Optical system and imaging apparatus including the same

An optical system comprising, in order from an object side to an image side:

• a front group with positive refractive power;
• an aperture stop;
• and
• a rear group with positive refractive power,
• wherein the front group includes, in order from the object side to the image side, a first lens with negative refractive power, a second lens with negative refractive power, a third lens, and a fourth lens with positive refractive power,
• wherein the rear group includes a cemented lens and a meniscus lens disposed closest to an image plane,
• wherein at least one of an object-side surface and an image-side surface of the meniscus lens is an aspherical surface,
• wherein a spherical surface passing through both edge portions in an effective region of the object-side surface has a concave shape toward the object side in a cross-section including an optical axis, and
• wherein the following inequality is satisfied:
• 0.80≤Rd≤1.00,
• where Rd is a value of a ratio of a diameter of a portion that has positive power in an effective region of the image-side surface to a diameter of the effective region of the image-side surface in a direction perpendicular to the optical axis.