| 摘要 |
PROBLEM TO BE SOLVED: To provide a compact projection lens which is composed of three groups; negative, positive and positive, is insertable with a color synthesis optical system but has an adequate back focus not longer than needed and telecentric characteristics by satisfying respective prescribed conditions, has good optical performance small in distortion and chromatic aberration and has a simple inner focus structure and a projector. SOLUTION: This projection lens is disposed, successively from a magnification side, with the first lens group G1 having negative refracting power, the second lens group G2 having positive refracting power and the third lens group G3 having positive refracting power. Focus regulation is executed by moving the lens L5 arranged on the extreme reduction side of the first lens group G1 on the optical axis X. The condition equation 0.8<DG12/f<3.0 is satisfied when the spacing between the first lens group G1 and the second lens group G2 is defined as DG12 and the focal length over the entire system as (f). |
