Hsin-Yueh SUNG, Sidney S. YANG, and Horng CHANG¹

Institute of Photonics Technologies, Department of Electric Engineering, National Tsing Hua University, 101, Section 2, Kuang-Fu Road, Hsinchu 300, Taiwan, R.O.C.
¹Industrial Technology Research Institute, Electronics and Opto-Electronics Research Lab., 195, Section 4, Chung Hsing Rd., Chu-Tung, Hsinchu 310, Taiwan, R.O.C.

(Received July 14, 2008; Accepted February 6, 2009)

A different approach, aiming to achieve the constant blur status of point-spread function (PSF) at a certain defocused plane, is described. The correlation between the two PSF is used to control the PSF blur similarity, and simultaneously the Strehl ratio is also used to control the PSF blur minimization. By designing the PSF so that it is significantly insensitive to defocus or related defocus quantity, for example, due to temperature change, all the constantly blurred images can be accurately de-blurred by a simple inverse restoration filter for an adequate range of defocus. We refer to that as “software lens compensation” and apply a design method to solve the athermalization of middle wavelength infrared (MWIR) imaging systems. The resultant PSF is almost invariant in the temperature range from -10 to 50 °C at the same focal plane. Consequently, the constant blur spot can be removed by a simple digital signal processing. Thus, clear and sharp de-blurred images at different temperatures are obtained.

Key words: point-spread function, blur similarity, depth of focus, focus compensation, computational imaging, infrared imaging, athermalization, lens design