A t high magnifi cations, a microscope's fi eld of view is much smaller than the region of interest. Pathologists examining suspected tumor sections overcome this limitation by translating the section. Biologists assessing cell division in a cell population undertake a more quantitative analysis, examining multiple images that cover a region of interest. Currently, these tasks cannot be performed using a single digital widefi eld image. We have been investigating two approaches that use digital

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... Fourier holography to accomplish them more effi ciently-ultimately automatically. 1,2,3 of microspheres, we have used a Mietheory inversion routine to automatically determine the local scatterer size in the images. We have shown that such a routine works well even on discocyte red blood cells. Th is spatially resolved particle characterization is obtained from a single wide-fi eld capture without resolving the individual scatterers-in a sense, a form of superresolution. Th e product of spatial and angular resolution is invariant, but resolving the Mie-theoretical oscillations leaves suffi cient spatial resolution for many applications. We have also exploited Fourier holography's direct access to a sample's spatial frequency spectrum. 3 Instead of the conventional wide-fi eld imaging approach of recording a large spatial frequency range over a narrow fi eld of view, we record a small spatial frequency range over a wide fi eld of view. In both cases, a set of images is required to build up the wide-fi eld, high-resolution image. However, our synthetic-aperture approach has the intrinsic advantages of a low-numerical aperture objective: no immersion and centimeter working distances. With a collection objective of 0.13 NA, we have demonstrated superresolution equivalent to a synthetic aperture of 0.72 NA. Challenges remain in how to perform particle characterization when Mie theory breaks down, and how to correct for off sets and complex scaling factors when combining holograms. Even so, there are excellent prospects for effi cient, fl exible wide-fi eld microscopic characterization based on Fourier holography. t