Projection lens system and image projection apparatus

A projection lens system, comprising:

• a front group disposed on a projection-plane side;
• a rear group disposed on a display-surface side of an image display element inclined with reference to the projection plane;
• and
• an aperture stop disposed on the display-surface side with reference to the front group, wherein
• the front group having a front-group optical axis, the rear group having a rear-group optical axis parallel to the front-group optical axis, the front-group optical axis and the rear-group optical axis being shifted by an amount of shift Δ relative to each other, in a direction perpendicular to the front-group optical axis and the rear-group optical axis,
• the front-group optical axis and the rear-group optical axis being on a shared plane shared by a display-surface normal assumed on the display surface and a projection-plane normal line assumed on the projection plane to intersect with the display-surface normal,
• the rear-group optical axis being tilted on the shared plane at a tilt angle ξ with reference to the display-surface normal,
• when the amount of shift Δ is zero, the tilt angle ξ satisfies a first conditional expression as follows:
• 0<ξ/ξs<1,
• where ξs denotes a tilt angle when Scheimpflug principle is satisfied with reference to the display surface and the projection plane,
• assuming that a straight line connecting a center of the projection plane and a center of the display surface is a reference line, the rear-group optical axis is shifted in a direction perpendicular to the front-group optical axis, by an amount of shift Δ, where Δ≠0, with reference to a tilt-reference state where a common optical axis of the front group and the rear group is tilted around a point of intersection of the reference line and a lens surface of the front group on the projection-plane side by the tilt angle ξ with reference to a non-shifted reference state in which the common optical axis matches the reference line,
• the front-group optical axis and the rear-group optical axis are shifted as a whole in a direction perpendicular to the front-group optical axis while maintaining the tilt angle ξ and the amount of shift Δ,
• the front-group optical axis is shifted by an amount of shift Δ1 with reference to the rear-group optical axis, and
• a second conditional expression as follows is satisfied:
• 0.000047 (/mm)<|Δ1/f1|/f<0.001 (/mm), where
• f1 denotes focal length of the front group, and
• f denotes focal length of the front group and the rear group.

A projection lens system, comprising:

• a front group disposed on a projection-plane side;
• a rear group disposed on a display-surface side of an image display element inclined with reference to the projection plane;
• and
• an aperture stop disposed on the display-surface side with reference to the front group, wherein
• the front group having a front-group optical axis, the rear group having a rear-group optical axis parallel to the front-group optical axis, the front-group optical axis and the rear-group optical axis being shifted by an amount of shift Δ relative to each other, in a direction perpendicular to the front-group optical axis and the rear-group optical axis,
• the front-group optical axis and the rear-group optical axis being on a shared plane shared by a display-surface normal assumed on the display surface and a projection-plane normal line assumed on the projection plane to intersect with the display-surface normal,
• the rear-group optical axis being tilted on the shared plane at a tilt angle ξ with reference to the display-surface normal,
• when the amount of shift Δ is zero, the tilt angle ξ satisfies a first conditional expression as follows:
• 0<ξ/ξs<1,
• where ξs denotes a tilt angle when Scheimpflug principle is satisfied with reference to the display surface and the projection plane,
• assuming that a straight line connecting a center of the projection plane and a center of the display surface is a reference line, the rear-group optical axis is shifted in a direction perpendicular to the front-group optical axis, by an amount of shift Δ, where Δ≠0, with reference to a tilt-reference state where a common optical axis of the front group and the rear group is tilted around a point of intersection of the reference line and a lens surface of the front group on the projection-plane side by the tilt angle ξ with reference to a non-shifted reference state in which the common optical axis matches the reference line,
• the rear-group optical axis is shifted by an amount of shift Δ2 with reference to the front-group optical axis, and
• a second conditional expression as follows is satisfied:
• 0.000047 (/mm)<|Δ2/f2|/f<0.001 (/mm), where
• f2 denotes focal length of the rear group, and
• f denotes focal length of the front group and the rear group.

A projection lens system, comprising:

• a front group disposed on a projection-plane side;
• a rear group disposed on a display-surface side of an image display element inclined with reference to the projection plane;
• and
• an aperture stop disposed on the display-surface side with reference to the front group, wherein
• the front group having a front-group optical axis, the rear group having a rear-group optical axis parallel to the front-group optical axis, the front-group optical axis and the rear-group optical axis being shifted by an amount of shift Δ relative to each other, in a direction perpendicular to the front-group optical axis and the rear-group optical axis,
• the front-group optical axis and the rear-group optical axis being on a shared plane shared by a display-surface normal assumed on the display surface and a projection-plane normal line assumed on the projection plane to intersect with the display-surface normal,
• the rear-group optical axis being tilted on the shared plane at a tilt angle ξ with reference to the display-surface normal,
• when the amount of shift Δ is zero, the tilt angle ξ satisfies a first conditional expression as follows:
• 0<ξ/ξs<1,
• where ξs denotes a tilt angle when Scheimpflug principle is satisfied with reference to the display surface and the projection plane,
• assuming that a straight line connecting a center of the projection plane and a center of the display surface is a reference line, the front-group optical axis is shifted in a direction perpendicular to the rear-group optical axis, by an amount of shift Δ, where Δ≠0, with reference to a tilt-reference state where a common optical axis of the front group and the rear group is tilted around a point of intersection of the reference line and a lens surface of the front group on the projection-plane side by the tilt angle ξ with reference to a non-shifted reference state in which the common optical axis matches the reference line,
• the front-group optical axis and the rear-group optical axis are shifted as a whole in a direction perpendicular to the front-group optical axis while maintaining the tilt angle ξ and the amount of shift Δ,
• the rear-group optical axis is shifted by an amount of shift Δ2 with reference to the front-group optical axis, and
• a second conditional expression as follows is satisfied:
• 0.000047 (/mm)<|Δ2/f2|/f<0.001 (/mm), where
• f2 denotes focal length of the rear group, and
• f denotes focal length of the front group and the rear group.