Optical system and image pickup apparatus

An image pickup apparatus comprising:

• an optical system;
• and
• an image sensor configured to capture an image of an object through the optical system,
• wherein the optical system includes:
• a front group;
• an aperture stop configured to determine an on-axis light beam;
• and
• a rear group,
• wherein the front group includes a negative lens, and a first positive lens disposed on an image side of the negative lens,
• wherein the rear group includes at least two positive lenses, and
• wherein the following inequalities are satisfied:
• 0
• .
• 1
• ⁢
• 0
• ≤
• ST
• /
• TTL
• ≤
• 0
• .50
• 30
• ≤
• ❘
• "\[LeftBracketingBar]"
• fA
• /
• f
• ❘
• "\[RightBracketingBar]"
• 0.01
• ≤
• Bf
• /
• f
• ≤
• 1.
• 2
• where ST is a distance on an optical axis between a lens surface on the image side of a lens adjacent to and disposed on the object side of the aperture stop and a lens surface on the object side of a lens adjacent to and disposed on the image side of the aperture stop, TTL is an air equivalent value of a distance on the optical axis from a lens surface closest to the object of the optical system to an image plane, Bf is an air equivalent value of a distance on the optical axis from a lens surface closest to the image plane to the image plane, f is a focal length of the optical system, and fA is a focal length of the front group.