by John C Raymond
I’d like to share some of my ideas and opinions on binoviewing.
What is a System of Binoviewing? An assembly of common observing equipment that’s powerful, portable, easy to use, effective, and fun to use. In my experience Binoviewers enhance the observation of Targets of Excess Light (moon, safe solar, and planets) I believe that given a half-decent telescope, most amateurs will see a much greater benefit from Binoviewing than upgrading any single optical component.
Let me first give a summary of the 3 main telescopic observing systems used by recreational amateur observers.
The first system is what I call Monoviewing. This is the ancient and original mode of telescopic observing, and most commonly seen today. One telescope and one eyepiece at a time. So common that we don’t even think about the wonder of it anymore. When someone says “I used my telescope last night to look at the moon.” We usually assume this is the system used. Monoviewing has many advantages and only one main disadvantage for me. The main advantage is using 2″ eyepieces for extremely wide fields of view. The disadvantage: At high magnifications on bright targets (exit pupils less than 1.2mm) the floaters in my observing eye become annoying and degrade the view. (1)
Binocular Viewing is using both eyes with a telescope. Binocular viewing encompasses two main systems: Binoviewing and True Binocular Viewing.
Binoviewing is using a beam splitting device (binoviewer) to allow use of both eyes with one telescope. Using both eyes is our natural mode of vision. The binoviewer simulates True Binocular Viewing with only one telescope.
Binoviewing works wonders for me on the moon and planets. I have the advantage of relaxing by keeping both eyes open (I HAVE to close my non viewing eye when Monoviewing.). The effect of floaters is reduced, allowing me to use much higher magnifications than Mono. There is the advantage of Binocular Summation, which I understand as: using two eyes over one, more than doubles the amount of data the brain collects from the view. I experience this effect myself, and is probably the reason myself and many other binoviewer users are so passionate about these devices. I see increased detail with a smaller aperture, than Monoviewing with a larger. The degrading effects of atmospheric seeing, scope thermals, and miscollimation are attenuated. Binoviewing is even recommended by John Westfall in his book, “Atlas of the Lunar Terminator” (2)
As an experiment, one night at a public viewing I let some 8 to 12″ dob owners try the binoviewers on Jupiter. The effect was the same: all reported, and I verified, a substantial increase in detail, resolution, and overall aesthetic of the view. At the same magnification, Jupiter appears much larger with two eyes versus one. I hear and read a lot of talk about improving ones planetary views with a better objective, diagonal, or type/brand of eyepiece. Oh what they don’t know!
Binoviewing does have some major disadvantages. First, not everyone is able to use both eyes. Not everyone can merge the images in a binoviewer. The binoviewer must be well collimated, or it’s useless. Some binoviewers, while well collimated, have eyepiece holders that can tilt the eyepieces out of line. Binoviewers add weight and balance issues. There is the expense of matching eyepiece pairs. Commonly available units are limited to 1.25″ eyepieces. In my experience Binoviewers dim views on Targets of Deficient Light (most DSO’s) when used with small aperture scopes. For larger apertures I’m undecided. On brighter DSO’s it’s wonderful. For critical viewing of dim targets Monoviewing has the advantage. The one exception is Night Vision binoviewing, that wondrous technology outside the scope of this article. (3)
Binoviewers simulate, but do not provide, True Binocular Viewing. When I first tried Binoviewing I expected much more than the laws of physics allow. They don’t double the aperture of the scope!
Another major hindrance of Binoviewing is reaching focus with the telescope. I’ve heard many stories from frustrated binoviewing newbies who can’t reach focus with their equipment. I’ll explain how I deal with that when I describe my setup.
True Binocular Viewing is the best form of viewing. One eyepiece and telescope for each eye. The smaller instruments are referred to as Binoculars, the larger Binocular Telescopes. There is no official dividing line between the two and considerable overlap. Handheld Binoculars comprise a large and successful segment of observation. How many books and articles have been written about it? What advice is commonly given to beginners? “Buy a pair of binoculars instead of a telescope.” Why? Easy to use. Nice wide fields. Lots to see.
