Editing Karl Schwarzschild (section)

===Physics of photography===
While at Vienna in 1897, Schwarzschild developed a formula, now known as the [[Schwarzschild law]], to calculate the optical density of photographic material. It involved an exponent now known as the Schwarzschild exponent, which is the <math>p</math> in the formula:

:<math>i = f ( I \,t^p )</math>

(where <math>i</math> is optical density of exposed photographic emulsion, a function of <math>I</math>, the intensity of the source being observed, and <math>t</math>, the exposure time, with <math>p</math> a constant). This formula was important for enabling more accurate photographic measurements of the intensities of faint astronomical sources.