102mm (4") Newtonian Telescope

thingiverse

This is part of a series of experiments to create telescopes using primarily (consumer) 3D printed parts (optics aside for now, although we have plans in that area as well!) and is a direct follow-up to my 'pandemic hack' 6" Newtonian https://www.thingiverse.com/thing:4294635 This is a better designed (optically at least) 4" (102mm) Newtonian Reflector (the one pictured has a focal length of 700mm). It includes an adapter to use a Raspberry Pi V2.1 Camera at prime focus. You may notice that the camera in the picture is a Raspberry Pi HQ which simply attaches via a c-mount tube. The eyepiece holder does not include a thumbscrew, but that can be easily added (you may want to modify the holder to make it longer for your application anyway). I have included both STL and fusion 360 archive files for your convince. The reason this model uses such long printed mounts was to allow me to use 500mm extruded aluminum rails (unlike the longer ones used in the pandemic hack which are over 600mm). It uses quite a bit of material to be sure, and the housing tubes could be replaced with something as simple as Bristol board or ABS pipe (but again this was meant as mainly a 3D printing hack). The one place I deviated from this, was the use of 4" toilet flanges for the Dobsonian mount rather than printing them. Although not pictured (this was a temporary base for testing) you will likely need some kind of strap to add friction over the top of the mount. As pictured tested well however. All parts were designed to be printed within a 200mm cube volume There are some parts in the picture not included here that relate to a rail mount focusing attachment that needs refinement/redesign (it suffers from some slight racking). The primary mirror was attached to the cell using silicon latex caulking (it's what I had...). The cap screws that you can see the mirror resting on in the image are removed after the caulk as cured allowing the mirror to 'float' on the caulking in the cell (there are holes for the caulk to flow through to hold the caulk pillars fast in the cell). Unlike the 6" hack, the secondary mirror was glued to felt using flexible adhesive, which was in turn glued to the cell/mount. You will require an assortment of m5 hardware, 4 appropriate sized springs for the kinematic adjustments (I used 15mmx9mmx1.3mm heatbed compression springs which work well for both 1/4-20 and 5mm capscrews) and some smaller screws for the secondary kinematic adjustments and raspi camera adapter. I would recommend flocking (might be problematic if you are focusing by moving the secondary on the rails - certainly you can focus using the eyepiece as well as per normal) or lining the scope with some mat black Bristol board to improve the contrast. This was designed to use standard 1.25" eye-pieces unlike the 6" hack. I hope you enjoy!