Objective optical system, image pickup apparatus, and endoscope

An image pickup apparatus comprising a predetermined lens disposed near a pupil of an objective optical system, wherein

• the predetermined lens has a first refractive region including an optical axis and a second refractive region located outside the first refractive region,
• a refractive power of the second refractive region is greater than a refractive power of the first refractive region,
• a light beam reaching an image plane includes a first light beam and a second light beam,
• the first light beam is a light beam transmitted through the first refractive region and includes at least one or both of a beam of white light and a beam of near-infrared light,
• the second light beam is a light beam transmitted through the second refractive region and includes only the beam of near-infrared light, and
• the following Conditional Expression (1) is satisfied:
• 0
• <
• {
• (
• Dir
• /
• Dw
• )
• 2
• ×
• (
• Tir
• /
• Dir
• )
• }
• /
• {
• (
• fir
• -
• fe
• )
• /
• (
• Pich
• ×
• Fno
• )
• }
• <
• 0.1
• (
• 1
• )
• where Dir is an aperture diameter that allows the near-infrared light to pass through,
• Dw is an aperture diameter that allows the white light to pass through,
• Tir is a spherical segment amount in the second refractive region,
• fir is a focal length of the objective optical system at a predetermined wavelength,
• fe is a focal length of the objective optical system at e-line,
• Fno is an F-number of the objective optical system at e-line,
• Pich is a pixel pitch of an imager, wherein
• the spherical segment amount is a maximum distance among distances between a virtual plane and the second refractive region,
• the virtual plane is a plane passing through a boundary between the first refractive region and the second refractive region and being orthogonal to the optical axis,
• the distance is a distance in a direction parallel to the optical axis, and
• the predetermined wavelength is 835 nm.