We modify the optical transfer function of an incoherent imaging system such that it is nearly invariant to misfocus and contains no zero values. Digital filtering of the resulting image restores the image to near diffraction limited spatial resolution. A system that is insensitive to misfocus is also insensitive to some lens aberrations. Consequently, the approach of combining optical and digital signal processing system extends the normal aberration balancing of lens design to include those aberrations that can be reduced by digital signal processing, such as spherical aberration.© (1996) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.