True Binocular Viewing is what we all strive for, as it’s our natural mode of viewing. For both low and high magnification viewing, for both planetary and deep sky, nothing beats this system. While the practical application is extremely successful in small sizes, it does not size up very well. Binoculars larger than 50mm are generally too heavy to hold for extended periods and require mounts. Sizes 100mm and above have significant issues of price, portability, ergonomics, and availability.
The largest production binocular of the common refracting type is the Fujinon 150. (4) The price and weight are too much for most amateurs. Only one company, JMI, regularly advertises Newtonian Binocular Telescopes (5). Custom Binocular Telescopes using commercially made refactors were available for a time from the Binoscope Company and Borg/Hutech (6).
Many reflecting Binocular Telescopes have been made by amateurs. (7) These offer larger apertures, but are heavy and take up a lot of space. Viewing with these requires the observer to face away from the target. The collimation of Binoculars is even more critical than that of Binoviewers. With binoculars not only must both telescopes must be collimated, but also collimated with each other. Any misalignment in Binocular optics is intolerable.
In my observing career, I have used all three of these systems to good effect. My binoviewing system described below is the results of years of trying different telescopes and eyepieces to find that “best” planetary viewing that works for me. The components are high quality and easily available. I can deploy this system quickly in my backyard. It’s not very heavy. I’m very satisfied with the views.
Selecting the telescope and other gear
I must admit I’m a telescope junkie. There are a few of us around. They guy who shows up with a different telescope every time. I can say the first iteration of my system was ten years ago with a D&G 6″ f/12 refractor (8) on a Losmandy G11 (9) mount. I found these locally, used, and the price was right. What an amazing telescope! More refractors and Maksutovs followed, and then a AP 900 (10) mount that held a 5″ f/22 custom D&G refractor (11), a New Moon Telescopes 12.5” f/6 Dob (12) , and most recently an AP 5″ f/12 Superplanetary. The 12.5” Dob and big refractor I had to sell due to layoff at work last year. Without a permanent observatory, a large heavy scope lost its appeal . I needed something portable and easy to set up.
My observing buddy also had a number of nice scopes; the most memorable a Takahashi TSA-102 (13) I remember the perfect images and star test, the many planets and double stars split in that most excellent refractor. Takahashi recently introduced the FC-100DF (14), a 100mm f/7.4 doublet. I like doublet refractors. This scope has been the perfect instrument for my needs. Attains wide field with a 2″ eyepiece, solar with a Herschel wedge (15), and best of all: lunar/ planetary with Binoviewers. Now 740mm may seem too short for decent high power viewing, but the Binoviewers use a 2x corrector at minimum. It’s much easier to double the magnification of a telescope than halve it. The scope is short and lightweight, so score points for portability and ergonomics. I added a Feathertouch (15) for fine focusing mandatory for my high power planetary viewing.
I found a good deal on a Losmandy GM8 equatorial mount. I had one before, but never really had the perfect telescope for it. I was always chasing the big scope for my larger mounts. The GM8 is small portable enough that I can lift the entire mount, tripod, counterweights and all, and carry it from my porch to backyard. With the large mounts it was carry this piece, then that piece, then the counterweights, then the thing I forgot, then the next thing I forgot…
A simple rough alignment with the polar scope and it tracks well, quietly, for hours.
The Binoviewer is the TeleVue BinoVue (16) It came to me with a used scope several years ago. It sat for a couple of years before I even gave it a try. If only I can go back….
The BinoVue includes standard a 2X amplifier. Based on Televue’s instructions on reaching higher magnifications (17), I soon tried the two inch 2X and 4X Powermates. I can tell no functional or optical difference when using the 2X Powermate vs the amplifier. The 4X is even better. The 4.3x amplification(TV chart) raises the scope’s effective focal length to 3182mm, allowing use of long focal length eyepieces for planetary viewing. Generally these have longer eye relief and larger eye lenses then short focal lengths. I find these features provide more comfortable viewing.
