Fresnel lens for projector
A projector includes a light source, a Fresnel lens group parallelizing the beam output from the light source, a light-incident-side polarizer transmitting the beam having exited out of the Fresnel lens group, a light modulator modulating the beam having passed through the light-incident-side polarizer to form a projection image, a light-exiting-side polarizer transmitting the beam modulated by the light modulator, and a projection lens projecting the beam having passed through the light-exiting-side polarizer. The Fresnel lens group includes a plurality of Fresnel lenses. The first Fresnel lens, which is disposed at a position closest to the light source in the Fresnel lens group, has positive power. The light incident surface of the first Fresnel lens does not have a Fresnel surface. The light exiting surface of the first Fresnel lens has a Fresnel surface.
1 . A projector comprising:
a light source;
a Fresnel lens group that parallelizes a beam output from the light source;
a light-incident-side polarizer that transmits the beam that exits out of the Fresnel lens group;
a light modulator that modulates the beam passing through the light-incident-side polarizer to form a projection image;
a light-exiting-side polarizer that transmits the beam modulated by the light modulator; and
a projection lens that projects the beam passing through the light-exiting-side polarizer,
wherein the Fresnel lens group includes a first Fresnel lens having positive power and disposed at a position closest to the light source in the Fresnel lens group, and a second Fresnel lens having positive power and disposed at a position shifted from the first Fresnel lens toward the light modulator,
a light incident surface of the first Fresnel lens does not have a Fresnel surface,
a light exiting surface of the first Fresnel lens has a Fresnel surface, and
an adjustment mechanism is configured to change an axial distance between the first Fresnel lens and the second Fresnel lens,
wherein
a light incident surface of the second Fresnel lens does not have a Fresnel surface, and
a light exiting surface of the second Fresnel lens has a Fresnel surface.
2 . The projector according to claim 1 ,
wherein a light incident surface of the second Fresnel lens has a Fresnel surface, and
a light exiting surface of the second Fresnel lens does not have a Fresnel surface.
3 . The projector according to claim 2 , wherein a focal length of the first Fresnel lens is shorter than a focal length of the second Fresnel lens.
4 . The projector according to claim 1 ,
wherein the Fresnel lens group includes a third Fresnel lens disposed at a position shifted from the second Fresnel lens toward the light modulator, and
the third Fresnel lens has positive power.
5 . The projector according to claim 1 , further comprising a polarization conversion optical system that is disposed between the light source and the Fresnel lens group and converts polarization directions of the beam output from the light source.
6 . The projector according to claim 5 , wherein the polarization conversion optical system includes a polarization beam splitter that directly transmits one linearly polarized light component out of polarized light components contained in the beam incident thereon and reflects another linearly polarized light component in a direction perpendicular to an optical axis, a total reflection mirror that reflects the other linearly polarized light component reflected off the polarization beam splitter in a direction parallel to the optical axis, and a retardation film that converts the other linearly polarized light component reflected off the total reflection mirror into the one linearly polarized light component.
7 . The projector according to claim 1 , further comprising a polarization conversion optical system that is disposed between the Fresnel lens group and the light-incident-side polarizer and converts polarization directions of the beam that exits out of the Fresnel lens group.
8 . A projector comprising:
a light source;
a Fresnel lens group that parallelizes a beam output from the light source;
a light-incident-side polarizer that transmits the beam that exits out of the Fresnel lens group;
a light modulator that modulates the beam passing through the light-incident-side polarizer to form a projection image;
a light-exiting-side polarizer that transmits the beam modulated by the light modulator; and
a projection lens that projects the beam passing through the light-exiting-side polarizer,
wherein the Fresnel lens group includes a first Fresnel lens having positive power and disposed at a position closest to the light source in the Fresnel lens group, and a second Fresnel lens having positive power and disposed at a position shifted from the first Fresnel lens toward the light modulator,
a light incident surface of the first Fresnel lens does not have a Fresnel surface,
a light exiting surface of the first Fresnel lens has a Fresnel surface, and
wherein
a light incident surface of the second Fresnel lens does not have a Fresnel surface,
a light exiting surface of the second Fresnel lens has a Fresnel surface
the Fresnel lens group includes a third Fresnel lens disposed at a position shifted from the second Fresnel lens toward the light modulator, and
the third Fresnel lens has positive power.
9 . The projector according to claim 8 ,
wherein a light incident surface of the second Fresnel lens has a Fresnel surface, and
a light exiting surface of the second Fresnel lens does not have a Fresnel surface.
10 . The projector according to claim 9 , wherein a focal length of the first Fresnel lens is shorter than a focal length of the second Fresnel lens.
11 . The projector according to claim 8 , further comprising an adjustment mechanism that changes an axial distance between the first Fresnel lens and the second Fresnel lens.
12 . The projector according to claim 8 , further comprising a polarization conversion optical system that is disposed between the light source and the Fresnel lens group and converts polarization directions of the beam output from the light source.
13 . The projector according to claim 12 , wherein the polarization conversion optical system includes a polarization beam splitter that directly transmits one linearly polarized light component out of polarized light components contained in the beam incident thereon and reflects another linearly polarized light component in a direction perpendicular to an optical axis, a total reflection mirror that reflects the other linearly polarized light component reflected off the polarization beam splitter in a direction parallel to the optical axis, and a retardation film that converts the other linearly polarized light component reflected off the total reflection mirror into the one linearly polarized light component.
14 . The projector according to claim 8 , further comprising a polarization conversion optical system that is disposed between the Fresnel lens group and the light-incident-side polarizer and converts polarization directions of the beam that exits out of the Fresnel lens group.
15 . A projector comprising:
a light source;
a Fresnel lens group that parallelizes a beam output from the light source;
a light-incident-side polarizer that transmits the beam that exits out of the Fresnel lens group;
a light modulator that modulates the beam passing through the light-incident-side polarizer to form a projection image;
a light-exiting-side polarizer that transmits the beam modulated by the light modulator;
a projection lens that projects the beam passing through the light-exiting-side polarizer, and
a polarization conversion optical system is disposed between the Fresnel lens group and the light-incident-side polarizer and converts polarization directions of the beam that exits out of the Fresnel lens group,
wherein the Fresnel lens group includes a first Fresnel lens having positive power and disposed at a position closest to the light source in the Fresnel lens group, and a second Fresnel lens having positive power and disposed at a position shifted from the first Fresnel lens toward the light modulator,
a light incident surface of the first Fresnel lens does not have a Fresnel surface, and
a light exiting surface of the first Fresnel lens has a Fresnel surface.
16 . The projector according to claim 15 ,
wherein a light incident surface of the second Fresnel lens does not have a Fresnel surface, and
a light exiting surface of the second Fresnel lens has a Fresnel surface.
17 . The projector according to claim 15 ,
wherein a light incident surface of the second Fresnel lens has a Fresnel surface, and
a light exiting surface of the second Fresnel lens does not have a Fresnel surface.
18 . The projector according to claim 15 , wherein a focal length of the first Fresnel lens is shorter than a focal length of the second Fresnel lens.
19 . The projector according to claim 15 , further comprising an adjustment mechanism that changes an axial distance between the first Fresnel lens and the second Fresnel lens.