Characterization of the image quality of a wide angle MWIR f-theta objective lens by means of pixel contrast

摘要

Objective lenses for missile warning systems have typically a wide field of view of about 120° to 180° In order to get a inear correlation between object angle w[rad] and image height y[mm] they have a f-theta correction, with the focal length f[mm] as correlation factor. Usually the image quality criteria for optical systems are specified with MTF- or Strehl-values. In this case the image quality is indicated as pixel contrast defined by the amount of energy from a point source falling on one pixel compared to the amount of energy of the same source falling onto the neighboring pixels The image of a point source from infinity is the Airy disk, which has a circular shape provided that the pupil is also circular In order to get correct values for quadratic pixels the ensquared energy has to be taken. The size of the Airy disk is correlated to the f/# of the optical system and the wavelength. There is an interconnection between dimension of the optical system f/#, Airy disk and achievable Pixel contrast. These dependencies are discussed for a recently developed 168° field of view objective lens.