I wanted a smaller, lighter finder ‘scope for the Astrola, and I wanted right angle to stop straining my neck!
I have been using a big Orion 9x60mm finder on the Astrola, the only telescopic finder ‘scope I have among the Telrads. It is nice, with a bright image that shows many faint fuzzies. It is also huge, and very heavy, it is also straight through, requiring one to crane your neck around to view through it on the Newtonian ‘scope.
A small, lightweight finder was in order, a perfect project for a newly arrived 3D printer.
The design is simple, three parts. The tube, a forward lens shroud, and a mount. The mount is the most complex part, including the adjustments needed to boresight the finder with the main telescope, and a dovetail foot compatible with the older Orion finder mounts.
The restriction is that the parts can be printed without supports. I was successful in designing everything this way. Indeed the design was good from the start, two of the parts printed from the original design, only the mount requiring some adjustment and a second print to make things fit properly. I got the dovetail a little tight and the dovetail screws a little high.
The front shroud is printed from TPU rather than the usual PLA used in most 3D printing. TPU is a soft, flexible material, thus the shroud is flexible to the touch and can stretch slightly to fit over the front end of the tube. The only issue with TPU is it needs to be printed slowly, very slowly… It took a while.
The objective lens is not secured by the front cap. That was the original plan, but I realized I could not guarantee a tight fit and holding the lens completely secure. Instead the front of the tube is sized at exactly the same diameter as the lens. Some wide Kapton tape secures the lens to the front of the tube. This is very secure and Kapton will not degrade. It can be easily removed if needed for cleaning or repair.
The diagonal is an old junkbox part that has been sitting around for years. I have a whole crate of this stuff, odd telescope bits that continue to come in useful. Unlike many finders this uses standard 1.25″ eyepieces, thus I can change the magnification if desired.