Image projection optical system and image projection apparatus

An image projection optical system comprising:

• an optical element into which light from an image-forming element forming an original image enters;
• and
• a zoom lens magnifying and projecting the light from the optical element onto a projection surface,
• wherein the optical element satisfies the following condition (1),
• wherein the zoom lens includes, in order from a magnification side, a first lens unit, a second lens unit, and a plurality of lens units disposed closer to a reduction side than the second lens unit,
• wherein, the first lens unit is a negative lens unit,
• wherein the plurality of lens units disposed closer to the reduction side than the second lens unit satisfies the following condition (2),
• wherein magnification-side positive lens elements disposed closer to the magnification side than a negative lens element whose effective diameter is smallest in the plurality of lens units disposed closer to the reduction side than the second lens unit satisfy the following condition (3), and
• wherein reduction-side positive lens elements disposed closer to the reduction side than the negative lens element whose effective diameter is smallest satisfy the following condition (4):
• Σ(Di×Ndi)/fw>4.0 (1)
• |dn/dt|<1.0×10−5 (2)
• where Di represents a length of the optical element along an optical path from the image-forming element toward the zoom lens, Ndi represents a refractive index of a material forming the optical element for a d-line, fw represents a focal length of the zoom lens at a wide-angle end, and dn/dt represents a change amount of a refractive index of a material forming each of the plurality of lens units disposed closer to the reduction side than the second lens unit for the d-line, the refractive index change being caused by a temperature change from 25° C.,
• {9.0×Σ(1/fpA)+5.0×Σ(1/fpB)+0.5×Σ(1/fpC)}/Σ(1/fp) <1 (3)
• {9.0×Σ(1/fpA)+0.3×Σ(1/fpB)+2.0×Σ(1/fpC)}/Σ(1/fp) <1 (4)
• where fpA, fpB, and fpC represent focal lengths of the magnification-side positive lens elements or the reduction-side positive lens elements, whose materials are respectively included in an A-region of an Abbe number νd of νd>75, a B-region of 68<νd<75, and a C-region of 68>νd, and fp represents an entire focal length of all the magnification-side positive lens elements or all the reduction-side positive lens elements, whose materials are included in the A-region, the B-region, and the C-region.