| 摘要 |
A fixed focus lens includes, numbered in order of location from an object side to an image side, a first lens, a second lens, a third lens, and a fourth lens. The first lens is a biconvex lens with a positive refractive power, and the second lens is a convex-concave lens with a negative refractive power. The third lens is a concave-convex lens with a positive refractive power, and the fourth lens is an aspherical lens having a negative refractive power in the centre portion thereof and a positive refractive power at the periphery portion thereof. The fixed focus lens satisfies the condition: 1.0>|(1/r2−1/r1)|>0.6, where r1 denotes the radius of curvature of a front surface of the second lens and r2 denotes the radius of curvature of a rear surface of the first lens.
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