Optical system, image projection apparatus, and imaging apparatus

An optical system internally having an intermediate imaging position MI that is conjugated to a magnification conjugate point on a magnification side and a reduction conjugate point on a reduction side, respectively, the optical system including:

• a magnification optical system having A (A is an integer of three or more) pieces of lens elements, positioned on the magnification side with respect to the intermediate imaging position;
• and
• a relay optical system having B (β is an integer of two or more) pieces of lens elements, positioned on the reduction side with respect to the intermediate imaging position MI,
• wherein a first lens group composed of β pieces (β is one or more and less than B) of lens elements positioned first from the magnification side in the relay optical system has a negative power,
• wherein the first lens group is fixed during zooming, and
• wherein the magnification optical system has a second focus lens group that corrects field curvature aberration by moving along the optical axis after focusing.

An optical system internally having an intermediate imaging position MI that is conjugated to a magnification conjugate point on a magnification side and a reduction conjugate point on a reduction side, respectively, the optical system including:

• a magnification optical system having A (A is an integer of three or more) pieces of lens elements, positioned on the magnification side with respect to the intermediate imaging position;
• and
• a relay optical system having B (B is an integer of two or more) pieces of lens elements, positioned on the reduction side with respect to the intermediate imaging position MI,
• wherein a first lens group composed of β pieces (β is one or more and less than B) of lens elements positioned first from the magnification side in the relay optical system has a negative power,
• wherein the relay optical system is fixed during focusing, and a part or all of the lens elements in the magnification optical system move along the optical axis during focusing, and
• wherein the magnification optical system has a second focus lens group that corrects field curvature aberration by moving along the optical axis after focusing.