A lens that is \"optically perfect\" is still limited by diffraction effects. Su

Question

A lens that is "optically perfect" is still limited by diffraction effects. Suppose a lens has a diameter of 140mm and a focal length of 700mm .

A. Find the angular width (that is, the angle from the bottom to the top) of the central maximum in the diffraction pattern formed by this lens when illuminated with 520 nm light.
= ? rad

I tried - 1.22(520-9)/ 140*10-3 = 4.5e-6 NOT RIGHT! Don't know how to solve!!!

B. What is the linear width (diameter) of the central maximum at the focal distance of the lens?
2y = ? m

Explanation / Answer

Lens diameter is D = 140 mm

                                  = 140 *10^-3 m

focal length f = 700 *10^-3 m

a ) sin = 1.22 / D

               = 1.22* 520 * 10^-9 m / 140 *10^-3 m

               = 4.53 *10^-6 m

         = sin ' ( 4.53 *10^-6 )

            = 2.59*10^-4 rad

b ) linear width is   y = s

                                      = 700 *10^-3 m * 2.59*10^-4 rad

                                        = 1.813 *10^-4 m

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