Imaging optical system, image projection optical system and image projection apparatus

An image projection apparatus comprising:

• an image projection optical system comprising:
• a light modulation element configured to modulate an entering light;
• and
• an imaging optical system which is a projection optical system configured to project, onto a projection surface disposed on a magnification conjugate side further than the imaging optical system, a light modulated by the light modulation element disposed on a reduction conjugate side further than the imaging optical system,
• wherein the imaging optical system is configured to make a predetermined position on the magnification conjugate side and another predetermined position on the reduction conjugate side conjugate to each other and to form an intermediate image conjugate to both the predetermined positions, the imaging optical system comprising:
• a magnification side positive lens disposed on the magnification conjugate side further than an intermediate imaging position where the intermediate image is formed and being convex toward the magnification conjugate side, the intermediate imaging position being located between two points at both of which an off-axis principal ray of a light flux entering the imaging optical system intersects with an optical axis of the imaging optical system;
• a reduction side positive lens disposed between the two points and on the reduction conjugate side further than the intermediate imaging position and being convex toward the reduction conjugate side;
• and
• a negative lens disposed between the magnification side positive lens and the reduction side positive lens, wherein the negative lens includes a plurality of lenses and one lens of the plurality of lenses is a particular negative lens disposed closest to the intermediate imaging position, the particular negative lens having a negative power,
• wherein:
• when the magnification side positive lens, the particular negative lens, and the reduction side positive lens are referred to as a first lens, a second lens and a third lens, respectively, the following conditions are satisfied:
• 5<ν2−ν1<80
• 5<ν2−ν3<80
• 0<ν3−ν1<20
• 0.03<N1−N2<1.0
• 0.03<N3−N2<1.0
• where ν1 represents an Abbe number of a material of the first lens, ν2 represents an Abbe number of a material of the second lens, ν3 represents an Abbe number of a material of the third lens, N1 represents a refractive index of the material of the first lens, N2 represents a refractive index of the material of the second lens, and N3 represents a refractive index of the material of the third lens.

An imaging optical system configured to make a predetermined position on a magnification conjugate side and another predetermined position on a reduction conjugate side conjugate to each other and to form an intermediate image at an intermediate imaging position which is conjugate to both the predetermined positions and which is located between two points at both of which an off-axis principal ray of a light flux entering the optical system intersects with an optical axis of the optical system, the optical system comprising:

• a first positive lens disposed between the two points and on the magnification conjugate side further than the intermediate imaging position and being convex toward the magnification conjugate side;
• a second positive lens disposed between the two points and on the reduction conjugate side further than the intermediate imaging position and being convex toward the reduction conjugate side;
• and
• a first negative lens and a second negative lens disposed in order from the intermediate imaging position to the second positive lens,
• wherein the following conditions are satisfied:
• 5<ν2−ν1<80
• 5<ν2−ν3<80
• 0<ν3−ν1<20
• 0.03<N1−N2<1.0
• 0.03<N3−N2<1.0
• where ν1 represents an Abbe number of a material of the first positive lens, ν2 represents an Abbe number of a material of the first negative lens, ν3 represents an Abbe number of a material of the second positive lens, N1 represents a refractive index of the material of the first positive lens, N2 represents a refractive index of the material of the first negative lens, and N3 represents a refractive index of the material of the second positive lens.

An image projection apparatus comprising:

• an image projection optical system comprising:
• a light modulation element configured to modulate an entering light;
• and
• an imaging optical system which is a projection optical system configured to project, onto a projection surface disposed on a magnification conjugate side further than the imaging optical system, a light modulated by the light modulation element disposed on a reduction conjugate side further than the imaging optical system,
• wherein the imaging optical system is configured to make a predetermined position on the magnification conjugate side and another predetermined position on the reduction conjugate side conjugate to each other and to form an intermediate image at an intermediate imaging position which is conjugate to both the predetermined positions and which is located between two points at both of which an off-axis principal ray of a light flux entering the optical system intersects with an optical axis of the optical system, the imaging optical system comprising:
• a first positive lens disposed between the two points and on the magnification conjugate side further than the intermediate imaging position and being convex toward the magnification conjugate side;
• a second positive lens disposed between the two points and on the reduction conjugate side further than the intermediate imaging position and being convex toward the reduction conjugate side;
• and
• a first negative lens and a second negative lens disposed in order from the intermediate imaging position to the second positive lens,
• wherein the following conditions are satisfied:
• 5<ν2−ν1<80
• 5<ν2−ν3<80
• 0<ν3−ν1<20
• 0.03<N1−N2<1.0
• 0.03<N3−N2<1.0
• where ν1 represents an Abbe number of a material of the first positive lens, ν2 represents an Abbe number of a material of the first negative lens, ν3 represents an Abbe number of a material of the second positive lens, N1 represents a refractive index of the material of the first positive lens, N2 represents a refractive index of the material of the first negative lens, and N3 represents a refractive index of the material of the second positive lens.