Abstract: In order to be suited for long-term use in an enclosed space and to enable various modes of illumination by simple procedures and at a low cost without adding special optical components, the illuminating device for microscopes of the invention comprises a surface light source including a plural number of semiconductor light sources arranged in two dimensions, a control circuit selectively lighting some or all of the plural number of semiconductor light sources in conjunction with selection of an illumination mode, and an optical system for condensing and transmitting the light from the surface light source. The illuminating device of the invention makes it possible to observe a sample simultaneously in different illumination modes when the illuminating device is equipped with three surface light sources and the sample is irradiated simultaneously with the lights from the three surface light sources.

Abstract: A schlieren optical device using diode emitting monochromatic light as spot light source so as to have a compact and light-weight design, low calorific power, and low power consumption, and assure high reliability. In said optical device, imaging lens consists of a pair of lens groups arranged with an airspace reserved therebetween, knife edge consists of a light-shielding coating arranged on the surface of one of said lens groups and the other lens group is displaceable along the optical axis. Said optical device comprises a schlieren optical system and an optical system of a transmission type of microscope having optical axes perpendicularly intersecting with each other at the position of a sample, or a pair of schlieren optical systems and an optical system of a transmission type of microscope having optical axes perpendicularly intersecting with one another.