Hill's Space

8" Telescope Mirror Parabolizing: So close...

 |  1 min  |  121 words
A spreadsheet of mirror measuring information
A graph generated by the spreadsheet that shows the mirror's slope compared to the ideal slope
My mirror in the testing setup, with a piece of cardboard blocking parts of the mirror at known radii so I can measure where each part of the mirror is focusing light to. It's set up for the Foucalt test, so the right hand side of the image is darker than the left, showing that those parts of the mirror focus light outwards from where I'm measuring.
This mirror in the Ronchi test, for reference.

I’ve switched to using the Foucalt test and a Couder mask for parabolizing. The Foucalt test is more precise (but more annoying) than the Ronchi test, but my local astronomy club has a foucalt testing rig with a micrometer that lets me measure very precise details of where different regions of the mirror focus light, so it’s more accurately moveable than my handheld Ronchi tester. I built a cardboard “Couder mask” to block off regions of my mirror to see where the edge and center are focusing light to separately. I need to take so many measurements for this Foucalt test, which is time-consuming. I also built a spreadsheet to help me interpret the results. I’m so close to perfect parabola…

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