Vignetting Effects: a Tool to Characterize a Fourier Ptychographic Microscope

Fourier Ptychographic Microscopy (FPM) is a recent technique to overcome the diffraction limit of a low numerical aperture (NA) objective lens by algorithmic post-processing of several lower resolved images. It can increase the space-bandwidth product of an optical system by computationally combining images captured under different illumination conditions. Vignetting determines the spatial extent of the bright field and dark field regions in the captured images that contain information about low and high frequency image content, respectively. State-of-the-art analyses treat vignetting as a nuisance that needs to be reduced or excluded from algorithmic consideration by means of ad-hoc decision rules [1]. In contrast, this work investigates vignetting effects as a tool to infer a range of properties of the optical system. To achieve this, we characterize the individual system components of the experimental setup and compare experimental data to both, geometrical and wave optical simulations. We demonstrate that using vignetting as an analytical tool enables the modeling of the geometric and coherence properties of the optical system as evidenced by the good agreement between our simulation and experiment. Moreover, our work investigates pupil aberrations in the FPM setup and enables their partial characterization, despite not yet encompassing all aspects.