Illumination Calculus in Imaging Optics

When designing an imaging instrument with a sensor, it is important to calculate radiometric quantities, in particular spectral irradiance, at the image plane. Muschaweck shows how to adapt the way these calculations are made in illumination optics to the imaging situation. The approach is based on fundamental laws of optics: Conservation of etendue, conservation of radiance along a ray, and the definition of irradiance (power per area) as the integral of radiance over the two angular dimensions of phase space.

With datasheet information about the sensor, i.e., pixel area, spectral quantum efficiency, full well capacity and integration time, we can calculate where the sensor signal lies between the fundamental shot noise floor and clipping.

As an example, Muschaweck shows how to calculate the shot noise level as a function of integration time for a hypothetical space telescope looking at Jupiter. He uses only (i) that the telescope is F/4 with 85% transmission; (ii) that it has a Sony IMX 455M sensor; (iii) Jupiter's diffuse reflectivity of about 50% and its distance to the Sun; and (iv) the radius and temperature of the Sun. Muschaweck also shows why additional quantities such as Earth-Jupiter distance, Jupiter’s size, the telescope’s focal length and field of view have no effect on the result. As an additional example in the accompanying material, he applies the same calculus to a machine vision application.

About the presenter
Julius Muschaweck, a German physicist, has been working on optical design for illumination for over 25 years. After a stay as visiting scholar at the University of Chicago with Professor Roland Winston, well known as the originator of Nonimaging Optics, for research on concentrating on sunlight, he cofounded and became CEO of OEC. OEC was a unique illumination optics research institute plus optical engineering service that pioneered tailoring freeform optics for illumination. Later, at OSRAM, the LED maker, where he held the position of senior principal key expert, the highest rank in the Siemens/OSRAM expert career, he coordinated over 100 optical designers within OSRAM worldwide. He then joined ARRI, the leading movie camera and lamp head maker, as principal optical scientist. Muschaweck now works as an independent consultant and author, providing illumination optics solutions to industry clients, teaching courses on illumination optics, and writing about the subject.

He is the author of over 25 scientific papers as well as a SPIE tutorial book, Designing Illumination Optics, and the inventor of over 50 patent applications. He also loves to go hiking and camping with his wife and their dog. You can learn more about etendue and illumination optics at his website: https://www.jmoptics.de.