Zoom lens

Abstract

The invention discloses a pair of variable focus lens, which comprises in turn from the object side: a set of lens (GR1), a second set of lens (GR2), a diaphragm (St), a third set of lens (GR3) and a fourth set of lens (GR4). The first set of lens (GR1) and the third set of lens (GR3) are secured sets, and the second set of lens (GR2) and the fourth set of lens (GR4) are movable sets. A right angle prism (LP) is arranged in the first set of lens (GR1), which also meets the conditions that: wherein, NP indicates a refractive index of the right angle prism (LP) against a Line d, VP represents an abbe number of the right angle prism (LP) against the Line d, D2-6 shows the distance between the side of the image on the first lens and the optical axis of the object side on the second lens within the first set of lens, and fW indicates a focus of the whole system from the wide angle. NP is more than 1.71 and less than 1.80 (1); VP is larger than 30 (2); D2-6 is larger than 1.4 / fW is less than 1.9 (3).

Description

technical field [0001] The present invention relates to a zoom lens suitable for use in small devices having an imaging function, especially digital still cameras, mobile phones with cameras, personal digital assistants, and the like. Background technique [0002] Recently, in imaging devices such as digital still cameras, further miniaturization of the entire device is required as the size of CCD (Charge Coupled Device) and CMOS (Complementary Metal Oxide Semiconductor) advances. Along with this, imaging lenses, especially zoom lenses, are required to be thinner by shortening the overall length or the like. Conventionally, among zoom lenses used in digital still cameras and the like, a zoom lens composed of three groups is advantageous for shortening the overall length, and has been widely used when the zoom ratio is about 3 times (see Patent Document 1). . In the zoom lens with this configuration, each group is movable, and even if a certain length is required when in us...

AI Technical Summary

Problems solved by technology

[0008] However, although the zoom lens described in Patent Document 2 has a large zoom ratio and a bright F value, it has the following problems: the first lens group is large, and the number of lens elements in the whole is also large, so it is not suitable for thinning.

Moreover, the zoom lens described in Patent Document 3 has the following problems: although the number of lens elements is small and the angle of view at the wide-angle end is large, the first lens group is very large, and the refractive power of the right-angle prism is very low. It is difficult to produce total reflection, so a reflective coating is required on the reflective surface of the rectangular prism, which reduces the transmittance of the entire system and increases the cost

In addition, the zoom lens described in Patent Document 4 has various embodiments, and there is a compact example in which the number of lens elements is small, but it uses a material with a high refractive index and high dispersion for the right-angle prism, so there is a so-called reduction in reliability. The issue of transmittance on the short-wavelength side of visual light

That is, in Patent Document 4, as an example, a rectangular prism of a material having a refractive index higher than 1.8 with respect to the d-line and an Abbe number smaller than 30 is used. However, such a high refractive index, high dispersion, and sufficiently high transmittance The material does not actually exist and is not practical

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