Optical filter and optical system, image pickup apparatus, and lens apparatus which include the same

An optical filter having a region where a transmittance changes in a first direction, the optical filter comprising:

• a substrate;
• a phase compensation layer;
• and
• a first layer,
• the substrate, the phase compensation layer, and the first layer being arranged in this order along a second direction orthogonal to the first direction,
• wherein a thickness of the first layer changes in the first direction,
• wherein a thickness of the phase compensation layer increases in a direction opposite to an increasing direction of the thickness of the first layer,
• wherein a conditional expression below is satisfied:
• 0<k≤0.5,
• where k is an extinction coefficient of the first layer, and
• wherein the thickness of the phase compensation layer changes to satisfy a conditional expression below for light having a wavelength of 550 nm:
• |OPD/λ|≤0.3
• where λ is a wavelength of light and OPD is an optical path difference between positions where the thickness of the first layer is minimized and maximized.

An optical system comprising a plurality of optical elements including an optical filter, the optical filter having a region where a transmittance changes in a first direction, the optical filter including:

• a substrates;
• a first layer;
• and
• a second layer,
• the substrate, the first layer, and the second layer being arranged in this order along a second direction orthogonal to the first direction,
• wherein a thickness of the first layer in the second direction changes in the first direction, and
• wherein conditional expressions below are satisfied:
• 0.05≤k≤0.35, and
• |Re(ηsub)/Y0−Nabs|<0.25,
• where k is an extinction coefficient of the first layer, ηsub is an equivalent admittance from air to the second layer for light of 550 nm, Y0 is an admittance in a free space, and Nabs is a refractive index of the first layer for light of 550 nm.

An optical filter having a region where a transmittance changes in a first direction, the optical filter comprising;

• a substrate;
• an intermediate layer;
• and
• a first layer,
• the substrate, the intermediate layer, and the first layer being arranged in this order along a second direction orthogonal to the first direction,
• wherein a thickness of the first layer in the second direction changes in the first direction, and
• wherein conditional expressions below are satisfied:
• 0.05≤k≤0.35, and
• |Re(ηair)/Y0−Nabs|<0.25,
• where k is an extinction coefficient of the first layer, ηair is an equivalent admittance from the substrate to the intermediate layer for light of 550 nm, Y0 is an admittance in a free space, and Nabs is a refractive index of the first layer for light of 550 nm.