Well, I finally went ahead and built one of these for purposes of checking collimation and also for optical testing.
It was cheaper and easier to do than I had thought. The main challenge is in making a proper size pinhole.
The size of the pinhole depends on the aperture you want to test. In my case, it's not too crazy. My main scope is my TSA-120, < 5" aperture.
Reading Suiter's book, I conclude that a hole of 50micron diameter or less will be fine, at a distance of at least 20X the focal length.
To make the pinhole, I used thin copper foil I had at work. I flattened a small piece on a smooth piece of glass and then, using a fine sewing needle
I carefully poked small holes in the foil. As you push the needle, you slowly spin it. This creates a fairly nice, round hole.
Where I work, I have access to electronic microscopes with measuring capability. With a bit of practice (1 hour) I was able to routinely create
nice pinholes of 40micron diameter and smaller. I then just save these foil specimens.
The case I used is a small, plastic case large enough to fit a 9V battery in it.
For the light source I used a Green, Ultrabright LED. This I got from Digi-Key for $0.24 (#C503B-GAS-CB0F0791-ND).
It has a brightness rating of 53650 mcd.
I drilled a hole in one end of the plastic box and mounted the foil on the inside. I installed a rocker switch and run the LED through a resistor off the 9V battery.
Pretty simple. To protect the pinhole I just put a piece of masking tape across the hole in the case!
Edited by NHRob, 31 August 2014 - 11:40 AM.