Lacerta Binoviewer for 31.7mm focusers

We're no Cyclops so see much more with two eyes than with only one. That can be proved easily by using a simple binocular. In case of astronomical telescopes usually only one eye can be used. This is where the binoviewer helps and provides a real 3D view of the Moon or the brighter deepsky objects.

The Castell binoviewer is based on big prisms to avoid vignetting even at low magnification. It provides contrasty images with minimum light loss. Image orientation is kept. Stray lgiht is reduced to minimum and has coating on all air-glass surfaces. Fits to 31,7 focusers. For eyeglass wearers +/-5 correction is available, inter-pupil-distance can be adjusted between 56 and 74mm. Size 120 x 60 x 150 mm, weights approx. 700 g.

Needs 108 mm of light path, which makes it impossible to use with Newton reflectors or eventually with some refracting telescopes as well. In this case a corrector is needed. The WO 1.6x corrector reduces the required travel distance to 47 mm, and the 2.5x version reduces it to 4mm. With this latter one the binoviewer can be practically used with a Newton reflector as well but the focal length is increased 2.5x times.

When choosing the magnification keep in mind that the human brain can detect 1.5 times smaller details if the object is seen by both of the eyes. Using eyepieces providing 100x magnification the same image might be considered as 150x. Keep in mind also that two identical eyepieces are needed.