A Compact Schlieren Optics Device for Imaging Biological Samples

Conventional Schlieren optics equipment typically operates on a large optical table, which is inconvenient for imaging small samples or thin layers of transparent materials. We describe an imaging device based on Schlieren optics, aided by a slight shift in light reflected from two surfaces. The device is designed to place the sample between a thick concave mirror and a camera next to a point-light source located at the spherical origin of the concave mirror. The compact device is portable and convenient. It is similarly capable of sensitively detecting patterns in gaseous or liquid media created by a density gradient when the optical effect is too subtle to be detectable by regular cameras and scanners. The new device is particularly suitable for detecting translucent samples, including thin fluid films on the order of micrometers, tissue slices, and other biological samples. We show two examples of how our device can be applied to imaging biological samples. The first compares images acquired using several techniques of a bacterial swarm spread over an agar plate; the second is a set of images of human cells grown on a tissue culture plate. Key features • The protocol presents the design of a compact Schlieren optics device (CSOD), with image boundaries enhanced by a slight shift in two overlapping, virtual images. • The CSOD captures high-resolution images of a transparent medium with variation in thickness or index of refraction. • The CSOD can detect transparent samples with thickness in the order of 1 µm; it is simple to build, user-friendly, and portable. • As a cheaper and portable complement to a phase contrast microscope, the device can image large samples more conveniently.