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Earthwin PFS-B Binoviewer


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I live in a light polluted area in central Mass near Worcester. I have been an amateur astronomer since 1973 and have built telescopes, made mirrors and bought telescopes. Over the course of my amateur career, I have had a 6" refractor, 10" classical cassegrain, 8" sct and more and currently have and use a 16" dob mounted reflector and 10" meade sct and an 6" Criterion RV6 as a travel scope.

At NEAF in 2008, I purchased a new PFS-B binoviewer from Earthwin optical to use with my 16" scope. This is the unit that has the 3X power switches and the ability to slide 2 different filters in and out, one at a time.

I have had a year of experience with the binoviewers and at this point, seldom use single eyepieces anymore when observing. I use a pair of 35mm televue plossl eyepieces with the binoviewer primarily and find that I seldom have the need to ad higher power except on very bright objects like the moon at which time, I switch out the 35mm's for a pair of 17mm televue plossls. The 35mm eyepieces have a nice, wide field of view that works well with these binoviewers. With the 3 power feature, these seem to have the right combination of both wide field of view and more than adequate magnification at higher power.

After a year of experience, I can say that mechanically, the binoviewers are still working solidly, no mechanical or collimation issues.

What I like about them:
  1. The ability to switch between 3 different powers without having to remove eyepieces and put a barlow in is a great. Sitting and observing an object, sliding a power switch in or out is so much easier to do.
  2. I really enjoy being able to slide one of 2 filters in and out of the field of view while watching the object I'm observing at the same time. It's a great help for seeking out things like planetary nebulas and beats the old way of holding onto the filter and passing it in between my eye and the eyepiece. As above, using this is a lot easier than pulling the eyepiece out and screwing / unscrewing filters like I used to do.
As with any other accesory like this, while not heavy as binoviewers go, they are heavier than just an eyepiece. I had to upgrade my focuser to handle the extra weight and to help keep the optical path true even when the binoviewers were racked out.

Opitcally I have found that they are excellent with good, sharp pinpoint star images. The collimation is good, though some of that depends on whether or not the eyepieces you use are in the eyepiece holders true or not. There are adjustments for the eyepieces and locking rings to help keep things in alignment.

I have compared the view with the binoviewers to single view eyepieces I have and have noticed no difference in quality. I have a 25 mm televue wide field and a 2 inch older vernonscope erfle to compare. I have not had the opportunity to compare the binoviewers to some of the newer eyepieces out there.

I have found that I am able to see fainter objects a little more clearly with the binoviewers and with less eye strain than with single eyepieces. For me, the relaxation of using 2 eyes simultaneously while observing has greatly increases my enjoyment. There is a noticable 3D effect with brighter objects like the moon and some of the brighhter globulars like M 13. One thing that I have found with the binoviewers is that the quality and sharpness of the view very much depends on how well your optics are collimated. If my collimation is off even a little bit, the view is degraded with some flaring. This was true with a lighter duty focuser, thus my need to get a heavier duty focuser to keep things in line. The binoviewers ahave a lot of latitude to adjust where the eyepieces are both in terrms of how far apart they are and where in rotation versus the axis of the telescope they are. This makes it pretty easy to get comfortable quickly.

The barrel end of the binoviewer that goes into the focuser is 2 inches, so the views are bright. I have 2 inch filters, the binoviewer came with 2 custom machined Delren holders with lock screws to keep the filters in place. I have since bought 2 more holders since I now have a collection of 4 different 2 inch filters that I use. One thing that I do wish is that the filter slide had some way of accomadating all 4 filters instead of 2 at a time, but it is easy enough to slide any of the filters out and swap them. The filter holders also come with plastic storage cases, so overall, dealing with the filters is safer and cleaner with this system than without.

One area that I have found that the binoviewers are not so hot for is star parties. Everyone has a different set of eyes that each need to be adjusted for and that slows things down, so I generally go to a single eyepiece if I've got multiple guests waiting for a view. Not everyone seems to like the view thru a binoviewer either. Some people seem to have trouble adjusting to the view. For me however, once I have everything adjusted for my eyes, I have found that overall the views are bright, comfortable and easy.

Earthwin has made a solid, quality product that if you like binoviewers, is easy to use reliable and of high quality. Their customer service has been first rate too. Oh and the black and gold color scheme? I've never noticed what color any of this is in the dark.

Steve Hubbard
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