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  • Ville Puoskari

Ultra compact travel scope

Recently, my fascination with observing the beauty of southern skies led me to contemplate the idea of bringing even larger optics on my future travels. However, the challenge lay in making it both portable and cost-effective. Determined to find a solution, I embarked on a DIY journey to create a telescope that could be easily shortened for air travel and assembled with minimal tools once finished.

To keep costs down, I opted for a 114/900mm Newtonian primary mirror and a 25x35mm optical flat secondary mirror, both sourced from Amazon at a surprisingly affordable 40€. While the price tag was modest, the potential for decent image quality for wide field deep-sky observing loomed large, making it a worthwhile experiment. With the mirrors in hand, the next challenge was constructing an optical tube assembly (OTA) to house them. Traditional machining proved too complex with the tools at my disposal, leading me to consider 3D printing. After many hours of design and printing using PETG filament on my Bambu Labs P1P printer, I successfully crafted the necessary components.

The truss tubes are 20mm aluminum tubes sourced from a local hardware store. They are glued in place with superglue, resulting in a surprisingly rigid tube weighing a only 2.5 kilograms, including the focuser and dovetail bar! Collimation seems to hold steady at all angles, as I spun the telescope around with a collimation laser around at different positions. Here are some photos of the build as I progressed towards my goal.

A brief test on Messier 45 showcased round and crisp stars with some expected astigmatism and coma towards the edge of the image. I would take a different approach on a larger mirror but with such a light weight design I took some liberties to cut down on the weight as much as possible without sacrificing too much on the rigidity of the OTA. This custom telescope is likely to bring the cosmos even closer within reach for me on my next observing trip.. I cant wait! If you wish to build your own, all of the files are available on Thingiverse. I recommend printing all of the parts with at least 20% infill and ~2mm wall thickness or more on all walls to keep the structure as rigid as possible. Print the secondary mirror holder, primary mirror base and all of the clamps (including finder shoe) for tubes as a solid object as these are subjected to a highest loads.

Post-printing you will require some additional parts listed below. • Sky Watcher focuser, with 80mm flange (I use 2" Crayford Focuser for Sky-Watcher Explorer Newtonian series) • Vixen dovetail bar with flat top, roughly 200mm length (accurate length doesn't matter as the mounting is adjustable)

Secondary mirror assembly: • 3x M4 threaded inserts • 3x 40mm long M4 bolts • 1x 70mm long M6 bolt. • 1x M6 wingnut

Primary mirror assembly: • 3x 50mm M6 bolts • 3x M6 nuts • 3x 10mm springs, approx. 20mm in length.

Middle joint assembly: • 6x 50mm long M6 bolts • 6x M6 wingnuts • 3x ⌀ 20mm and 350mm long aluminum tubes (from secondary mirror assembly to middle joint) • 3x ⌀ 20mm and 450mm long aluminum tubes (from primary mirror to middle joint)

Secondary mirror assembly: • 2x M4 threaded inserts • 3x M4 / 50mm bolts

Dovetail attachment: • 4x M6 / 40mm bolts • 2x M6 ~40mm bolts (length may wary depending on dovetail) • Some M6 washers to act as a spacer

Finder shoe: • 2x M4 threaded inserts • 2x M4 / 50mm bolts • 2x M6 / 70mm bolts • 2x M6 nuts

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