A camera photographs a matt lawn of radiance

PHYSICS · Multi-part · Fermi University Physics · Optics & Photonics · Geometrical optics and imaging · Geometrical optics and imaging

Optics and Photonics, Ch Radiometry and photometry

Problem

A camera photographs a matt lawn of radiance L=60 W m−2 sr−1L = 60\ \text{W m}^{-2}\ \text{sr}^{-1}. The lens is lossless and the object is far away, so the image-side irradiance is Iimage=πL/(4f#2)I_{\rm image} = \pi L/(4f_\#^2), where f#f_\# is the f-number. ((a)) Find the irradiance on the sensor at f/2.8f/2.8. ((b)) Find the irradiance on the sensor at f/8f/8. ((c)) State the ratio of the two irradiances and check it against (8/2.8)2(8/2.8)^2.

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