Selecting eyepieces
My criteria for planetary viewing are optimal magnification and exit pupil. I like a minimum magnification of 100X, and a maximum that seeing conditions will permit. Here in the Mid-Atlantic nights of good seeing are rare. For exit pupils I prefer a minimum of 1.2mm when Monoviewing. With binoviewers I can use pupils as small as 0.6mm comfortably.
Chart 1 shows the magnifications and exit pupils provided by a range of eyepiece focal lengths. With the 4X Powermate my eyepiece selection is in the 30-15mm range. My lowest mag is 106x, good for public outreach session. Eyepieces in the 20mm range provide a 0.6mm exit pupil for usual viewing. For those steady nights a 15mm gives 212x and 0.47mm exit pupil. This is the smallest exit pupil recommended by the RASC (18).

With this setup I’ve been able to view Jupiter almost every clear night. The GM8 and 4″ refractor are a powerful planetary observing system with all the advantages. Easy to set up, portable, lightweight, optically excellent. The only disadvantage is that it’s ONLY a 4″ scope…
During the period where I assembled this system, my 18″ Teeter Dob (19) was in the shop getting a makeover. Jupiter loves aperture. Once at a star party we had 12.5″, 15″ and 20″ scopes lined up in a row. Each larger scope showed an increase and detail, color, and resolution. It was a powerful lesson at the time. Let go back to the eyepiece chart and see what some aperture does.
According chart 2, my preferred eyepiece range is in the 20 to 10mm range. Any higher and we hit the general upper limit on magnification. (20) Interestingly enough, the Dob with 2x amplifier provides the same focal length as the refractor with 4X. But look at the exit pupils. I run out of magnification long before exit pupil! My best planetary viewing has come from this fast, f/3.5 scope!

Chart 3 is an expansion of Chart 2, listing eyepieces between and 18 and 11mm

Deep Sky Binoviewing has its rewards too. And pitfalls. Like I stated above, I’m very ambivalent about Mono vs Bino with the big scope. I like both! There is the comfort of using two eyes. The increased resolution from binocular summation. The light lost by halving the aperture to each eye. The limiting fov of 1.25” eyepieces. To me DSO binoviewing is more about comfort than improving image quality.
I hope this article is helpful. I apologize for any errors or omissions.
Regards,
John Raymond
Richmond VA
March 2016
References
- http://www.skyandtelescope.com/astronomy-equipment/a-pupil-primer/ return to article
- http://www.cambridge.org/us/academic/subjects/astronomy/amateur-and-popular-astronomy/atlas-lunar-terminator?format=HB&isbn=9780521590020 return to article
- http://www.cloudynights.com/page/articles/cat/articles/night-vision-astronomy-2015-three-perspectives-r3028 return to article
- http://www.fujifilmusa.com/products/binoculars/lb150/index.html return to article
- http://www.jimsmobile.com/buy_rb.htm return to article
- http://www.sciencecenter.net/hutech/borg/bino/index.htm return to article
- http://arieotte-binoscopes.nl/
http://www.jerryoltion.com/binoscope.htm return to article - http://www.dgoptical.com/refractor.htm return to article
- http://www.losmandy.com/ return to article
- http://www.astro-physics.com/
http://teebark.com/teebark_test/wp-content/uploads/2013/04/solar_observing_201304.jpg
return to article - http://www.astromart.com/classifieds/details.asp?classified_id=867715 return to article
- http://www.newmoontelescopes.com/ return to article
- http://scopeviews.co.uk/TakTSA102.htm return to article
- http://www.landseaskyco.com/takahashi-takahashi-fc-100df-refractor-telescope.html return to article
- http://starlightinstruments.com/store/index.php?route=product/product&path=37_80&product_id=124 return to article
- http://www.televue.com/engine/TV3b_page.asp?id=63 return to article
- http://www.televue.com/engine/TV3b_page.asp?id=63&Tab=_ause return to article
- http://www.rasc.ca/handbook return to article
- http://www.teeterstelescopes.com/ return to article
- http://www.philharrington.net/sw2.htm return to article