Lag1989 task №20.45

To reduce light losses during reflection from glass, a thin transparent film n = 1.3 is applied to the objective surface (n₁ = 1.7). At what is its smallest thickness dmin, the maximum attenuation of reflected light, the wavelength of which falls in the middle part of the visible spectrum (λ = 506nm), will occur? Assume that the rays are incident normally to the lens surface.