A 3-D optical microscope, a method of turning a conventional optical microscope into a 3-D optical microscope, and a method of creating a 3-D image on an optical microscope are described. The 3-D optical microscope includes a processor, at least one objective lens, an optical sensor capable of acquiring an image of a sample, a mechanism for adjusting focus position of the sample relative to the objective lens, and a mechanism for illuminating the sample and for projecting a pattern onto and removing the pattern from the focal plane of the objective lens. The 3-D image creation method includes taking two sets of images, one with and another without the presence of the projected pattern, and using a software algorithm to analyze the two image sets to generating a 3-D image of the sample. The 3-D image creation method enables reliable and accurate 3-D imaging on almost any sample regardless of its image contrast.