Hi Neil,
Nice work on the tester
I'm in the process of building my first foucault tester too, so it's good to see the various approaches in this thread.
I noticed you had no setup yet for measurement, were you planning on using a dial gauge? I purchased one but am having a great difficulty working out how to mount the thing solidly. It only has a flat base so nothing to screw into, I think I will need some kind of clamp setup. The stellafane plans are quite vague about this.
If anyone has any suggestions/examples that would be excellent
Quote:
Originally Posted by nobby2
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?
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