A projector includes a light source module, a light valve, and a projection lens. The light source module is adapted to provide an illumination light beam and includes a base having first and second side surfaces, first and second color light-emitting units respectively disposed on the first and second side surfaces, and first and second heat dissipation structures respectively connected to the first and second color light-emitting units. The first and second heat dissipation structures are separated from each other and define an accommodation space together. The light valve is located on a transmission path of the illumination light beam and adapted to convert the illumination light beam into an image light beam. The projection lens is located on a transmission path of the image light beam and adapted to project the image light beam.

An optical system includes, in order from an object side to an image side, a first lens unit having a negative refractive power, a first reflective member, a second lens unit including an aperture diaphragm and having a positive refractive power, a second reflective member, and a third lens unit having a positive refractive power. Following inequalities are satisfied:

−1.27<(f1/f)/Npr<−0.70

0.60<f2/f3<1.60

where f represents a focal length of the optical system, f1 represents a focal length of the first lens unit, f2 represents a focal length of the second lens unit, f3 represents a focal length of the third lens unit, and NPr represents a refractive index of the first reflective member.

An optical system includes, in order from an object side to an image side, a first lens unit having a negative refractive power, a first reflective member, a second lens unit including an aperture diaphragm and having a positive refractive power, a second reflective member, and a third lens unit having a positive refractive power. Following inequalities are satisfied:

−1.27<(f1/f)/Npr<−0.70

0.60<f2/f3<1.60

where f represents a focal length of the optical system, f1 represents a focal length of the first lens unit, f2 represents a focal length of the second lens unit, f3 represents a focal length of the third lens unit, and NPr represents a refractive index of the first reflective member.

An optical lens assembly, including a first lens element, a second lens element, a third lens element, a fourth lens element, and a fifth lens element sequentially along an optical axis from a first side to a second side, is provided. The optical lens assembly satisfies the conditional expression of D34/D12≥2.600. Furthermore, other optical lens assemblies are also provided.

An optical lens assembly, including a first lens element, a second lens element, a third lens element, a fourth lens element, and a fifth lens element sequentially along an optical axis from a first side to a second side, is provided. The optical lens assembly satisfies the conditional expression of D34/D12≥2.600. Furthermore, other optical lens assemblies are also provided.

An image sensor includes imaging pixels and a patterned liquid crystal polarizer (LCP). The imaging pixel include subpixels. The patterned LCP is disposed over the subpixels and configured to direct a particular polarized portion of imaging light to particular subpixels.

An optical system includes a first optical subsystem disposed on an enlargement side and a second optical subsystem disposed on a reduction side with an intermediate image in between. The first optical subsystem includes: a first lens group that is disposed on the enlargement side of a first stop with a first distance, in which other lenses could be disposed but no other lenses are disposed, and is provided on the enlargement side with a first component with negative refractive power; and a second lens group that has positive refractive power, is disposed on the reduction side of the first stop with a second distance, in which other lenses could be disposed but no lenses are disposed, and forms the intermediate image so as to be adjacent on a reduction side of the second lens group and so as to be tilted toward the enlargement side.

A projection apparatus includes a display element that displays an image, a projection optical system that forms a projection image by projecting the image, an imaging unit that includes an imaging optical system which images a first region including an optical axis of the projection optical system in the projection image, and an imaging element which captures an image formed by the imaging optical system, and a processor that controls focus adjustment on a second region not including the optical axis in the projection image based on information acquired from the imaging unit, in which a position of the projection image is changeable by changing a relative position between at least a part of the projection optical system and the display element, and a predetermined conditional expression is satisfied.

A projection optical system includes a first lens group having negative power, a second lens group having positive power and disposed at a reduction side of the first lens group, and a third lens group having positive power and disposed at the reduction side of the second lens group. The first lens group includes at least three negative lenses. The second lens group includes at least one positive lens. The third lens group includes a plurality of positive lenses. The at least three negative lenses of the first lens group are each a single lens. The third lens group includes a jointed lens including at least one of the plurality of positive lenses. NA is a reduction-side numerical aperture, Dst is a distortion aberration at a reduction-side maximum image height, and the projection optical system satisfies Conditional Expressions (1) and (2),
0.2<NA  (1)
−45%<Dst<−10%  (2).

A projection optical system includes a first lens group having negative power, a second lens group having positive power and disposed at a reduction side of the first lens group, and a third lens group having positive power and disposed at the reduction side of the second lens group. The first lens group includes at least three negative lenses. The second lens group includes at least one positive lens. The third lens group includes a plurality of positive lenses. The at least three negative lenses of the first lens group are each a single lens. The third lens group includes a jointed lens including at least one of the plurality of positive lenses. NA is a reduction-side numerical aperture, Dst is a distortion aberration at a reduction-side maximum image height, and the projection optical system satisfies Conditional Expressions (1) and (2),
0.2<NA  (1)
−45%<Dst<−10%  (2).