This paper proposes a method of enhancing the indication sensitivity of image defocusing when energy conversion of the optical signal is used. It is shown that it is possible to use integral radiation detectors(photodiodes) in the electronic circuit of the converter.
S. M. Latyev, S. A. Sukhoparov, S. S. Mitrofanov, and I. N. Timoshchuk, "Increasing the sensitivity of a photoelectric defocusing indicator," J. Opt. Technol. 70, 653-654 (2003)