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Review - William Optics Binoviewers

Posted: 8 November 2014

photo Binoviewer
William Optics

While helping out in the OPT booth at the Arizona Science & Astronomy Expo, 1-2 November 2014, I purchased a William Optics Binoviewers from OPT. One of the OPT employees in the booth had high praise for the WO Binoviewers so I decided it would make a nice addition to my visual accessories.

This review will discuss using the William Optics Binoviewers on two telescopes: my 8" LX200-ACF in the observatory and my ETX-105PE.

The binoviewers, two included 20mm eyepieces (66° AFOV; Wide Angle), and a 1.6X Barlow Lens are nicely packed in foam inside the box:


It also includes caps for all holes. However, only one end cap is provided for the Barlow Lens, which seemed odd. There is no instruction sheet, although a sheet describing the two year warranty is included.

8" LX200-ACF

I mounted the binoviewers on the 8" telescope using a 2" star diagonal with a 1.25" eyepiece adapter, as seen here:


Just as with binoculars, you can adjust the eyepieces separation for individual eye-to-eye distance. I slewed to the moon and rotated the entire binoviewers for comfortable viewing. Next, I focused the right eyepiece using the telescope focus knob. The left eyepiece was then focused by rotating its eyepiece holder (the right one can also be focused by rotating its holder). With both eyepieces in-focus I could see that focus was excellent over the entire field-of-view (FOV) at 100X.

And oh wow, what a view of the moon! It was no longer just a flat surface, but had a very obvious "globe" look to it. Of course, the 3D effect is just an illusion from using both eyes. Along the terminator the views were absolutely incredible.

I added the Barlow Lens, which screws onto the 1.25" nosepiece using the filter threads. (The Barlow Lens will also accept a filter.) Lunar details at 160X were amazing. Hills and mountains really looked like they were extending upward from the lunar surface. I definitely have a new favorite way to view the moon! Using the binoviewers I will be rediscovering what our moon has to offer.

My next object was M57 (Ring Nebula) at 160X. Even though the sky was bright due to a waxing gibbous moon, the Ring Nebula was easily seen using both eyes. In fact, it seemed slightly brighter with both eyes vs viewing through one eye alone without using binoviewers. Just another of the benefits of using a binoviewer. At 100X (no Barlow Lens), M57 was a pretty sight. But the brightening effect was less apparent at 100X. I also viewed M45 (Pleiades), low in the eastern sky. The view of individual stars was good, although the entire cluster was not visible in the FOV.

As the telescope was slewed from object to object, it was always necessary to rotate the binoviewers to provide a comfortable view while sitting down. That's because the orientation changed as my wedge-mounted telescope with star diagonal was pointed in different directions.

I returned to the moon and spent some time just enjoying the 3D view. I noticed that details on the moon seemed sharper when using both eyes. In fact, I saw some details on the moon which I had never noticed before. This is a result of the brain doing its magic to improve what you see when using both eyes. To confirm this effect I removed the binoviewers and viewed the moon using one of the 20mm eyepieces. The 3D effect was gone. The image quality was excellent, but the lunar details were not as sharp (due to atmospheric seeing) as when viewing with both eyes.

I did some solar observing using the Binoviewers with the 20mm eyepieces and an 8" full-aperture solar filter. Details on the sun were very distinct even though seeing was pretty bad due to strong breezes and the sun's low altitude in the sky. I added the Barlow Lens; the views were still good. Two eyes are better than one.

I did a check using the Binoviewers with a separate Meade 2X Barlow Lens:


Viewing the moon using the separate Barlow Lens was effectively the same as with the included William Optics 1.6X Barlow Lens.

I tried to use the Binoviewers with my 3X TeleExtender, but got a surprise. The 1.25" nosepiece of the Binoviewers would not go into the 1.25" eyepiece hole on the TeleXtender! Obviously the Binoviewers nosepiece goes into a 1.25" eyepiece holder since I've used it on my telescopes. My 1.25" eyepieces all fit fine into the TeleXtender. Really odd that the Binoviewers won't work with the TeleXtender.

On another night, prior to moonrise but with some lingering twilight and a brightening sky from the moon, I did some Deep Sky Object (DSO) observing using 20mm (100X on my 8"). M17 (Swan Nebula), low in southwestern sky; shape was visible. The globular clusters M13, M92, and M56 were all very nice. M57 (Ring Nebula) was good. Epsilon Lyrae (Double-Double Star) was a nice view; all four stars were visible with the two close components being nicely separated. The colorful double star Albireo was a beautiful sight with both eyes. M31 (Andromeda Galaxy) seemed to be floating in space; a neat effect from using both eyes. M32 (galaxy) was visible, but M110 (galaxy) was difficult due to its faintness and the brightening moonlit sky. M27 (Dumbbell Nebula) also seemed to be floating in space. And one side of the "dumbbell" appeared to be closer to me than the other side. Just another neat side effect of using both eyes. M33 (Triangulum Galaxy) was faintly visible. M76 (Little Dumbbell Nebula) was easily seen with both eyes. The most striking effect of using binocular vision was seen while observing the Double Cluster. Both clusters were visible in the same FOV (barely) but with either cluster centered in the eyepieces an interesting 3D effect became apparent. Brighter stars appeared closer and fainter stars further away. This was due to the brain being tricked into thinking that fainter objects were further away. It may have been a fake 3D look but it was fascinating to see. I am going to enjoy rediscovering many DSOs as seen though the Binoviewers.

