Hi all,
I have just completed a simple ronchi tester, mainly to help me understand how these things work. I used a program called grating to make the grating and had a LED shining through the transparency which was at the centre of curvature of my 8" f7 mirror. The same grating extended out so I could have my camera there to take a pic of the return beam. This was only a test and so far it is starting to work, but there is alot of blurring of the lines, its quite possible I need to diffuse the LED more make a smaller slit for the light to go through and use a real ronchi screen
Anyway here is one of the first pics from it. The blocks holding the mirror can be seen on the bottom.