CN108646393B

CN108646393B - Long focus lens

Info

Publication number: CN108646393B
Application number: CN201810772095.7A
Authority: CN
Inventors: 吴冬芹; 尚洁阳; 盛亚茗
Original assignee: Jiaxing Zhongrun Optical Technology Co Ltd
Current assignee: Jiaxing Zhongrun Optical Technology Co Ltd
Priority date: 2018-07-13
Filing date: 2018-07-13
Publication date: 2024-03-29
Anticipated expiration: 2038-07-13
Also published as: CN108646393A

Abstract

A tele lens sequentially includes, in an optical axis direction from an object side to an image side: a first lens group, a diaphragm, and a second lens group, wherein: the second lens group comprises at least one aspheric lens or two cemented lenses. The optical device solves the problem that field curvature and coma influence a long-focus optical system, remarkably improves the image quality of the whole picture, and has small depth of field and larger magnification.

Description

Long focus lens

Technical Field

The invention relates to a technology in the field of optical devices, in particular to a tele lens.

Background

At present, for a long-distance small-target long-focus high-definition lens, civil single counter and replacing the quasi-tele lens. The lens is large in design target surface, resolution ratio can be greatly reduced on a small target surface imaging device, and the structure is complex and the price is high, so that a special small target surface, a long-focus lens with simple structure, low price and high imaging quality is required to be designed, and the lens is specially used for capturing details of remote objects. For a long-focus lens, field curvature and coma are main phase differences affecting the phase quality, the larger the field curvature and the coma are, the more the image quality of an edge view field is reduced, so that the uniform and consistent good imaging quality of the whole view field is difficult to ensure, meanwhile, if the illuminance of the whole image surface is uneven, the center is brighter than the periphery, dark corners can appear on the imaging edge, and the whole definition of a picture is affected.

Disclosure of Invention

Aiming at the problems of the existing long-focus optical system, the invention provides a long-focus lens, solves the influence of field curvature and coma on the long-focus optical system and remarkably improves the image quality of the whole picture, and the optical equipment has small depth of field and larger magnification.

The invention is realized by the following technical scheme:

the invention sequentially comprises the following steps from an object side to an image side along the optical axis direction: a first lens group, a diaphragm, and a second lens group, wherein: the second lens group comprises at least one aspheric lens or two cemented lenses.

The first lens group includes: at least three lenses with positive focal power and two lenses with negative focal power, specifically: a first lens having positive optical power, a second lens having positive optical power, a third lens having negative optical power, a fourth lens having positive optical power, and a fifth lens having negative optical power, wherein: the third lens and the fourth lens form a cemented lens.

Preferably, the refractive index of the third lens satisfies 1.62< nd <1.64, and the abbe number satisfies 63.79< vd <65.38; the refractive index of the rear lens satisfies 1.465< Nd <1.5, and the Abbe number satisfies 76.75< Vd <81.61.

Preferably, the combined focal length of the cemented lens satisfies-1.42 < f34/EFL < -0.84, thereby reducing tolerance sensitivity of the lens.

Preferably, the first lens satisfies: 4.85< sag1/CTG1<5.20, wherein: SAG1 is the sagittal height of the object side surface of the first lens, CTG1 is the center thickness of the first lens, the incidence angle of the chief ray on the imaging plane can be reduced by meeting the requirement of the above formula, and the chip matching degree is higher.

Preferably, the focal lengths of the first lens and the second lens satisfy: 0.29< f1/EFL <0.32,0.30< f2/EFL <0.33, wherein: f1 is the effective focal length of the first lens, and f2 is the effective focal length of the second lens, so that the requirements of the relational expression are met, and miniaturization of the lens is guaranteed while long-focus characteristics are considered.

The second lens group is realized by adopting any one of the following structures:

(1) two pieces of the adhesive lenses are adhered together,

(2) an aspherical lens and a cemented lens,

(3) one aspherical lens and two lenses.

The aspherical lens is preferably a plastic aspherical lens, the refractive index of the aspherical lens meets Nd=1.63, the Abbe number of the aspherical lens meets Vd=23.62, and chromatic aberration and coma aberration of the tele lens can be reduced by utilizing the plastic aspherical lens.

The seventh lens of the two lenses satisfies the following conditions: f7/efl= -0.12.

The eighth lens satisfies the following conditions: f8/efl=0.08, refractive index nd= 1.9459, abbe number satisfying vd=17.98, and chromatic aberration and curvature of field are effectively improved in the case of adding one high refractive index low dispersion spherical lens.

The diaphragm is an aperture diaphragm.

The image side is provided with an image acquisition element, and protective glass is arranged in front of the image acquisition element.

The long-focus lens meets the following conditions: 1.97< EFL/TTL <2.02, wherein: EFL is the effective focal length of the telephoto lens, and TTL is the on-axis distance from the object side surface to the image plane of the first lens.

