Optical system, image pickup apparatus, and lens apparatus

An image pickup apparatus comprising:

• an optical system;
• and
• an image sensor configured to receive an image formed by the optical system,
• wherein the optical system includes, in order from an object side to an image side, a front unit having negative refractive power, an aperture stop, and a rear unit having positive refractive power,
• wherein the front unit includes a plurality of aspheric lenses, and
• wherein the following inequality is satisfied:
• 0.05<x1/f<0.50
• where T is a distance on an optical axis from a surface vertex of an aspheric surface on the object side of each of the plurality of aspheric lenses to the aperture stop, EA is an effective diameter of the aspheric surface, x1 is a distance in an optical axis direction between a position on a reference spherical surface, which is defined as a spherical surface passing a position on the aspheric surface distant from the optical axis by a distance of T/2 in a direction orthogonal to the optical axis and the surface vertex, distant from the optical axis by a distance of EA/2 in the direction orthogonal to the optical axis and a position on the aspheric surface distant from the optical axis by the distance of EA/2 in the direction orthogonal to the optical axis, and f is a focal length of the optical system.

A lens apparatus comprising:

• an optical system;
• and
• an operation unit operable by a user,
• wherein the optical system includes, in order from an object side to an image side, a front unit having negative refractive power, an aperture stop, and a rear unit having positive refractive power,
• wherein the front unit includes a plurality of aspheric lenses, and
• wherein the following inequality is satisfied:
• 0.05<x1/f<0.50
• where T is a distance on an optical axis from a surface vertex of an aspheric surface on the object side of each of the plurality of aspheric lenses to the aperture stop, EA is an effective diameter of the aspheric surface, x1 is a distance in an optical axis direction between a position on a reference spherical surface, which is defined as a spherical surface passing a position on the aspheric surface distant from the optical axis by a distance of T/2 in a direction orthogonal to the optical axis and the surface vertex, distant from the optical axis by a distance of EA/2 in the direction orthogonal to the optical axis and a position on the aspheric surface distant from the optical axis by the distance of EA/2 in the direction orthogonal to the optical axis, and f is a focal length of the optical system.