Stellafane 2008 - Al-Paslow
Foucault Tester close up. Notice it uses a dial indicator and has what appears to be a "precision slide". This device measures the longitudal shift in the traversing light & shadows that are visible on the tested optic.

Foucault Tester close up. Notice it uses a dial indicator and has what appears to be a "precision slide". This device measures the longitudal shift in the traversing light & shadows that are visible on the tested optic.

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