Technical effects

Compared with the prior art, the invention adopts the telephoto optical mechanism, the total length of the optical lens is smaller than the focal length, the structure is compact, the optical lens has small depth of field and larger magnification, and the reasonable optical structure and lens materials are matched, so that the phase difference correction is good, the whole view field has consistent imaging quality, and the tolerance sensitivity is low, thus being suitable for mass production.

Drawings

Fig. 1 is a schematic structural diagram of a tele lens in embodiment 1;

FIG. 2 is a graph of on-axis chromatic aberration and a schematic distortion of the tele lens of example 1;

FIG. 3 is a schematic diagram of the relative illuminance of a telephoto lens in embodiment 1;

fig. 4 is a schematic structural diagram of a tele lens in embodiment 2;

FIG. 5 is a graph of on-axis chromatic aberration and a schematic distortion of a tele lens of example 2;

FIG. 6 is a schematic diagram of the relative illuminance of a telephoto lens in embodiment 2;

fig. 7 is a schematic structural diagram of a tele lens in embodiment 3;

FIG. 8 is a graph of on-axis chromatic aberration and distortion for the tele lens of example 3;

fig. 9 is a schematic diagram of the relative illuminance of the tele lens in embodiment 3;

in the figure: the first to seventh lenses L1 to L7, the first to eighteenth surfaces S1 to S18, the stop S, the cover glass CG, and the imaging plane IMG.

Detailed Description

Example 1

As shown in fig. 1 to 3, the present embodiment discloses a 70mm tele lens, which sequentially includes, from an object side to an image side along an optical axis direction: the lens comprises a first lens group, a diaphragm S, a second lens group, a protective glass CG and an image plane IMG.

The first lens group: the first lens L1 is a lunar convex spherical lens and comprises a first spherical surface s1 (convex surface) and a second spherical surface s2 (concave surface); the second lens L2 is a biconvex spherical lens, including a third spherical surface s3 (convex surface) and a fourth spherical surface s4 (convex surface); the third lens L3 is a lunar convex spherical lens and comprises a fifth spherical surface s5 (convex surface) and a sixth spherical surface s6 (concave surface); the fourth lens L4 is a biconvex spherical lens, and includes a sixth spherical surface s6 (convex surface) and a seventh spherical surface s7 (concave surface); the fifth lens L5 is a biconcave spherical lens, and includes an eighth spherical surface s8 (concave surface) and a ninth spherical surface s9 (concave surface), wherein the third lens L3 and the fourth lens L4 are combined into a first cemented lens.

The second lens group comprises two cemented lenses, wherein: the second cemented lenses L61, L62 are lunar concave spherical lenses including an eleventh spherical surface s11 (concave surface) and a thirteenth spherical surface (concave surface); the third cemented lenses L71, L72 are lunar convex spherical lenses comprising a fourteenth spherical surface s14 (concave surface) and a sixteenth spherical surface (convex surface)

The diaphragm is positioned at the object space and between the first lens group and the second lens group

The specific parameters of the lens of this embodiment are shown in the following table

TABLE 1

The effective focal length of the lens of this embodiment is efl=80 mm, the relative aperture f=8, and the total length TTL of the entire optical system is 40mm, and the structure is as shown in fig. 1.

This embodiment satisfies EFL/ttl=2.0, where: EFL is the effective focal length of the telephoto lens, and TTL is the on-axis distance from the object side surface to the image plane of the first lens.

The third lens L3 is a glass lens, the refractive index of which satisfies nd=1.62, and the abbe number satisfies vd= 63.88; the fourth lens L4 is a glass lens having a refractive index satisfying nd=1.50, an abbe number satisfying vd=76.75, and a combined focal length satisfying f34/efl= -1.05.

As shown in fig. 2, an on-axis chromatic aberration diagram and a distortion diagram of the tele lens according to the present embodiment are shown. The on-axis chromatic aberration diagram shows the degree of deviation of different wavebands from ideal phase plane positions at different light-passing apertures, the horizontal axis shows the offset, and the vertical axis shows the normalized pupil aperture. In the figure, the horizontal axis distance between the wavelengths 587nm and 852nm in the 0.75 pupil is 0.05mm. The distortion chart represents the difference between the actual image height and the ideal image height. The horizontal axis represents the percent distortion and the vertical axis represents the half image height. It can be seen from the figure that the distortion of the present embodiment is within 1.0%, and in general, distortion of the photographed object is indistinguishable to the human eye.

As shown in fig. 3, the full-field relative illuminance curve of the telephoto lens of the present embodiment. As can be seen from the figure, the relative illumination is more than 90% in the full view field range, and the phase surface illumination is uniform without the possibility of dark corners.

