Objective optical system and endoscope apparatus using the same

An objective optical system, comprising:

• a lens group which forms an image of an object;
• and
• an optical-path splitting element which is disposed on an image side of the lens group,
• wherein:
• the optical-path splitting element is disposed on an optical path of the lens group,
• the optical-path splitting element has an optical-path splitting surface which forms a first optical path and a second optical path,
• the first optical path is formed on an extended line of the optical path of the lens group,
• the second optical path is formed to intersect the first optical path,
• an optical image on the first optical path and an optical image on the second optical path are formed on a same plane,
• a reflecting surface is positioned in the second optical path,
• a predetermined optical surface is positioned in only the second optical path,
• a wavelength band of light transmitted through the predetermined optical surface or a wavelength band of light reflected at the predetermined optical surface is restricted,
• the wavelength band which is restricted is narrower than a wavelength band of light that travels along the other first optical path,
• a quarter-wave plate is positioned between the optical-path splitting surface and the reflecting surface,
• the optical-path splitting surface has a characteristic of transmitting P-polarized light and reflecting S-polarized light,
• the predetermined optical surface is positioned between the optical-path splitting surface and the quarter-wave plate,
• the predetermined optical surface is provided with an optical film,
• the optical film has spectral characteristics of generating light of the restricted wavelength band, and
• the following conditional expression (1) is satisfied:
• 3 nm≤Tλ×Δλ≤60 nm expression (1)
• where,
• Tλ denotes the maximum transmittance 0≤Tλ≤1.0 in the restricted wavelength band, and
• Δλ denotes a full width at half maximum of the restricted wavelength band.