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eyepieces for binoviewer

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I finally to the plunge and ordered a Baader Maxbright binoviewer (1.7x corrector) plus T2 Zeiss prism diagonal for my f/7 110 apo on a hand driven mount.

While I am waiting for the bino to arrive I am looking for a few suggestion for eyepieces to observe planets and double stars from my suburban garden.

Above all I am wondering what magnifications would be useful.

I have a pair of 25mm orthos and single orthos 18mm, 9mm and 7mm to start with. Would it be a good idea to get a pair of 12.5mm orthos and double up the 7mm orthos?



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Hi Andre,

We are in the same boat! I too am waiting for a binoviewer to arrive and am considering my eyepiece options. I have an f/8 102 apo (and the Zeiss prism diagonal) and am waiting on a Denkmeier standard. I recently picked up some nearly new 12.5mm orthos which will give me around 40x per inch (factoring in the 2.5x OCS). I think 40x per inch is as high as I will go until I get some first-hand observing experience with the binoviewer. Although my primary interest is in the planets I am currently thinking that I will also go for a pair of EPs with a field stop approaching the clear aperture of the binoviewers (26mm). Maybe a pair of 25mm orthos or 32mm Plossls (not sure how much the latter would vignette though). I will be able to use the Denkmeier at 1.4x as well as 2.5x so want to avoid buying EPs that will be too similar in mag depending on the OCS configuration.

If you double up on your 7mm it will give you around 40x per inch for high power, however I have read that the shorter an EP’s focal length the more chance that some people will have problems merging the images as imperfections in the binoviewer’s prism may come into play more. Maybe the 7mm and 9mm would be too short? Have you considered adding a barlow element before the diagonal? It seems that some users of the Mark V Baader binoviewer user a 2x barlow element in various configurations (the Astro Physics BARCON appears popular) before the diagonal and in conjunction with a glasspath corrector to allow longer focal length EPs for high mag work.

Maybe other SGL members with more experience could comment on what they consider the shortest focal length EP they are comfortable with when binoviewing ?


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