A rear focusing objective lens

Abstract

The present invention provides a rear-mounted focusing objective lens, which is arranged between a front lens and a camera, with an optical axis as a rotation center, and includes a first lens, a cemented sheet, a liquid lens, an aperture, a second lens, a third lens, and a fourth lens in order from the object side to the image side. The present invention adopts an image-side telecentric optical design, and realizes automatic focusing by adjusting the surface curvature of the liquid lens. No mechanical displacement occurs during the entire focusing process, and rapid focusing can be completed once within 10ms. The focusing efficiency is high, the cost is low, and the camera and lens with a standard defined interface can be used, which greatly expands the scope of application.

Description

Technical Field

[0001] The invention relates to a design technology of an optical system, in particular to a rear-positioned focusing objective lens. Background Art

[0002] In the field of optical imaging, how to quickly achieve autofocus is a problem that all imaging systems will face. The current mainstream practices in the market are: 1. Use a motor inside the lens to drive the lens group to make linear motion along the optical axis to change the distance between the lens group and the chip. This is an optical lens with autofocus. 2. Install a VCM motor on the camera chip end, keep the lens still, and achieve autofocus by changing the distance between the chip and the lens. This is a camera with autofocus. 3. Install a linear electric platform on the fixed end of the camera and lens, and change the focus position through overall movement. This is a focusing method with an external platform. These three focusing methods are actually mechanical motion focusing. Each method requires the optical device on the imaging optical axis to make linear motion along the optical axis. Most of them require the use of algorithms to determine whether the focusing work is completed. Therefore, a focusing movement often needs to be repeated many times to complete, which is not efficient. Moreover, because there are relatively few optical hardware options, sometimes customized development is required, and the combination cost of the motion mechanism and the optical module is relatively high. Therefore, in many scenarios, autofocus is split into multiple focuses to achieve, which greatly wastes hardware costs and reduces work efficiency. Summary of the invention

[0003] In view of the above problems, the present invention provides a rear-mounted focusing objective lens, which adopts an image-side telecentric optical design, designs parameters such as the curvature of all lenses in the focusing objective lens, the optical spacing between lenses, and the material of each lens, and realizes automatic focusing by adjusting the surface curvature of the liquid lens. No mechanical displacement occurs during the entire focusing process, and rapid focusing can be completed once within 10ms. The focusing efficiency is high and the cost is low. It can be used with cameras and lenses with standard defined interfaces, greatly expanding the scope of application.

[0004] In order to achieve the above object, the rear-focus objective lens provided by the present invention has the following technical solutions:

[0005] The focusing objective lens is arranged between the front lens and the camera, with the optical axis as the rotation center, and includes a first lens, a cemented sheet, a liquid lens, an aperture, a second lens, a third lens and a fourth lens in sequence from the object side to the image side.

[0006] Specifically, the total optical length from the center of curvature of the object surface of the first lens to the image surface is 118 mm.

[0007] Specifically, the optical distance from the first lens to the adhesive sheet is 11.6 mm, and the optical distance from the adhesive sheet to the liquid lens is 1 mm.

[0008] Specifically, the optical distance from the liquid lens to the aperture is 1 mm, and the optical distance from the aperture to the second lens is 2 mm.

[0009] Specifically, the optical interval from the second lens to the third lens is 13.6 mm, and the optical interval from the third lens to the fourth lens is 5.77 mm.

[0010] Specifically, the optical distance from the fourth lens to the image plane is 16 mm.

[0011] Specifically, the optical magnification of the focusing objective lens is 1X, and the object surface diameter of the focusing objective lens is 11 mm.

