PURPOSE: To obtain the optical system which has neither a deficiency in lightness on a far-point side nor deterioration in resolving power and is improved in subject field depth on a near-point side by arranging an optical element which generates a positive spherical aberration nearby the pupil position of an optical system.
CONSTITUTION: The optical system is equipped with an objective O, relay lenses R1-R3, an ocular E, and an adapter lens. An spherical lens which has an spherical surface r43 for generating the spherical aberration of the whole system in the positive direction is provided nearby the eye point of the optical system. A positive spherical aberration is generated by this spherical lens to provide the spherical aberration of the whole system even in the direction of overcorrection. If an spherical surface lens (near-point shift lens) that uses only spherical surface coefficients of 4th order and 6th order is adopted as the spherical surface shape, then only the spherical aberration can be generated without varying the near axis quantity of the whole system, which is preferable.
HASEGAWA AKIRA
TAKAYAMA TOSHIICHI
SUZUKI TAKAYUKI
MATSUMOTO SHINYA
