Variable power projecting device

摘要

A projecting device for projecting an image of the surface of a body on a light receiving surface, in which optical element blocks are provided symmetrically with respect to a stop, of which the diameter of aperture is always constant in varying the magnification. The device includes a projecting optical system to change the focal length by symmetrically moving with respect to the stop at least a part or the whole of the optical element blocks, and means for restricting the field of the surface of a body, disposed between said projecting optical system and the surface of the body. The exposure amount on the light receiving surface is maintained substantially constant in varying the magnification by making the change of the focussing magnification of the projecting optical system to mainly correspond with the change of refractive power of the optical element blocks which are disposed on both sides of said stop.