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Unobstructed Newtonian

"I have designed an optical system that can be thought of as an unobstructed Newtonian telescope," wrote Jose Sasian in Telescope Making #38. The design has the advantages of the Newtonian; a comfortable viewing position and the potential for a simple mounting. The secondary may be larger to avoid a turned-edge and left circular.

Which maketh Arcturus, Orion, and Pleiades
and the chambers of the south.
Which doeth great things past finding out;
yea, and wonders without number.

Jose Sasian relaxes behind the unobstructed Newtonian of his own design. The open frame telescope has doors which close over the optics for dust protection.
Details of Jose's toroidal secondary mounting and latching cover. The double curve is polished into this mirror by means of a simple jig.
Craig Engelhorn's rendition of the unobstructed Newtonian. The tube goes from being round at the primary to being oval at the secondary.
Front view of Craig's telescope reveals the secondary tucked out of the way. A Ronchi grating showed perfectly straight lines proving that double curve mirrors can be made well by amateurs.

Mirror Data
Primary diameter 150mm
Radius of curvature 3600mm
Figure paraboloid
Angle of tilt 2°.25
Distance to secondary 1400mm
Secondary diameter 46 x 65mm
Radii of curvature 5900 and
Angle of tilt 42°.75
Distance to image 365mm
System f/number 10.92
Focal length 1638
Image plane tilt

Author: David Stevick
[Weird Telescopes Page]

Curator: Hartmut Frommert [contact]
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