This is a 3d model of a cap used to aid in collimation of the Celestron 127EQ newtonian reflector telecope. This was described by niuno15 in this thread:

http://www.astronomyforum.net/celestron-telescope-forums/98045-improvements-celestron-powerseeker-12...

This is placed inside the main telescope tube, onto the bottom of the focuser, and provides a target for the reflected laser beam to hit.

This method is also known as the barlowed method, because it makes use of a barlow lens. The Celestron 127EQ has a "barlow" kind of built in to compensate for a shortened tube. This makes conventional collimation difficult, but lends well to this barlow method.

This process is described here as well for normal newtonian reflectors:

https://www.cameraconcepts.com/barlowed%20laser%20collimation.pdf

Anyway, I modeled this in Openscad, and the scad file is included, so feel free to change some parameters around.