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Adapting Eyepieces for Binoviewing

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Adapting Eyepieces for Binoviewing.

by John C Raymond



John Raymond is a lifelong resident of Virginia. He received his first telescope Christmas Day 1980. Past president of the Richmond Astronomical Society. Ten year volunteer for the NEAF Solar star party.


I've enjoyed binoviewing for a few years now. What drives me is the question: What works best for binoviewing? Among the various discussions in the Binoculars and Binoviewing forums on  Cloudy Nights is the mention of IPD or Interpupillary Distance




Successful binoviewing entails one major requirement: both eyes must receive light from the objective. Now this sounds kinda obvious, right? Well it's not that easy. Most astronomical binoculars and binoviewers are hinged. This allows the two eyepieces to be spaced so that light enters both eyes. Some of us have a narrow IPD and facial structure that prevents optimal eye placement. In my case, the nose. It won't fit between some binocular eyepieces. It won't fit when binoviewing with complex, wide body eyepieces.


Ok so why is this an issue? Why not stick with simple design Plossl and Orthoscopic eyepieces that allow plenty of schnozzle room? For the moon and planets I find the simple designs quite sufficent. But for me it's not just binoviewing, there's also Deep Sky Binoviewing. Here wide field is a consideration. We use large complex eyepieces for monoviewing deep sky. We want wide field, long eye relief, and freedom from aberrations in one package.


The Pentax XL

This widefield, long eye relief eyepiece has been a favorite of observers for almost twenty years now. A sensation when they first arrived, they quickly established a good reputation. At the star party there was always that one Pentax guy, a lone heretic who used these exclusively, and endured the kind-hearted ribbing of the TeleVue enthusiasts.   (Myself included)


Only this year did I consider these eyepieces for binoviewing. They are light, have long eye relief, and a wide field. Available on the used market only. To adapt these for binoviewing: remove the rubber eyecup. Unscrew the aluminum skirt. Be careful of the threads, they can be sharp! There is grease that requires removal too.


The resulting eyepiece is much slimmer. It's unmarked too, so I added. “21” with gold Sharpie. The ink is reflective making for easy identification with dim red light. Then a 40mm rubber eye guard like this




See the pictures! Dramatic increase of interocular space.





TeleVue Delos

I first tried these at a star party right after they were introduced. I was really impressed! These feature long eye relief, wide field, and perfect views. The adjustable eyecup is  quite wide however. When binoviewing I have to hold my head at an angle as my nose can't fit in between. To adapt these for binoviewing: unscrew the two barrels of the eyecup. Be careful, the compression ring can fall out. Likw the Pentax, the inner barrel is unmarked. I write the focal length on it with gold sharpie. The eye lens is an odd diameter, the only eyecup that fits is the Baader EYECP-2 for 33-34mm.




In my 18” dob, I prefer the 17.3 Delos over the 24 Panoptics.




The TeleVue Delite

The Delites offer 20mm eye relief and excellent optics. The small size appears perfect for binoviewing, but again my nose says otherwise. The adjustable eyecup unscrews just like the Delos. I found useable eyecups on EBay, under microscope accessories. Look for the 35-40mm size. There are many sellers offering a variety of eyecups. Be a wise shopper and read the descriptions carefully. Most of the sellers have pictures giving the dimensions of the eyecups. 






The Televue Radian

This was TeleVue’s long eye relief line of eyepieces since replaced by the Delites. I find these to be excellent on Jupiter. Can be found used at bargain prices, compared to the current offerings. I also found eyecups on EBay, The 33mm size with sloping profile called “Oxhorn” by some sellers.   








  • vkhastro1, Lewis Cason, RAKing and 1 other like this


Great article! A subtitle could be "Lose a Little Weight, Gain a Little Light".
    • Augustus and Allanbarth1 like this
Aug 29 2017 02:27 PM

I realized that when I was beta testing the first Denkmeier bino-viewers. I first limited myself to Plossls because even 2 of them in a bino-viewer was better than one eye with a Nagler. Even though I knew the spacing would accommodate 2 Pentax XLs I did not think it would also fit my nose so I limited myself to cheaper and smaller 60-70 degree eyepieces (and besides I didn't want to have to buy expensive eyepieces in pairs) like the older Antares W70. Still plenty good enough for bino-viewing.

    • Astronomerforfun likes this
Aug 29 2017 09:47 PM

Many de-shroud the 18mm 82AFOV Meade 5000 UWA.  I have one and someday hope to have two for binoviewing, though I don't know if I have the guts to actuall de-shroud mine.



I use Vernonscope  Brandon 24mm eyepieces with Denkmeir binos equipped with a power switch.

They work awesomely well and since I use them more for Solar Viewing they are amazing at doing that.The contrast is very very  good.

I'm new to the binoviewing movement. I waiting for Denis to ship the pair I bought from him along with the ep's he suggested. Waiting for funds to clear. This article caught my eye. 


John, thanks for writing this article.


I'll also heading over to the bino forum.


You missed one big possibility to greatly enhance the BVing experience-use a pair of high quality zooms !

After getting to look thru a pair of Baader Mk4's this summer, I knew a zoom setup had to be on my bucket list.  I will have a Mk4 some day soon for mono, and maybe a pair out in the future.  But for now I picked up a pair of the little Nikon 7-21 zooms at a super bargain price and they have me a happy BVer.  The flexibility to dial in the perfect magnification without having to swap (let alone buy more pairs ! ) eyepieces has really changed the BVing game for me.


With the 1-2X switch on the BVer I have a continuous, step-less, range of EP's from 3.5 - 21 mm  smile.gif

It would take some collection of EP pairs to match that.




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