Hello. I need some sort of explanation. I was unsuccessfully trying to find information on the web and derivation by hand seems rather complicated for me. So I have a such set-up: HeNe laser ->> plano-concave lense )], light is incident by some angle (NON 0°). then looking to reflection screen I clearly see two reflections and one of them (smaller) having clear Newton's rings pattern. As I understand it is interference between the first surface (concave) and the second surface (plane) reflections. My question is: can I somehow determine RoC from this pattern (attached)? The pattern seems to be sensitive to orientation and position of the lens.