Artificial Star for Telescope Collimation

The use and pitfalls of using artificial stars for telescope collimation and testing are beyond my space here but are well described elsewhere. You can print this out of almost anything. Black is suggested. Use painted organic supports for the underside of the ball bearing post as shown in the photos. No other supports are needed. I suggest a 10% gyroid infill.

The #6-32 and 1/4"-20 threaded holes are modeled but you should carefully run a tap through them as they will typically be tight. The 1/4"-20 hole is a tripod socket, should you want to use one.

Find a shiny 1/4" or 6 mm ball bearing, clean it and gently retain it in the countersink with any handy #6-32 screw. A 1/4" long black oxide set screw with a cup point would be ideal, should your junk box have such.

Use a 3 mm white LED to provide the nuclear fusion for the star. I used a Digikey 160-1782-ND for about $0.54 each. Many others would work but you may wish to change the resistor value if the forward voltage is different. I aim for a current of about 1.7 mA for good battery life. I used 3300 ohms, but the precise value isn't critical. Measure across the resistor with a fresh battery and use ohms law to determine the current.

Don't be like me- try to remember to put the shrink tubing on the wire before soldering it.

My LED was a nice press fit, but if yours is loose, put a spot of glue on the back edge after you've put the LED in the hole. Also, note that the longer lead is positive. If you've cut it off and forgotten, there's also a small flat on the plastic next to the negative side, which is also the cup that holds the actual die.

A common snap battery connector is used and is also the on/off switch. The 9 V battery just sits in the box.

The FreeCAD file is included so feel free to modify this in any way desired. An ambitious person would put some dovetails on the sides of the LED post to accept a slide-on cover for the wires and to hide the illuminated back side of the LED.