Build a 150mm Offset Binoscope

This project describes the construction of an ultra light 150mm Offset Binoscope. It is called an "Offset" binoscope because the two 6" F5 Newtonian reflectors are offset by 46mm which enables the two eyepieces to be angled at approximately 45 degrees to the long axis of the binoscope. This feature provides a much more comfortable viewing angle for the observer, especially as the binoscope orientation approaches the zenith. Ideally the mount can be adjusted in height so that the observer is standing more or less straight upright when observing the zenith and the eyes are at the level of the eyepieces. It then only requires a slight tilt of the head to observe comfortably through both eyepieces.

Another very significant advantage of this type of rectangular construction for the binoscope is that the two Newtonian reflectors are inherently co-collimated by the very compact and combined assembly, using precisely printed parts and aluminum angle struts. The more classic approach of independent Newtonian reflectors positioned either side of the head, where tertiary mirrors are used, demands much more accuracy and robustness from the mechanical structure.

As will be explained later, it is very important to finally glue black ABS plastic sheets (.062 inch thick, available through Amazon) to the sides of the frame to create a very strong and stable assembly as well as blocking stray light. Binoscopes can never be too rigid since even the slightest free play anywhere in the frame or mirror assemblies will lead to loss of collimation as the binoscope is moved around the sky. It is a good practise to glue most of the 3D printed parts to the aluminum frame once you are sure that everything works. Only the adjustable IPD top telescope focuser should not be glued. I use Devcon Plastic Welder, 2 part epoxy, as well as silicon RTV to glue the PLA or PETG parts to the aluminum frame.