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Two best focuses in APO?

Started by kulginov, 06/22/2006 03:18PM
Posted 06/22/2006 03:18PM Opening Post
In an achromat with C-like focal shift curve, the eye automatically picks the folding point as the point of the best focus (green light). Now, in a triplet APO with S-like curve, will there be two best focus points, one for each folding point - one for red, and one for blue? I'm primarily interestied in the real life experience, so doublet owners please don't bother smile

Dmitri
Posted 06/22/2006 05:01PM #1
The two focuses are indistinct. As you go through focus the Airy disk changes color from red-ish to white to blue-ish. At least in AP triplets.