A projection lens includes, in order from a magnification side to a reduction side, a first lens group having a negative refractive power, a reflector to bend an optical path, a second lens group having a positive refractive power, and an aperture stop disposed within the second lens group. The second lens group has a positive refractive power on the magnification side of the aperture stop, and a negative refractive power on the reduction side of the aperture stop. Conditional formula (A) is satisfied: (A) Ot/Y′<6.1, where Ot is a distance along the optical axis between a maximum-magnification-side surface of the first lens group and a surface of a lens adjacent to a reduction-side surface of the reflector, and Y′ is a maximum height of the image displayed on the display surface of the image display element.

A projection optical system that projects, while enlarging, an image displayed on an image display surface includes in order from an enlargement side: a first negative refractive power lens group; a second negative refractive power lens group; at least one positive or negative refractive power lens group; a stop; and a first positive refractive power lens group. The projection optical system causes magnification variation by varying distances between lens groups. The at least one positive or negative refractive power lens groups disposed between the second negative refractive power lens group and the stop is movable during the magnification variation. The first positive refractive power lens group is an only lens group that is positioned closer to a reduction side than the stop and is also movable during the magnification variation.

There is provided an imaging lens with high-resolution which satisfies demand of wide field of view, low-profileness and low F-number in well balance, and excellently corrects aberrations. An imaging lens comprises, in order from an object side to an image side, a first lens, a second lens having negative refractive power near the optical axis, a third lens having a convex surface facing the image side near the optical axis, a fourth lens and a fifth lens, wherein said first lens has negative refractive power near the optical axis, an image-side surface of said fifth lens has a convex surface facing the image side near the optical axis, and below conditional expressions are satisfied:
3.00<(T4/f)×100<5.90
0.40<f2/f5<1.45
where
T4: a distance along the optical axis from the image-side surface of the fourth lens to the object-side surface of the fifth lens,
f: a focal length of the overall optical system of the imaging lens,
f2: a focal length of the second lens,
f5: a focal length of the fifth lens.

A projection optical system that projects, while enlarging, an image displayed on an image display surface includes in order from an enlargement side: a first negative refractive power lens group; a second negative refractive power lens group; at least one positive or negative refractive power lens group; a stop; and a first positive refractive power lens group. The projection optical system causes magnification variation by varying distances between lens groups. The at least one positive or negative refractive power lens groups disposed between the second negative refractive power lens group and the stop is movable during the magnification variation. The first positive refractive power lens group is an only lens group that is positioned closer to a reduction side than the stop and is also movable during the magnification variation.

There is provided an imaging lens with high-resolution which satisfies demand of wide field of view, low-profileness and low F-number in well balance, and excellently corrects aberrations. An imaging lens comprises, in order from an object side to an image side, a first lens, a second lens having negative refractive power near the optical axis, a third lens having a convex surface facing the image side near the optical axis, a fourth lens and a fifth lens, wherein said first lens has negative refractive power near the optical axis, an image-side surface of said fifth lens has a convex surface facing the image side near the optical axis, and below conditional expressions are satisfied:

3.00<(T4/f)100<5.90

0.40<f2/f5<1.45

where
T4: a distance along the optical axis from the image-side surface of the fourth lens to the object-side surface of the fifth lens,
f: a focal length of the overall optical system of the imaging lens,
f2: a focal length of the second lens,
f5: a focal length of the fifth lens.

A zoom lens includes, in order from an object side to an image side: a negative first lens unit; a negative second lens unit; and a positive third lens unit, in which the first lens unit is not moved for zooming, the second lens unit and the third lens unit are moved during zooming, and an interval between each pair of adjacent lens units is changed during zooming, in which the first lens unit includes at least two negative lenses, and a focal length of the first lens unit, a focal length of the zoom lens at a wide angle end, a focal length of the zoom lens at a telephoto end, an interval on an optical axis between the first lens unit and the second lens unit at the wide angle end, and a back focus at the wide angle end are appropriately set.

A projection zoom lens constituting a projection optical system of a projector, which projects an image displayed on a surface of an image display element on a projected surface, so as to magnify and display the image includes, in order from the projected surface side to the image display element side, a first lens group having a negative refractive power, a second lens group having a negative refractive power, a third lens group having a positive refractive power, a fourth lens group having a positive refractive power, and a fifth lens group, wherein a refractive power of the fifth lens group is weaker than the refractive power of the first lens group, the refractive power of the second lens group, the refractive power of the third lens group, and the refractive power of the fourth lens group.

A projection zoom lens constituting a projection optical system of a projector, which projects an image displayed on a surface of an image display element on a projected surface, so as to magnify and display the image includes, in order from the projected surface side to the image display element side, a first lens group having a negative refractive power, a second lens group having a negative refractive power, a third lens group having a positive refractive power, a fourth lens group having a positive refractive power, and a fifth lens group, wherein a refractive power of the fifth lens group is weaker than the refractive power of the first lens group, the refractive power of the second lens group, the refractive power of the third lens group, and the refractive power of the fourth lens group.

Disclosed is a projection zoom lens used in an image display device configured to project an image onto a target projection surface and display a magnified image of the image, in which the projection zoom lens has a five-lens-group configuration in which first to fifth lens groups G1 to G5 are arranged from the magnification side toward the reduction side, and each of the constituent lens groups or lenses included in the lens groups has a combination of negative and positive refractive powers, and in the lens configuration, focal lengths of the constituent lens groups, relative travel distances, lens distances to the image display element, and constituent lens shapes are properly selected.

Disclosed is a projection zoom lens used in an image display device configured to project an image onto a target projection surface and display a magnified image of the image, in which the projection zoom lens has a five-lens-group configuration in which first to fifth lens groups G1 to G5 are arranged from the magnification side toward the reduction side, and each of the constituent lens groups or lenses included in the lens groups has a combination of negative and positive refractive powers, and in the lens configuration, focal lengths of the constituent lens groups, relative travel distances, lens distances to the image display element, and constituent lens shapes are properly selected.