  Wide-field imaging is widely adopted due to its fast acquisition,
cost-effectiveness and ease of use. Its extension to direct volumetric
applications, however, is burdened by the trade-off between resolution and
depth of field (DOF), dictated by the numerical aperture of the system. We
demonstrate that such trade-off is not intrinsic to wide-field imaging, but
stems from the spatial incoherence of light: images obtained through spatially
coherent illumination are shown to have resolution and DOF independent of the
numerical aperture. This fundamental discovery enabled us to demonstrate an
optimal combination of coherent resolution-DOF enhancement and incoherent
tomographic sectioning for scanning-free, wide-field 3D microscopy on a
multicolor histological section.
