| 摘要 |
PROBLEM TO BE SOLVED: To provide an image forming optical system constituted so that a light source having comparatively wide wavelength can be used and the throughput of processing can be enhanced by highly correcting chromatic aberration in the ultraviolet-ray area of the image forming optical system. SOLUTION: This image forming optical system is composed of a positive, a negative, a positive, a positive aand a positive lens groups G1-G5 from an object side. Then, a set (a1) consisting of a positive quartz lens and a negative fluorite lens is included in the 1st lens group G1 and sets (b1)-(b8) consisting of a positive fluorite lens and a negative quartz lens are included in the 4th lens group G4. Then, the synthesized refractive power of the mutually adjacent surfaces of the positive quartz lens and the negative fluorite lens constituting the set (a1) and that of the mutually adjacent surfaces of the positive fluorite lens and the negative quartz lens constituting the sets (b1)-(b8) are properly prescribed. |