[0012] Specifically, the object surface of the first lens is a convex spherical surface with a curvature radius of 76.49 mm, and the image surface is a concave spherical surface with a curvature radius of -76.49 mm; the cemented sheet includes a first cemented lens and a second cemented lens, the object surface of the first cemented lens is a concave spherical surface with a curvature radius of -18.85 mm, and the image surface is a concave spherical surface with a curvature radius of -6.13 mm, the object surface of the second cemented lens is a concave spherical surface with a curvature radius of -6.13 mm, and the image surface is a concave spherical surface , the radius of curvature is -11.3mm; the object surface of the second lens is a convex spherical surface with a radius of curvature of 15.3mm, and the image surface is a concave spherical surface with a radius of curvature of -90.6mm; the object surface of the third lens is a concave spherical surface with a radius of curvature of -10.785mm, and the image surface is a convex spherical surface with a radius of curvature of 10.787mm; the object surface of the fourth lens is a concave spherical surface with a radius of curvature of -21.82mm, and the image surface is a convex spherical surface with a radius of curvature of 21.82mm.

[0013] Specifically, the first lens is made of crown glass (H-K9L); the first cemented lens is made of crown glass (H-K9L), the second cemented lens is made of heavy flint glass (H-ZF4); the second lens is made of heavy lanthanum flint glass (H-ZLAF75A); the third lens is made of heavy lanthanum flint glass (H-ZLAF75A); and the fourth lens is made of heavy flint glass (H-ZK3).

[0014] Specifically, the rear focusing objective lens further includes a driving circuit, and the driving circuit is used to adjust the surface curvature of the liquid lens.

[0015] The rear focusing objective lens provided by the present invention realizes automatic focusing through optical design and the characteristics of the liquid lens without changing the optical parameters of the front lens. No mechanical displacement occurs during the entire focusing process, and rapid focusing can be completed once within 10 ms. The focusing efficiency is high and the cost is low. The lens can be used in conjunction with cameras and lenses with standard defined interfaces, greatly expanding the scope of application. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for use in the embodiments of the present invention are briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can also be obtained based on these drawings.

[0017] Figure 1 A schematic diagram of the optical path structure of the rear-focus objective lens provided by the present invention;

[0018] Figure 2 for Figure 1 System ray fan diagram of the focusing objective;

[0019] Figure 3 for Figure 1 System field curvature and distortion diagrams of focusing objectives;

[0020] Figure 4 for Figure 1 System MTF curve of the focusing objective lens;

[0021] Figure 5 for Figure 1 System image plane illumination diagram of the focusing objective.

[0022] Legend:

[0023] 1 is the first lens; 2 is the cemented sheet; 3 is the liquid lens; 4 is the aperture; 5 is the second lens; 6 is the third lens; 7 is the fourth lens. DETAILED DESCRIPTION

[0024] The technical solution of the present invention will be described clearly and completely below in conjunction with the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the described embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0025] The present invention provides a rear focus lens, which is arranged between the front lens and the camera. Figure 1 As shown, with the optical axis as the rotation center, the focusing objective lens includes, from left to right, a first lens 1, a cemented sheet 2, a liquid lens 3, an aperture 4, a second lens 5, a third lens 6 and a fourth lens 7.

[0026] In the design process of the focusing objective lens, the image plane of the front lens that forms the front image is used as the object plane of the focusing objective lens, and the image formed by the focusing objective lens is an overall image. The image-side telecentric optical design is adopted, and the focusing objective lens is designed according to the object plane diameter of 11mm.

[0027] The total optical length of the entire rear-focusing objective lens system, that is, the total optical length from the center of curvature of the object surface of the first lens 1 to the image plane is set to 118 mm, wherein the optical spacing from the first lens 1 to the adhesive sheet 2 is 11.6 mm, with a tolerance of ±0.03 mm; the optical spacing from the adhesive sheet 2 to the liquid lens 3 is 1 mm, with a tolerance of ±0.02 mm; the optical spacing from the liquid lens 3 to the diaphragm 4 is 1 mm, with a tolerance of ±0.01 mm; the optical spacing from the diaphragm 4 to the second lens 5 is 2 mm, with a tolerance of ±0.03 mm; the optical spacing from the second lens 5 to the third lens 6 is 13.6 mm, with a tolerance of ±0.05 mm; the optical spacing from the third lens 6 to the fourth lens 7 is 5.77 mm, with a tolerance of ±0.02 mm; and the optical spacing from the fourth lens 7 to the focusing object image plane is 16 mm, with a tolerance of ±0.1 mm.

