The 3-D reconstruction of light microscopic objects has been extensively investigated in the past, but fundamental problems remain. The real object under observation does not normally have high transparency, and light transmission will be attenuated introducing nonlinearities in the imaging process. A nonlinear approach to this problem has been developed. In this nonlinear approach the authors regard the 3-dimensional spatially resolved light absorption coefficient as the object information of interest. A nonlinear equation system modeling the imaging process is proposed.