liking or disliking binoviewers. 


EDIT: I can't edit the headline. I meant Binoviewers anyone? 

Edited by Porkkala, 04 June 2020 - 05:08 AM.

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#2 Eddgie



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Posted 07 June 2020 - 12:25 PM

Binoviewers are a great way to view, but they do require some compromises.


First, because most binoviewers use a 1.25" eyepiece, you tend to be limited to narrower fields of view because most telescopes nowdays have 2" focusers and you can buy 2" eyepieces that give a much wider true field (not talking about apparent field).  The 1.25" limits you to eyepieces like the 24mm Explore Scientific or 24mm Televue Panotic for wide field views.


Next, because the binoviewer has a very long light path (the distance that light has to travel between the opening at the front and the eyepieces) most refractors and reflector telescopes will not reach focus without using some form of amplifier (Barlow lens of glass path corrector, or called by other names as well).  Since these raise the power, your true field gets even smaller.  


Now if you are buying new, SCTs will generally reach focus, but becuase SCTs are f/10, once again, you give up some low power, wide true field.  Still, a C8 with a binoviewer is a great little observing platform and most DSOs will easily fit into the field of a C8 with a binoviewer.


Also, some of the newer refractors out there  are also "binoviewer friendly" meaning that they can reach focus with binoviewers, though a special diagonal might be required.


One other limitation of the binoviewer is that unlike a binocular where each eye gets 100% of the light from it's lens, in a binoviewer, the eyes have to share one lens, so each eye only gets 50% of the brightness.


There is a binoviewer made called a "Linear Binoviewer" and this binoviewer gives each eye the full brightness, but it can't work well with the widest field 1.25" eyepieces, so you loose some true field.  Also, the Linear binoviewer works in almost all scopes, so no amplifier of glass path corrector is necessary.


As to how the viewing is, binoviewers are amazing (for most people) when used on solar system objects and while not quite as bright, give very immersive and comfortable views of DSOs. 


So, yes, you can view with both eyes and in spite of the compromises, a binoviewer is an excellent way to observe. 


Better still is an image intensified binoviewer.  About $2000, but with something like this, you can see the Horse Head nebula even from the suburbs using a small telescope.   These days I recommend an image intensified binoviewer over an expensive standard binoviewer because it turns a small scope into a large scope and lets you do great observing even from light polluted skies.  These will reach focus in all scopes and don't have the issue of light loss.  Not useful for planets, but a lot of people only do a lot of planets because the live in light polluted skies and that is all there is to look at.  With image intensifiers though you can see all kinds of stuff even from the city. 


PVS binoviewer - Copy.jpg

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#3 spereira



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Posted 07 June 2020 - 02:58 PM

Moving to Binoviewers for a better fit.



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