All my previous tests with the Binoviewers on the 8" LX200-ACF had been done without a focal reducer. While viewing the Double Cluster I began to wonder about reducing the magnification and increasing the FOV. I added the f/6.3 focal reducer to the 8". Unfortunately I could not reach a focus with the Binoviewers using its 20mm eyepieces on the 2" star diagonal (seen in the above photos). I removed the diagonal and using the visual back alone the Binoviewers did focus. Both clusters of the Double Cluster were well inside the FOV. I added a small 1.25" diagonal to the focal reducer, as seen here:


I could focus the image, but just barely before running out of focus travel. The view of the Double Cluster at this low magnification was pretty.

While using the focal reducer I also viewed the just past full waning gibbous moon. The entire disk was visible in the FOV. This handheld iPhone 5s afocal photo (full-frame) through one of the 20mm eyepieces gives a good idea of the wide field-of-view while using a focal reducer:


I removed the focal reducer and did some lunar observing. When I switched back to a single 2" 24mm UWA eyepiece, the views of the moon, while very nice, were rather disappointing by comparison after having used the Binoviewers for lunar observing!


As shown below, the Binoviewers fit fine on an ETX-105PE:


I viewed a nearly full moon using the 20mm eyepieces and no Barlow Lens. The entire lunar disk was inside the FOV, but just barely. The details were sharp all the way to the edge. The 3D effect was not as pronounced on the ETX has it had been on the 8" telescope. Adding the 1.6X Barlow Lens provided great views of the lunar surface. The two-eye sharpness effect was noticeable on the ETX. Viewing of the moon was very comfortable when using both eyes.

I also viewed M13 (Hercules Globular Cluster) and M57 (Ring Nebula) with and without the Barlow Lens. The bright moonlit sky hampered viewing of these DSOs but they were visible. Both were best viewed without the Barlow Lens. On these DSOs the two-eye increase in brightness effect was very evident.


One might think that having a binoviewer would make doing some types of astrophotography easier. One side could be used for the camera and the other side for centering an object or maybe for even doing manual guiding. I tested this capability to see how viable it would be.

I first tried an iPhone afocal setup:


That's a live moon image on the iPhone 5s. The earbud/mic volume buttons are used as a remote shutter release for the iPhone. I used two Meade Series 4000 26mm eyepieces from two of my ETX telescopes in the Binoviewers. The iPhone is attached to its eyepiece using my modified MX-1 Afocal Adapter.

With this setup I discovered two minor problems, both of which had easy workarounds. The first problem was that the two "identical" eyepieces were not parfocal. In fact, they were not even close to being parfocal. After focusing the telescope for one eyepiece I had to slide the other eyepiece a short distance outward in its holder to get it to focus. The second problem was that the weight of the phone and adapter would cause the Binoviewers eyepiece holder to rotate (which is how the focus can be matched for both eyepieces). The solution to that problem was to put the adapter in an orientation that did not cause the rotation.

With this setup, afocal astrophotography of objects can be done. Here is the moon, taken with the iPhone 5s:


Some smartphones and cameras, including small point-n-shoot ones, should work for this type of astrophotography. Guiding on objects for longer exposures should also be possible, as long as your guide eyepiece and your imaging eyepiece can both be focused. Depending on the size of the camera, you may need to adjust the eyepiece separation distance to accommodate your head and camera.

I then tried using my Nikon D7000 DSLR. This is the camera mounted at prime focus (no eyepiece):


One problem becomes apparent from the photo: there is no room for your head if you want to have your eye close to the eyepiece. But that was a minor problem compared to the one I experienced when trying to focus the eyepiece. I had to slide the eyepiece entirely out of the eyepiece holder by almost an inch to reach a focus when the image in the camera was in focus. Unless you have a 1.25" extension tube for eyepieces, using the Binoviewers for prime focus astrophotography will not work.

I also tried an eyepiece projection setup using my OPT Camera Adapter:


The William Optics 20mm eyepiece that is included with the Binoviewers fit perfectly inside the adapter tube. I could focus the image in the camera, but the other eyepiece needed to be held about a 1/4-inch out of the eyepiece holder to reach focus. I also tried using a 9mm eyepiece in the eyepiece projection adapter. But with the camera in focus, the other eyepiece needed to be 1-inch beyond its holder. Again, an extension tube can eliminate this problem with the non-camera eyepiece. But the size of the camera and your head will dictate whether you can actually look through the eyepiece while the camera is mounted.

Bottom line: you can do some types of astrophotography using binoviewers, but the depending on what accessories you have it may be difficult. And since the object brightness as viewed in each side of the binoviewers is reduced by 50%, if your goal is to do guided exposures you would be better off using an off-axis guider adapter instead of binoviewers.


The William Optics Binoviewers is a very high quality accessory, both mechnically and optically. Viewing bright and faint objects using both eyes is more comfortable and can even let you see things that you might not have otherwise seen. There is one drawback to owning a binoviewer however. You may want to expand your eyepiece collection so that you have several matching sets of eyepieces for use in the binoviewers. The included 1.6X Barlow Lens and having a focal reducer can help stem this desire, at least for awhile.

You can find more details about the Binoviewers at the William Optics web site.

If you are a dedicated lunar observer, you will absolutely enjoy using high quality binoviewers. This is likely the main reason for purchasing binoviewers. But once you have them you will probably find yourself using them for planet observing and some DSO observing. I know I will.

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