Focus fixing lens

Abstract

The invention provides a fixed focus lens, comprising a first lens group, a second lens group and a third lens group which are sequentially arranged from the object side to the image side; the first lens group is provided with negative dioptre and comprises three lenses which are arranged from the object side to the image side; the lens of the first lens group closest to the object side is a non-spherical lens; the second lens group is provided with positive dioptre and comprises two lenses which are arranged from the object side to the image side; the third lens group is provided with positive dioptre and comprises six lenses which are arranged from the object side to the image side; furthermore, the dioptre of the lenses of the third lens group is sequentially negative, positive, negative, positive, positive and positive from the object side to the image side; the fixed focus lens meets the conditions as follows: (i) the absolute value of F1 / F is less than 3 and more than 0.2; (ii) F2 / F is less than 3 and more than 0.5; (iii) F3 / F is less than 3.5 and more than 0.5, wherein, F, F1, F2 and F3 are respectively the effective focus length of the fixed focus lens, the first lens group, the second lens group and the third lens group.

Description

technical field [0001] The present invention relates to a lens, and in particular to a fixed-focus lens. Background technique [0002] Please refer to FIG. 1 , a conventional fixed-focus lens 100 disclosed in US Pat. image side) a first lens group (lens group) 110 , a second lens group 120 and a third lens group 130 arranged in sequence. A light valve 50 is provided on the image side. The first lens group 110 includes four lenses 112 , 114 , 116 , 118 with negative refractive power, wherein the lens 112 is an aspheric lens. The second lens group 120 includes two lenses 122 , 124 , the diopters of the two lenses 122 , 124 are positive and negative respectively, and the two lenses 122 , 124 form a cemented lens 121 . The third lens group 130 includes six lenses 131, 132, 133, 135, 136, 137, and the diopters of the six lenses 131, 132, 133, 135, 136, 137 are positive and negative in sequence from the object side to the image side , positive, positive, positive, positive. I...

AI Technical Summary

Problems solved by technology

However, in the third lens group 130, the last lens 137 is an aspheric lens, and aspheric lenses made of glass are relatively expensive, which will lead to a higher cost of the fixed-focus lens 100

If in order to reduce the cost, the lens 137 is designed as a relatively cheap plastic aspheric lens, the lens 137 is easily deformed because it cannot withstand high temperature, which will make the reliability of the fixed-focus lens 100 poor.

Images