How Flat is Flat . . . and why should we care?

The folks at Lindsey Optics design some interesting macro attachment lenses as well as filters.  They have a new Zygo Phase Shift Interferometer.  Say what?  It’s a device that helps to ensure that their filters are as flat as possible.  Dwight Lindsey explains that any kind of curve in your filter essentially turns it into a lens and modifies the light traveling through it in ways that aren’t desirable.  Give it a read.

Source: How Flat is Flat . . . and why should we care? – Lindsey Optics