Patent ID: 7612316

Claim:
A focus detection device comprising: an objective lens to observe an observation sample; a transparent member having a refractive index that is different from a refractive index of the observation sample; an illumination optical system, including a light source, to project illumination light from the light source through a peripheral portion of the objective lens so that the illumination light is reflected by a boundary face between the observation sample and the transparent member; a detector to receive the reflected light from the boundary face through the objective lens; a condensing optical system to condense the reflected light on a detection surface of the detector; a position controller to move the objective lens and the observation sample relatively; and a controller to control the position controller based on the reflected light from the boundary face detected by the detector to perform focus detection; wherein the focus detection device further comprises: a shutter to shield the reflected light, wherein the shutter is insertable into and removable from an optical path of the illumination optical system; and a focus detection lens that is insertable into and removable from the optical path of the illumination optical system; and wherein the focus detection device is configured to switch between (i) focus detection carried out by inserting the focus detection lens into the optical path and removing the shutter out of the optical path, and (ii) fluorescent observation carried out by removing the focus detection lens out of the optical path and inserting the shutter into the optical path, thereby illuminating the observation sample with evanescent light.