So much discussion in this thread it's difficult to find a starting point.
I have to convince myself I can test a mirror before buying a blank etc.
Just looking for confirmation that I am doing things correctly.
I have built a foucault tester based on the Stellafane model and have a silvered completed 8" GSO mirror to test.
From the attached images can anyone tell me if:
1. The position of the LED looks OK. Just above the slide hole for full passage of light to the mirror.
2. I have aligned the returned mirror reflection (small circle) back to the knife edge.
3. I have moved the knife edge to the radius of curvature (twice the focal length). On my mirror focal length 1200mm/47.244", f/5.9 making ROC at 94.49 inches.
4. I have observed the returned beam at its smallest and most focused to confirm its at ROC. I have moved the tester closer and further away from the ROC.
Problem is, I am not getting the expected shadow either side of ROC.
At exact ROC the light is very bright.
Is this to be expected when testing on a completed silvered mirror?
