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With the heatwave gone, I was finally able to test the primary mirror with my Bath interferometer.
When I made this mirror, I relied on zonal measurements with a Coude mask and Ross Null testing, during figuring. I did not have an interferometer back then, so I was curious to see how close I got to the required conic constant and if there were any significant zonal errors.
I wasted half a day trying to get sufficiently stable interference fringes until I realized that the laptop was blowing a stream of warm air into the light path. After that I managed to capture a bunch of usable interferograms. The optical design calls for the primary to have a conic of -0.7298 and my test today came in at -0.731, which is a lot closer than what I expected.
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