| 摘要 |
PROBLEM TO BE SOLVED: To obtain an image-formation lens whose image-formation performance is hardly changed by the change of temperature or humidity, which is made small in size and light in weight and inexpensive and whose image-formation performance is excellent by constituting a lens system of a 1st group having positive refractive power and a 2nd group having negative refractive power and making a lens having a large aperture a plastic lens. SOLUTION: This image-formation lens is a lens system provided with a 1st group having positive refractive power and a 2nd group having negative refractive power in order from an object side and performing variable power by changing a space between the 1st and the 2nd groups. Then, the 1st group is constituted of a plastic lens having weak refractive power, a glass lens having negative refractive power and a glass lens having positive refractive power in order from the object side, and the 2nd group is constituted of a plastic lens having weak refractive power and a plastic lens having negative refractive power in order from the object side. Thus, the entire length of the lens system, that is, a distance from the surface of the lens system nearest to the object side to an image surface can be made short. Further, the cost is reduced and simultaneously the lens system can be made light in weight.
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