| 摘要 |
An image forming lens system including a positive front lens group, a diaphragm, and a rear lens group, in this order from an object to be imaged. The front lens group is made of optical glass. The rear lens group is made of a single meniscus plastic lens having opposed aspherical lens surfaces with a concave surface adjacent to the diaphragm. The lens system satisfies the following relationships: f0x|1/fR-1+1/fR-2|<0.3 -4<f0/rR-1<-0.7 DELTA XR-1/f0<0 DELTA XR-2/f0<0 0.1<dR/f0. In the above, fR-1 (=rR-1/n-1) represents the focal length of the first surface of the plastic lens, fR-2(=rR-2/1-n) represents the focal length of the second surface of the plastic lens, f0 represents the focal length of the whole lens system, n represents the refractive index of the plastic lens at a reference wavelength, rR-1 represents the radius of curvature of the first surface of the plastic lens, rR-2 represents the radius of curvature of the second surface of the plastic lens, DELTA XR-1 represents the amount of aspheric deviation of the first surface of the plastic lens at an effective radius thereof, DELTA XR-2 represents the amount of aspheric deviation of the second surface of the plastic lens at an effective radius thereof, and dR represents the thickness of the plastic lens.
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