[0028] All lenses in the focusing objective are made of Chengdu Guangming colorless glass, and the first lens 1 is made of crown glass (H-K9L); the cemented sheet 2 includes a first cemented lens and a second cemented lens, the first cemented lens is made of crown glass (H-K9L), and the second cemented lens is made of heavy flint glass (H-ZF4); the second lens 5 is made of heavy lanthanum flint glass (H-ZLAF75A); the third lens 6 is made of heavy lanthanum flint glass (H-ZLAF75A); and the fourth lens 7 is made of heavy flint glass (H-ZK3).

[0029] When describing the curvature of the lens in the focusing objective, the left curvature of each lens is defined as the object surface curvature of the lens, the right curvature is defined as the image surface curvature, and the curvature of the convex surface toward the object surface is positive, and the curvature of the convex surface toward the image surface is negative. The curvature data of each lens in the focusing objective are as follows: the object surface of the first lens 1 is a convex spherical surface with a curvature radius of 76.49mm, and the image surface is a concave spherical surface with a curvature radius of -76.49mm; the object surface of the first cemented lens is a concave spherical surface with a curvature radius of -18.85mm, and the image surface is a concave spherical surface with a curvature radius of -6.13mm; the object surface of the second cemented lens is a concave spherical surface with a curvature radius of -6.13mm, and the image surface is a concave spherical surface with a curvature radius of -11.3mm; the object surface of the second lens 5 is a convex spherical surface with a curvature radius of 15.3mm, and the image surface is a concave spherical surface with a curvature radius of -90.6mm; the object surface of the third lens 6 is a concave spherical surface with a curvature radius of -10.785mm, and the image surface is a convex spherical surface with a curvature radius of 10.787mm; the object surface of the fourth lens 7 is a concave spherical surface with a curvature radius of -21.82mm, and the image surface is a convex spherical surface with a curvature radius of 21.82mm. The surface tolerance of all curvatures is aperture 3-4, and the local aperture is 0.3-0.5.

[0030] The focusing lens is also provided with a driving circuit, which changes the surface curvature of the liquid lens 3 by changing the driving voltage, and finally changes the position of the overall focusing image plane of the focusing lens. No mechanical displacement occurs during the entire focusing process, and rapid focusing can be completed in one go within 10 milliseconds.

[0031] Since the focus position of the entire lens group (including the front lens and the focusing lens) can be changed by adjusting the curvature of the liquid lens 3, the image plane position and the object plane position of the focusing lens have an adjustable range, and the size of the adjustable range depends on the optical parameters of the front lens.

[0032] Figure 2 Shown is a systematic ray fan diagram of a focusing objective, showing the set of aberrations produced in different fields of view, with differences in meridional and sagittal aberrations visible for each field of view. Figure 3 Shown is the system field curvature and distortion diagram of the focusing objective lens, which shows the field curvature and distortion of the focusing objective lens system. The left side is the field curvature (image plane curvature). It can be seen that the maximum deviation of the image plane curvature will not exceed 0.2mm and can be ignored. The right figure shows the optical distortion. The maximum distortion is less than 0.2%, which meets the design requirements. Figure 4 Shown is a system MTF curve of the focusing objective lens, with the horizontal axis being line pairs / mm and the vertical axis being frequency. The solid and dotted lines represent the meridian and sagittal directions. Figure 5 The figure shows the system image plane illumination diagram of the focusing objective lens. It can be seen that the illumination at the center and edge of the imaging plane is such that the image illumination at the edge can reach more than 95% of the center illumination.

