Projection optical system

Abstract

The 1-2nd lens group is divided into three lens groups which move when focusing is performed during the magnification change. Even in a case in which the second optical group is formed of one mirror, it is possible for a primary image to contain appropriate aberration and to hereby reduce aberration of an image which is finally projected onto a screen through the second optical group.

Description

BACKGROUND[0001]1. Technical Field[0002]The present invention relates to a projection optical system suitable for being incorporated in a projector which performs enlargement projection of an image of an image display element.[0003]2. Related Art[0004]A refraction optical system configured to include a plurality of lenses as a projection optical system for a projector which can perform projection from a short distance and can obtain a large picture plane by having a wide angle of view substantially equal to a half angle of view of 60 degrees, is proposed (see JP-A-2007-147970). However, in a case where a significantly wide angle of view is obtained by the refraction optical system configured only of the lenses, there are drawbacks in that, particularly, a lens disposed on the enlargement side is likely to be enormously increased in side. In addition, when the refraction optical system performs projection at a wide angle of view, it is considered that a large number of lenses are nee...

AI Technical Summary

Benefits of technology

The invention provides a projection optical system that can change magnification widely for use in a proximity type projector. It can be used with high-resolution image display elements.

Problems solved by technology

However, in a case where a significantly wide angle of view is obtained by the refraction optical system configured only of the lenses, there are drawbacks in that, particularly, a lens disposed on the enlargement side is likely to be enormously increased in side.

In addition, the F-number is about 3 and it is dark and an optical system using a transmissive liquid crystal is defective in terms of brightness.

Moreover, two mirrors have a aspheric surface, which causes difficulty in terms of achieving accuracy and assembly.

As above, in the refraction / reflection complex optical system, an ultra-wide angle of view is obtained but it is difficult to decrease the entire length, and thereby there are drawbacks in that the mirror is increased in size.

For example, the system is not suitable for equipment such as a front projector in which portability is important.

However, since the system is applied only to the F-number of about 1.8, sufficient brightness is not obtained.

At this time, since the second optical group is configured on of one mirror, it is difficult to individually correct aberration.

Further, in the ultra-wide angle projection optical system having the configuration described above, when the projection magnification is changed, the aberration fluctuation is likely to increase because an angle of view is abnormally wide.

In addition, in the refraction and reflection complex optical system having the ultra-wide angle, since a light flux from the first optical group formed of the refraction optical system is reflected from the mirror of the second optical group and returns to the first optical group, there is a concern that the lens of the first optical group on the second optical group side will interfere with the light flux returning from the second optical group.

The F3 lens group can be, for example, a aspheric lens formed of a resin; however, since the material has a significant shrinkage factor as general characteristics of a resin-molded lens, it is difficult to secure accuracy of size of the surfaces, compared to the glass-molded lens.

In addition, when the power becomes excessively strong, an uneven thickness ratio representing a ratio of the lens thickness in the vicinity of the optical axis and the lens thickness at the outer circumferential portion is increased.

Then, it is possible to have an influence on the performance because internal distortion is likely to occur at a gate portion or at the outer circumferential portion.

Therefore, it is difficult to maintain frame accuracy or assembly accuracy.

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