Wide-angle optical system and image pickup apparatus using the same

A wide-angle optical system having a lens component which has a plurality of optical surfaces, and in the lens component, two optical surfaces are in contact with air, and at least one optical surface is a curved surface, comprising in order from an object side:

• a first lens unit having a negative refractive power;
• a second lens unit having a positive refractive power;
• and
• a third lens unit having a positive refractive power, wherein
• at the time of carrying out a focal-position adjustment from a far point to a near point, the second lens unit is moved from a first position toward a second position, the first position is a position at which a distance between the first lens unit and the second lens unit becomes the minimum, and the second position is a position at which a distance between the second lens unit and the third lens unit becomes the minimum,
• the third lens unit includes not less than three lens components,
• not less than three lens components include a first lens component and a second lens component, and the first lens component is a lens component located nearest to an object, in the third lens unit, and the second lens component is a lens component located second from the object side in the third lens unit,
• the first lens component is a single lens and the second lens component is a cemented lens, and
• following conditional expression (1) is satisfied
• −0.60<(n2C′−n2C)/r2C<−0.05 (1)
• where,
• n2C denotes a refractive index for a d-line of a medium located on the object side of a cemented surface of the second lens component,
• n2C′ denotes a refractive index for the d-line of a medium located on an image side of the cemented surface of the second lens component, and
• r2C denotes a radius of curvature of the cemented surface.