Moonfish Binoviewers

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Brand and Model:Moonfish Binoviewers
Price ($USD):129

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Moonfish Binoviewers
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I will admit to being a bit of a sceptic about binoviewers. I’ve always thought of them mainly as a great marketing ploy to get gadget–mad astronomers to buy more stuff and to double the size of their eyepiece collection. I’d tried looking through a pair at Jupiter through a friend’s 10” LX200 and I just couldn’t get on with them. So when Daniel Corredor of recently e-mailed me asking if I wanted to review their binoviewers I was flattered, but fully expected to be posting a less than glowing review on Cloudy Nights. I’ve been a fan of Moonfish’s Widescan range of wide angle (70o FOV) 1.25” eyepiece for a few years now, having purchased both the 15mm and 20mm examples and was so impressed that I posted reviews of them on Cloudy Nights (

The binoviewer and additional eyepieces to supplement my exist Moonfish eyepieces arrived well packaged and in good order. As usual, they arrived when Moonfish said they would. Oh that all companies were this reliable! The binoviewer came in a neat little flight case-style foam lined aluminium box and the additional 15mm and 20mm eyepieces in bolt bottles. The binoviewers were tested out on my trusty polar-mounted ETX 90EC.

I decided to start observing with a gorgeous 7-day old moon. First I looked through the 20mm and 15mm Moonfish eyepieces with no binoviewer. Both gave the expected sumptuous sharp-almost-to-the-edge wide field of view I have come to know and love from Moonfish Widescan eyepieces.

Next I inserted the binoviewer and a single 20mm eyepiece. There was a definite small loss of brightness, presumably caused by the glass in the BAK 7 glass prisms in the binoviewer. The view was still sharp and contrasty. Next I put in the left hand eyepiece and waited to be under whelmed. ….

Oh, how wrong I was! The Apennines leapt out of the eyepieces at me. The difference was very marked. This was no subtle change in nuance that only the seasoned observer will appreciate if they stand on one leg and stare through the eyepiece at it without blinking for three hours. This hits you like a train coming at you! Craters look deeper, mountains soar into the night sky and valleys turn into bottomless crevasses. If you are a regular visual lunar observer you simply have to get a one of these; the only debate should be when, not if.

Looking at Mars and Saturn the differences were less marked than for the Moon, but were none the less noticeable. These planets definitely took on a more spherical appearance, standing out from the inky jet of the night much more markedly than through a single eyepiece. And here I think I might have stumbled across part of the reason for why binoviewers make things stand out more. They seem to create a very marked increase in contrast. I don’t think this is the whole reason, but it’s definitely part of the answer. It seems to me that the use of the binoviewers made brighter objects advance and darker object recede, increasing the feeling of depth. This was noticeable when viewing the Orion Nebula (M42), where the stars of the Trapezium seemed to sit on top of the nebulosity, whereas with a single eyepiece one gets the impression that they are embedded within it. Similarly, Saturn seemed to stand out in front of Titan with the binoviewers, but produced a relatively flat view in a single eyepiece.

Another thing you need to take into account when assessing the effect of binoviewers is that they increase the length of the light path, thus increasing the focal length and hence magnification and contrast.

With the ETX 90 the use of binoviewers did create a couple of problems, but neither of them were insoluble. Firstly came the problem that the binoviewers couldn’t be positioned perpendicular to the OTA because the ETX finderscope got in the way! Simply adding an extension tube such as Astroengineering (AC543) Extension Tube or the Scopestuff (#EEX1) 1.25" Eyepiece Barrel Extension would solve the problem. I used an extension tube made by Chris Livingstone Telescopes. Please note that the 1” long eyepiece extension marketed by Scopetronix (Item – STEPEXT) is not long enough.

Secondly, there is the matter of weight; binoviewers are heavy. The Moonfish binoviewers weigh in at 500g. Add the additional extra weight of an extension tube and an extra eyepiece hanging off the back and the little ETX motors started to strain a bit. However, I have a homemade counterweight system which easily coped with this extra weight. The Astroengineering system (AC025 + AC026) should work equally as well. Whether these measures are needed on the much larger ETX125 I do not know. Certainly on scopes with a slightly more beefy drive than the ETX 90, or when using with counterweights, this shouldn’t create a problem.
Interestingly, one of the nights I tried the binoviewer, I had problems with dew and then ice. The large chunk of metal and glass that is a binoviewer resulted in increased dewing which took longer to clear with a dew zapper gun. This dewing caused a lowering of contrast and large reduction in much of the 3D effect of the binoviewers.

The combination of the Moonfish binoviewers and Moonfish eyepieces were very comfortable to use and gave a great feeling of an expansive, immersive view. However, to get the very best benefit of this feeling, you have to get your eyes close up against the eyecups, and on the ETX, this caused some slight vibrations in the less than solid ETX mount. On a scope with a better mount, this shouldn’t be noticeable.

In summary: Are binoviewers an unqualified improvement to all visual observing? No. However, if you are a lunar observer, owning a pair of binoviewers is simply a must. In my eyes, there is no debate (excuse the awful pun). Planetary observers will definitely gain some increased enjoyment when using binoviewers, but the improvements are less marked. For doubles and deep sky objects I couldn’t see any great improvements in viewing. In fact, for very faint deep sky objects and faint doubles, I found a net decrease in object brightness when using the binoviewers. For me, as a keen observer of the Moon and planets, these are a definite hit and a great investment at only £79/€119/$129. Well done Moonfish on another great product. I’m also planning to order their much vaunted 30mm 2” Ultrawide eyepiece and highly recommended 1.25” Astronomiks UHC filter for use with my soon-to-be-purchased Orion 80ED and 8” Meade LX200 set up.

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