A larger, virtual image appears behind the observer if he is standing closer than the focal length of the convex type.
One type of these devices is capable of producing Bessel beams with minimal diffraction. Another types of these devices is created by layering a set of concentric annular sections. Their bestform type minimize comas formed from deviations from the optical axis. One formula sets the difference between inverse radii proportional to their power, which is measured in (*) diopters and is equal to the inverse of focal length. A larger, virtual image appears behind the observer if he is standing closer than the focal length of the convex type. For ten points, identify these optical devices contrasted with mirrors, which are curved and found in microscopes and glasses.
One type of these devices is capable of producing Bessel beams with minimal diffraction.
lenses [accept specifics like concave or convex lenses]