BORG 90FL APO Fluorite Binocular Telescope (AOK)



Objective diameter:  90 mm
True aperture:  90 mm
Focal length:  500 mm
Focal ratio: f/5.6
IPD:  59 – 80 mm
Focus type: IF
Waterproof: no
Weight (measured, w/o eyepieces, with eyepiece cover and objective caps): 5‘980g
Made in: Japan



Borg of Japan produces a line of astronomical telescopes, components and accessories for the hobby markets. A special characteristic is the modularity of Borg’s product lines; this allows for a huge number of combinations and even the possibility of combining Borg components with third party elements. The instrument presented here has at its core Borg’s 90mm tube with the very good f/5.6 Canon Optron fluorite doublet ( see a recent review of this tube at: ). Swiss astro shop AOK of Lucerne has combined two of these Borg tubes and mounted them on a purpose-built platform to make a binocular telescope, each tube fitted with a high-quality Kasai double-speed focuser and a Matsumoto EMS (“Erecting Mirror System”). The end result looks perhaps a bit “technical”, but this binoscope has a number of advantages over the ready-to-go competition from Kowa, Vixen, APM or Oberwerk:
Mechanically and optically excellent, it is amazingly compact and lightweight, and the user can easily and quickly self-perform the conditional alignment of the two tubes (which allows for high magnifications without double images), simpler and faster than on other binocular telescopes. This together with the  fluorite optics permits observations at magnifications well beyond 100x, according to some users even up to 200x, e.g. for planets or moon.

See separate posts about

“Kowa Highlander Fluorite 32×82”,×82/
“Vixen BT-81S-A”,
“Vixen BT-ED70S-A”,
“APM 82mm ED APO”,
“APM 70mm ED APO”,
“Oberwerk BT-100XL-ED”,
“Oberwerk BT-82XL-ED”,

Ratings / Reviews:

A brief report about initial impressions can be found here:

(posts # 64 – 69, scroll down)

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