An aberration-free imaging technique based on focal depth extension

An imaging technique based on focal depth extension in active dynamic hollow cone illumination is proposed and discussed with respect to the influence of the system wave aberration. This imaging method uses a figure (numerical) 8 shaped narrow band-pass (for non-linear image reduction), sign correction (for amplitude/phase image selection) and median frequency range enhancement filter in the two-dimensional Fourier space. A simple analysis for the influence of the aberration shows that the present imaging technique is free from all primary aberrations except for astigmatism. In addition, the effect of higher order axially symmetric wave aberrations can be corrected by the use of the aberration map obtained from the diffractogram of the finally reconstructed image.