Abstract: An imaging optical system having superior optical performance with the improved correction of chromatic aberration over a wide wavelength range extending from the visible wavelength range to the infrared wavelength range is provided. According to one aspect, an imaging optical system includes, in order from an object, a front lens group GF with a positive refractive power having at least one lens element, an aperture stop SP and a rear lens group GR with a positive refractive power having at least one lens element. The front lens group GF includes a double convex positive lens GT arranged to the most object side. At least one of the front lens group GF and the rear lens group GR includes a triple cemented lens GS being adjacent to the aperture stop SP having a negative refractive power as a whole composed of a first positive lens, a negative lens, and a second positive lens. Predetermined conditional expression is satisfied.

Abstract: An imaging optical system having superior optical performance with the improved correction of chromatic aberration over a wide wavelength range extending from the visible wavelength range to the infrared wavelength range is provided. According to one aspect, an imaging optical system includes, in order from an object, a front lens group GF with a positive refractive power having at least one lens element, an aperture stop SP and a rear lens group GR with a positive refractive power having at least one lens element. The front lens group GF includes a double convex positive lens GT arranged to the most object side. At least one of the front lens group GF and the rear lens group GR includes a triple cemented lens GS being adjacent to the aperture stop SP having a negative refractive power as a whole composed of a first positive lens, a negative lens, and a second positive lens. Predetermined conditional expression is satisfied.