Answer:
A flat lens is a lens whose flat shape allows it to provide distortion-free imaging, potentially with arbitrarily-large apertures. The term is also used to refer to other lenses that provide a negative index of refraction. Flat lenses require a refractive index close to −1 over a broad angular range.
Step-by-step explanation:
Plano - A plano lens is a flat lens. This is used when one side is flat and the other side is concave or convex. You can think of flat as a "plain."
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