TECHNICAL FIELD

The present disclosure relates to a projection lens system that projects an image of a reduction side into a magnification side, and an image projection device including the projection lens system.

BACKGROUND ART

PTL 1 discloses an optical system for successfully correcting chromatic aberrations and reducing a shift in focus position due to a temperature change in an image projection device and an imaging device. In the optical system of PTL 1, at least two positive lenses in which the Abbe number, anomalous dispersion property, rate of change in refractive index with respect to temperature changes, and the like are set in appropriate ranges are disposed closer to the reduction side than a diaphragm. As a result, the shift in the focus position caused by the change in refractive index due to the temperature change can be reduced, while the axial chromatic aberration is successfully corrected by increasing the width of an axial light flux. PTL 1 describes that a lamp used as a light source is a cause of high temperature in the image projection device.

CITATION LIST

Patent Literature

PTL 1: Unexamined Japanese Patent Publication No. 2011-053663

SUMMARY

The present disclosure provides a projection lens system and an image projection device that can improve the image quality of an image when the brightness of the image projection device is increased.

A projection lens system according to the present disclosure is a lens system that projects an image of a reduction side into a magnification side. The projection lens system includes a diaphragm, a plurality of positive lenses, and a plurality of negative lenses. The plurality of positive lenses include a first positive lens that is closer to the magnification side than the diaphragm is and is closest to the diaphragm, a second positive lens that is second closest to the diaphragm after the first positive lens on the magnification side, and a third positive lens that is closer to the reduction side than the diaphragm is and is closest to the diaphragm. The first to third positive lenses satisfy following conditions (1) to (3). The plurality of negative lenses include a first negative lens that is closer to the magnification side than the diaphragm is and is closest to the diaphragm and a second negative lens that is closer to the reduction side than the diaphragm is and is closest to the diaphragm. The first and second negative lenses satisfy following conditions (4) to (6). At least one positive lens of the first to third positive lenses satisfies following conditions (7) and (8),
Tp1>99%  (1)
Tp2>99%  (2)
Tp3>99%  (3)
Tn1>99%  (4)
Tn2>99%  (5)
αn1<100×10−7[/° C.]  (6)
dn/dt<−4.5×10−6(7)
|fp/fw|>1.3  (8)

where

Tp1 indicates an internal transmittance of light having a wavelength of 460 nm when a lens material of the first positive lens has a thickness of 10 mm,

Tp2 indicates an internal transmittance of light having a wavelength of 460 nm when a lens material of the second positive lens has the thickness mentioned above,

Tp3 indicates an internal transmittance of light having a wavelength of 460 nm when a lens material of the third positive lens has the thickness mentioned above,

Tn1 indicates an internal transmittance of light having a wavelength of 460 nm when a lens material of the first negative lens has the thickness mentioned above,

Tn2 indicates an internal transmittance of light having a wavelength of 460 nm when a lens material of the second negative lens has the thickness mentioned above,

αn1 indicates a linear expansion coefficient of the lens material of the first negative lens at room temperature,

dn/dt indicates a temperature coefficient of a relative refractive index of a lens material of the at least one positive lens at room temperature,

fp indicates a focal length of the at least one positive lens, and

fw indicates a focal length at the wide-angle end of a whole system.

An image projection device according to the present disclosure includes the projection lens system described above and an image forming element. The image forming element forms an image.

According to the projection lens system and the image projection device according to the present disclosure, it is possible to improve the image quality of an image when the brightness of the image projection device is increased.

