Optical system and image pickup apparatus having the same

An image pickup apparatus comprising:

• an optical system;
• and
• an image sensor configured to receive an image light formed by the optical system,
• wherein the optical system includes, in order from an object side to an image side, a front group, an aperture stop, and a rear group that has positive refractive power as a whole,
• wherein the front group includes a first lens having negative refractive power disposed closest to an object,
• wherein the rear group includes a final lens having positive refractive power disposed closest to an image plane,
• wherein the optical system includes four or more lenses disposed between the first lens and the final lens,
• wherein a lens surface near an optical axis of the final lens has a meniscus shape with a convex surface on the object side, and
• wherein the following inequalities are satisfied:
• 0.1<TTL/(f×tan ω))<4.0
• 1.50<PNdave<2.00
• 0.2<sk/TTL<1.0
• where f is a focal length of the optical system, ω (°) is a half angle of view of the optical system, sk is a back focus of the optical system, TTL is a length acquired by adding the back focus to a distance on an optical axis from a lens surface closest to the object of the optical system to a lens surface closest to an image plane of the optical system, and PNdave is an average value of refractive indices for d-line of materials of all positive lenses included in the optical system.