Focus adjustment unit and optical scanning microscope

A focus adjustment unit used in a microscope system including an objective optical system that converts light from a specimen into a substantially collimated light beam and an imaging optical system that forms an image from the substantially collimated light beam of the objective optical system at a predetermined position, the focus adjustment unit being disposed between the objective optical system and the imaging optical system and configured to change the working distance of the objective optical system, in which a front side is defined as the side where the objective optical system is located and a back side is defined as the side where the imaging optical system is located, the focus adjustment unit comprising:

• a front-group optical system and a rear-group optical system that are sequentially disposed from the front side, each of the front-group and rear-group optical systems having refractive power;
• and
• a lens driver that drives the front-group optical system, or the rear-group optical system, or both, along the optical axis direction to change the relative distance between the front-group and rear-group optical systems along the optical axis direction,
• wherein the front-group optical system is disposed such that its front focal point is positioned sufficiently proximate to the back focal point of the objective optical system to maintain a small gap distance between the back focal point and the front focal point,
• wherein the front-group optical system is fixed, and only the rear-group optical system is moved along the optical axis direction in accordance with the following equation:
• |D1×δs|/(Fla)2≦0.05, where δs represents the total distance over which the rear-group optical system moves, D1 represents the gap distance between the back focal point of the objective optical system and the front focal point of the front-group optical system, and Fla represents the focal length of the front-group optical system, and
• |Fla|>|Flb|, where Flb represents the focal length of the rear-group optical system, and the front-group optical system has a negative focal length.

An optical scanning microscope comprising:

• an objective optical system that focuses light from a specimen;
• an imaging optical system that forms an image from the light focused by the objective optical system at a predetermined position;
• a focus adjustment unit including:
• a front-group optical system and a rear-group optical system that are sequentially disposed from a front side, the front side defined as the side where the objective optical system is located and a back side is defined as the side where the imaging optical system is located, each of the front-group and rear-group optical systems having refractive power;
• and
• a lens driver that drives the front-group optical system, or the rear-group optical system, or both, along the optical axis direction to change the relative distance between the front-group and rear-group optical systems along the optical axis direction,
• wherein the front-group optical system is disposed such that its front focal point is positioned sufficiently proximate to the back focal point of the objective optical system to maintain a small gap distance between the back focal point and the front focal point,
• a pupil projection optical system disposed behind the imaging lens, the pupil projection optical system converting the image of the specimen formed by the imaging lens at the predetermined position into a collimated light beam;
• a scanning optical system including a lateral scanner that laterally scans the light substantially collimated by the pupil projection optical system, a light emitter that emits light that illuminates or excites the specimen, a light receiver that receives the light from the specimen, a first collimator optical system that substantially collimates the light from the light emitter, a second collimator optical system that focuses the light from the specimen on the light receiver, and a detected light separator that separates the light from the specimen from the light from the light emitter;
• and
• a pupil position adjuster that moves the scan optical system in the optical axis direction of the pupil projection optical system so that the pupil position coincides with a point that is sufficiently proximate to the lateral scanner.