You can build a holographic microscope for $250 (for parts), MIT Technology Review Physics arXiv Blog reports.

Holographic microscopes record the 3D shape of tiny objects such as cells in high resolution, unlike traditional microscopes, which have a tiny field of view and shallow depth of field.

With a holographic microscope, you make a hologram of the sample: split a laser beam in two, use one as a reference beam and bounce the other off the sample to record the pattern of phase shifts that this produces using a digital camera. Recombining the beams produces an interference pattern that can be analyzed to retrieve 3D information about the sample in high resolution.

Kisarazu National College of Technology in Japan experimenters have provided plans (Ref. below) for building a small portable digital holographic microscope using a web camera, a small solid state laser, an optical pinhole, and free open-source software.