Projection lens system

A projection lens system having a plurality of CRTs each for generating a different monochrome image and at least one dichromatic mirror for chromatically mixing the images, so as to enlarge and project a composite color image onto a screen, said system comprising:

• a first lens group for correcting spherical aberration and coma aberration;
• a second lens group for correcting chromatic aberration;
• a third lens group for providing the main optical power for the whole system;
• and
• a fourth lens group for correcting petzval aberration, wherein said first, second and third lens groups are sequentially disposed forward of said dichromatic mirror, said fourth lens group is disposed between said CRTs and dichromatic mirror, and said first, second, third and fourth lens groups are formed with seven lenses in total and satisfy the following conditions
• 0. 95<f/f.sub.6 <1.05
• -0.1<f/(f.sub.3 +f.sub.4 +f.sub.5)<0.1
• v<40
• where f is the focal length of the optical system;
• fi is the focal length of ith lens from the screen, where i is a positive interger, and v is the negative dispersion value of the second lens group.