Image projection apparatus

1. An image projection apparatus comprising:

a light source configured to emit light;

an image display element configured to reflect the light emitted from the light source, the image display element including:

multiple micromirrors each having a reflecting surface, the multiple micromirrors arranged in two dimensions and forming an image display plane, each micromirror configured to change an angle of the reflecting surface with respect to the image display plane to change a direction of the light reflected by the reflecting surface; and

a projection optical system configured to project the light reflected from the image display element onto a projection surface as a projection image,

wherein conditional expressions (1) and (2) below are satisfied:

θ1≥14(deg)  (1)

1.2< BF/L< 2.2  (2)

where θ1 is a maximum tilt angle of the reflecting surface of each micromirror with respect to the image display plane, L is a diagonal length of the image display plane, and BF is a distance between a vertex of a lens within the projection optical system and closest to the image display plane and the image display plane along an optical axis of the projection optical system,

wherein conditional expression (3) below is satisfied:

( D/ 2− ImC )/ BF< 0.2  (3)

where D is an outer diameter of the lens within the projection optical system and closest to the image display plane, and ImC is a distance from an intersection point of the optical axis and a plane including the image display plane to a point farthest from the intersection point within the image display plane.

2. The image projection apparatus according to claim 1 ,

wherein the projection optical system is a telecentric lens.

3. The image projection apparatus according to claim 1 ,

wherein the projection optical system includes an aperture stop and a field stop, the field stop is closer to the image display element than the aperture stop.

4. The image projection apparatus according to claim 1 ,

wherein the projection optical system further includes:

a holder holding a lens group within the projection optical system and closest to the image display element; and

a light shield on the holder, the light shield configured to absorb light.

5. The image projection apparatus according to claim 1 ,

wherein a center of the image display plane of the image display element is offset from an extended line of the optical axis of the projection optical system.

6. An image projection apparatus comprising:

a light source configured to emit light;

an image display element configured to reflect the light emitted from the light source, the image display element including:

multiple micromirrors each having a reflecting surface, the multiple micromirrors arranged in two dimensions and forming an image display plane, each micromirror configured to change an angle of the reflecting surface with respect to the image display plane to change a direction of the light reflected by the reflecting surface; and

a projection optical system configured to project the light reflected from the image display element onto a projection surface as a projection image,

wherein conditional expressions (1) and (2) below are satisfied:

θ1≥14(deg)  (1)

1.2< BF/L< 2.2  (2)

where θ1 is a maximum tilt angle of the reflecting surface of each micromirror with respect to the image display plane, L is a diagonal length of the image display plane, and BF is a distance between a vertex of a lens within the projection optical system and closest to the image display plane and the image display plane along an optical axis of the projection optical system,

the image projection apparatus further comprising multiple optical elements between the projection optical system and the image display element,

wherein conditional expression (4) below is satisfied:

T/BF< 0.7  (4)

where T is a total thickness of the multiple optical elements.

7. The image projection apparatus according to claim 6 ,

wherein the multiple optical elements include at least one parallel flat plate configured to tilt with respect to the optical axis.

8. An image projection apparatus comprising:

a light source configured to emit light;

an image display element configured to reflect the light emitted from the light source, the image display element including:

multiple micromirrors each having a reflecting surface, the multiple micromirrors arranged in two dimensions and forming an image display plane, each micromirror configured to change an angle of the reflecting surface with respect to the image display plane to change a direction of the light reflected by the reflecting surface; and

a projection optical system configured to project the light reflected from the image display element onto a projection surface as a projection image,

wherein conditional expressions (1) and (2) below are satisfied:

θ1≥14(deg)  (1)

1.2< BF/L< 2.2  (2)

where θ1 is a maximum tilt angle of the reflecting surface of each micromirror with respect to the image display plane, L is a diagonal length of the image display plane, and BF is a distance between a vertex of a lens within the projection optical system and closest to the image display plane and the image display plane along an optical axis of the projection optical system,

wherein conditional expression (5) below is satisfied:

Et< 35( m 2 ·sr )  (5)

where Et is an etendue defined by equation (6) below:

Et=M ×π×NA 2   (6)

where M is an area of the image display plane, and NA is a numerical aperture of the projection optical system.