| 摘要 |
An optical system for an endoscope can be used by being disposed in the distal end portion of the endoscope, the optical system having a plurality of illumination optical systems, which allow light emitted from a light source to diverge, and an observation optical system, in which at least one of the plurality of illumination optical systems satisfies the following formula (1): <?in-line-formulae description="In-line Formulae" end="lead"?>0<=-df(theta)/dtheta<=0.025, 10°<=theta<=85° (1),<?in-line-formulae description="In-line Formulae" end="tail"?> wherein theta denotes an angle of emission from a center of the illumination optical system, and f(theta) denotes a value obtained by standardizing, at an illuminance at a time when the angle theta of emission is 0°, an illuminance distribution (spherical light distribution characteristics) at a time when a spherical object is illuminated by the illumination optical system.
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