Abstract: A dual focus optical system for causing the images of two objects separate from each other on the optical axis to be formed on the same image plane comprises a diverging element for causing a second light ray to diverge relative to a first light ray, a converging element provided on the object side of the diverging element for converging the second light ray relative to the first light ray, and an objective lens provided on the object side of the two elements for converging both of the first light ray and the second light ray. The objective lens is disposed so that the point of intersection between the first light ray and the second light ray in the composite system comprising the diverging element and the converging element is coincident with the focal plane of the objective lens which is adjacent to the converging element.

Abstract: A variable magnification observation apparatus capable of changing the magnification thereof includes an optical fiber having an exit surface for emitting an illuminating light beam at an angle corresponding to a predetermined numerical aperture, an aperture stop member disposed near the exit surface of the optical fiber, a field stop member disposed at a predetermined distance from the aperture stop member, and a negative lens removably inserted in the optical path between the aperture stop member and the field stop member.