[0033] The system working environment of the focusing objective lens provided by the present invention is a visible light environment, and the working band is between 485nm-655nm.

[0034] When the rear-positioned focusing objective lens with a liquid lens provided by the present invention is used for automatic focusing, the following steps are included:

[0035] Step S1: installing the focusing lens between the front lens and the camera through a threaded connection;

[0036] Step S2: adjusting the surface curvature of the liquid lens to achieve automatic focusing of the entire optical system.

[0037] The rear focusing lens with a liquid lens provided by the present invention is suitable for industrial cameras with a C-mount design of less than 2 / 3 inches. The optical magnification of the focusing lens is 1 times. Therefore, for the industrial camera equipped with the focusing lens, the optical magnification of the entire system is determined by the front lens.

[0038] It can be understood that the above specific description of the present invention is only used to illustrate the present invention and is not limited to the technical solutions described in the embodiments of the present invention. Those skilled in the art should understand that the present invention can still be modified or replaced by equivalents to achieve the same technical effects; as long as the use requirements are met, they are within the protection scope of the present invention.

Claims

1. A rear focus lens, arranged between the front lens and the camera, characterized in that: With the optical axis as the rotation center, the focusing objective lens is composed of a first lens, a cemented sheet, a liquid lens, an aperture, a second lens, a third lens and a fourth lens in sequence from the object side to the image side; The object surface of the first lens is a convex spherical surface with a curvature radius of 76.49 mm, and the image surface is a concave spherical surface with a curvature radius of -76.49 mm; The cemented sheet includes a first cemented lens and a second cemented lens, wherein the object surface of the first cemented lens is a concave spherical surface with a curvature radius of -18.85 mm, and the image surface is a concave spherical surface with a curvature radius of -6.13 mm, and the object surface of the second cemented lens is a concave spherical surface with a curvature radius of -6.13 mm, and the image surface is a concave spherical surface with a curvature radius of -11.3 mm; The object surface of the second lens is a convex spherical surface with a curvature radius of 15.3 mm, and the image surface is a concave spherical surface with a curvature radius of -90.6 mm; The object surface of the third lens is a concave spherical surface with a curvature radius of -10.785 mm, and the image surface is a convex spherical surface with a curvature radius of 10.787 mm; The object surface of the fourth lens is a concave spherical surface with a curvature radius of -21.82 mm, and the image surface is a convex spherical surface with a curvature radius of 21.82 mm.

2. The rear-focus objective lens according to claim 1, characterized in that: The total optical length from the object surface curvature center of the first lens to the image surface is 118 mm.

3. The rear-focus objective lens according to claim 2, characterized in that: The optical distance from the first lens to the adhesive sheet is 11.6 mm, and the optical distance from the adhesive sheet to the liquid lens is 1 mm.

4. The rear-focus objective lens according to claim 3, characterized in that: The optical distance from the liquid lens to the aperture is 1 mm, and the optical distance from the aperture to the second lens is 2 mm.

5. The rear-focus objective lens according to claim 4, characterized in that: The optical interval from the second lens to the third lens is 13.6 mm, and the optical interval from the third lens to the fourth lens is 5.77 mm.

6. The rear-focus objective lens according to claim 5, characterized in that: The optical distance from the fourth lens to the image plane is 16 mm.

7. The rear-focus objective lens according to claim 1, characterized in that: The optical magnification of the focusing objective lens is 1X, and the object surface diameter of the focusing objective lens is 11 mm.

8. The rear-focus objective lens according to claim 1, characterized in that: The first lens is made of crown glass; the first cemented lens is made of crown glass, the second cemented lens is made of heavy flint glass; the second lens is made of heavy lanthanum flint glass; the third lens is made of heavy lanthanum flint glass; and the fourth lens is made of heavy flint glass.

9. The rear-focus objective lens according to claim 1, characterized in that: The invention also comprises a driving circuit, wherein the driving circuit is used to adjust the surface curvature of the liquid lens.

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