Example 2

As shown in fig. 4 to 6, in the present embodiment, compared with embodiment 1, the third lens L3 is a biconcave spherical lens, and includes a fifth spherical surface s5 (concave surface) and a sixth spherical surface s6 (concave surface).

The second lens group in the present embodiment includes: a sixth lens L6, a cemented lens L71, L72, wherein: the sixth lens is a biconcave aspheric lens and comprises an eleventh aspheric surface s11 (concave surface) and a twelfth aspheric surface s12 (concave surface); the cemented lens L7 is a lunar convex spherical lens including a fourteenth spherical surface s14 (concave surface) and a sixteenth spherical surface (convex surface) s16.

Table 2:

in the present embodiment, the sixth lens L6 employs a plastic aspherical surface in which: the aspherical lens coefficients satisfy:

	K	a (4-order coefficient)	B (6 th order coefficient)	C (8-order coefficient)	D (tenth order coefficient)
						s11	63.93741	-0.00384281	0.000341568	1.36215E-05	-1.95425E-06
s12	-57.173	-0.001498529	-8.54273E-05	6.6344E-05	-9.14827E-06

The curvature corresponding to the aspherical radius of the eleventh surface s11 and s12 of the sixth lens L6 is c, the distance from a point on the lens surface to the optical axis is r, the quadric constant of the lens surface is K, and the fourth-order, sixth-order, eighth-order and tenth-order aspherical coefficients of the tenth surface and the second surface are A, B, C, D, respectively. By adopting the plastic aspheric lens, the number of lenses is reduced, and the aspheric lens can well correct chromatic aberration on an axis, so that the phase difference balance between infrared light and blue light is ensured.

The effective focal length of the lens of this embodiment is efl=80 mm, the relative aperture f=7.8, and the total length TTL of the entire optical system is 39.5mm.

This embodiment satisfies EFL/ttl=2.02, where: EFL is the effective focal length of the telephoto lens, and TTL is the on-axis distance from the object side surface to the image plane of the first lens.

The third lens L3 of the present embodiment is a glass lens, the refractive index of which satisfies nd=1.64, and the abbe number satisfies vd= 65.38; the fourth lens L4 is a glass lens having a refractive index satisfying nd= 1.4651, an abbe number satisfying vd= 79.82, and a combined focal length satisfying f34/efl= -0.84.

As shown in fig. 5, an on-axis chromatic aberration diagram and a distortion diagram of the tele lens according to the present embodiment are shown. The on-axis chromatic aberration diagram shows the degree of deviation of different wavebands from ideal phase plane positions at different light-passing apertures, the horizontal axis shows the offset, and the vertical axis shows the normalized pupil aperture. In the figure, the lateral axis distance at wavelengths of 587nm and 852nm in the 0.75 pupil is less than 0.05mm. The distortion chart represents the difference between the actual image height and the ideal image height. The horizontal axis represents the percent distortion and the vertical axis represents the half image height. It can be seen from the figure that the distortion of the present embodiment is within 1.0%, and in general, distortion of the photographed object is indistinguishable to the human eye.

Fig. 6 is a graph showing the relative illuminance of the whole field of view of the telephoto lens of the present embodiment. The graph shows that the relative illumination is more than 90% in the full view field range, the phase surface illumination is uniform, and no dark angle is possible.

Example 3

As shown in fig. 7 to 9, the second lens of the present embodiment is a biconvex spherical lens, including a third spherical surface s3 (convex surface) and a fourth spherical surface s4 (concave surface), compared with embodiment 2; the fifth lens is a biconcave spherical lens, and comprises an eighth spherical surface s8 (concave surface) and a ninth spherical surface s9 (concave surface).

The second lens group in the present embodiment includes: a sixth lens L6, a seventh lens L7, and an eighth lens L8, wherein: the sixth lens is a biconcave aspheric lens and comprises an eleventh aspheric surface s11 (concave surface) and a twelfth aspheric surface s12 (concave surface); the seventh lens L7 is a biconcave spherical lens, including a fourteenth spherical surface s13 (concave surface) and a fourteenth spherical surface s14 (concave surface); the eighth lens L8 is a biconvex spherical lens, and includes a fourteenth spherical surface s15 (convex surface) and a fourteenth spherical surface s16 (convex surface).

The eighth lens L8 can obviously improve on-axis chromatic aberration and reduce distortion under the condition of a high-refractive-index and low-dispersion spherical lens.

TABLE 3 Table 3

	K	a (4-order coefficient)	B (6 th order coefficient)	C (8-order coefficient)	D (10-order coefficient)
						s11	51.332383	-0.006445029	0.000922435	-4.0428E-05	6.60023E-06
s12	-24.29006	-0.001519887	-0.000118653	0.000112657	-1.36619E-05

The curvature corresponding to the aspherical radius of the eleventh surface s11 and s12 of the sixth lens L6 is c, the distance from a point on the lens surface to the optical axis is r, the quadric constant of the lens surface is K, and the fourth-order, sixth-order, eighth-order and tenth-order aspherical coefficients of the tenth surface and the second surface are A, B, C, D, respectively.

