Cost-effective ultra-depth-of-field Fourier ptychographic microscopy.

Fourier ptychographic microscopy (FPM) is a promising computational imaging technique that achieves high space-bandwidth product (SBP) quantitative complex amplitude imaging through synergistic integration of phase retrieval and synthetic aperture methodologies. However, conventional FPM struggles with defocusing issues when the sample exhibits non-planar distribution characteristics or is positioned at a non-ideal pose, which can cause the sample to be beyond the system's focal range, degrading the quality of the reconstructed image. In this paper, we propose a cost-effective solution to achieve ultra-depth of field (DOF) FPM. With the defocus distance calculated from the lateral shift under oblique illumination, we can drive a photographic lens, which serves as a tunable tube lens, to refocus along the axial direction. By computationally fusing reconstructed images acquired at distinct focal planes using FPM, the system achieves ultra-DOF while preserving native imaging performance. Experimental results show that the DOF of a 10× objective with a numerical aperture (NA) of 0.25 can be significantly extended from 9.24 μm to 300 μm, achieving an improvement of up to 30 times.