measured AFOV

I just learned how to measure the Apparent Field of View (AFOV) of an eyepiece. It's super-simple!

Set up a rig and tested my 36mm 2" aspheric eyepiece. Quick and crude, I computed the AFOV at 71.2°. baader planetarium says it's 72.

Do you see the large faint illuminated circle?

We can use the technique to measure the antique ocular at the DDO.

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Tip of the beanie to the Cloudy Nights article "eyepiece afov calculation" with discussion, diagrams, and photos as well as the CN article "flashlight test for aperture - illustrated" on using a torch.