The effective focal length of the lens of this embodiment is efl=80 mm, the relative aperture f=8.1, and the total length TTL of the entire optical system is 40.6mm, and the structure is shown in fig. 7.

This embodiment satisfies EFL/ttl=1.97, where: EFL is the effective focal length of the telephoto lens, and TTL is the on-axis distance from the object side surface to the image plane of the first lens.

In this embodiment, the third lens L3 is a glass lens, the refractive index of which satisfies nd=1.619, and the abbe number satisfies vd= 63.79; the fourth lens L4 is a glass lens having a refractive index satisfying nd=1.497, an abbe number satisfying vd=81.61, and a combined focal length satisfying f34/efl= -1.4.

As shown in fig. 8, an on-axis chromatic aberration diagram and a distortion diagram of the tele lens according to the present embodiment are shown. The on-axis chromatic aberration diagram shows the degree of deviation of different wavebands from ideal phase plane positions at different light-passing apertures, the horizontal axis shows the offset, and the vertical axis shows the normalized pupil aperture. In the figure, the horizontal axis distance between the wavelengths 587nm and 852nm in the 0.75 pupil is almost similar, and no chromatic aberration exists. The distortion chart represents the difference between the actual image height and the ideal image height. The horizontal axis represents the percent distortion and the vertical axis represents the half image height. It can be seen from the figure that the distortion of this example is within 0.5% and almost no distortion occurs.

As shown in fig. 9, a graph of the total field of view relative illuminance of the telephoto lens of the present embodiment is shown. The graph shows that the relative illumination is more than 90% in the full view field range, the phase surface illumination is uniform, and no dark angle is possible.

The invention adopts a reasonable optical mechanism, the total length of the optical lens is smaller than the focal length, the structure is compact, the depth of field is small, the magnification is large, and the imaging lens is suitable for shooting distant sceneries and is miniaturized. The reasonable matching of the optical structure and the lens material ensures that the phase difference correction is good, the whole view field has consistent imaging quality, and the tolerance sensitivity is low, thus being suitable for mass production.

The foregoing embodiments may be partially modified in numerous ways by those skilled in the art without departing from the principles and spirit of the invention, the scope of which is defined in the claims and not by the foregoing embodiments, and all such implementations are within the scope of the invention.

Claims

1. The utility model provides a long burnt camera lens, its characterized in that is along the optical axis direction from the object side to the image side by first lens group, diaphragm and second lens group constitute, wherein: the second lens group comprises at least one aspheric lens;

the second lens group consists of a sixth lens, a seventh lens and an eighth lens; wherein: the sixth lens is a biconcave aspheric lens, the seventh lens is a biconcave spherical lens, and the eighth lens is a biconvex spherical lens;

the first lens group consists of three lenses with positive focal power and two lenses with negative focal power, and specifically comprises the following components: a first lens having positive optical power, a second lens having positive optical power, a third lens having negative optical power, a fourth lens having positive optical power, and a fifth lens having negative optical power, wherein: the third lens and the fourth lens form a cemented lens;

the combined focal length of the glued lens in the first lens group meets-1.42 < f34/EFL < -0.84, so that tolerance sensitivity of the lens is reduced; f34 is the combined focal length of the third lens and the fourth lens forming a cemented lens;

the first lens satisfies the following conditions: 4.85< sag1/CTG1<5.20, wherein: SAG1 is the sagittal height of the object side of the first lens, CTG1 is the center thickness of the first lens;

the focal lengths of the first lens and the second lens meet the following conditions: 0.29< f1/EFL <0.32,0.30< f2/EFL <0.33, wherein: f1 is the effective focal length of the first lens, f2 is the effective focal length of the second lens, and meeting the requirements of the relational expression is beneficial to ensuring miniaturization of the lens while considering the long focal length characteristic, wherein: EFL is the effective focal length of a tele lens.

2. The tele lens of claim 1, wherein the refractive index of the third lens satisfies Nd <1.64 of 1.619 or less and the abbe number satisfies Vd <65.38 of 63.79 or less; the refractive index of the fourth lens is 1.465< Nd <1.5, and the Abbe number is 76.75< Vd <81.61.

3. The tele lens of claim 1, wherein the seventh lens and eighth lens each satisfy: f7/efl= -0.12, f8/EFL = 0.08, wherein: f7 is the focal length of the seventh lens, and f8 is the focal length of the eighth lens.

4. The tele lens of claim 1, wherein the tele lens satisfies: 1.97.ltoreq.EFL/TTL.ltoreq.2.02, wherein: TTL is the on-axis distance from the object side surface to the image plane of the first lens.