Wide temperature range wide working spectrum visible light athermalization optical system

Abstract

The present application relates to optical systems, in particular to a wide temperature range wide working spectrum visible light athermalization optical system, used to solve the problem of the prior art in the distance defocus compensation design of close-range imaging. The wide temperature range wide working spectrum visible light athermalization optical system compensates the thermal defocus problem of the optical system at high and low temperatures by matching the refractive index coefficient, dispersion coefficient and thermal expansion coefficient of HZF88GT, HZF7LAGT, HFK95N and HZK9B, ensures high imaging quality in the working temperature range of-40 DEG C to +60 DEG C, does not need to use internal focusing means or external focusing means for thermal defocus compensation, uses the thermal characteristic matching of lens material and barrel structure material to compensate the imaging blur caused by temperature change, and has high reliability.

Description

TECHNICAL FIELD

[0001] The present application relates to an optical system, in particular to a visible light athermalization optical system with wide temperature range and wide working spectrum. BACKGROUND

[0002] Optical measurement equipment, as an effective measurement means, is widely used in various scientific research and industrial measurement due to its high measurement accuracy, strong real-time performance, and simple and convenient operation. However, under field test conditions, the change of environmental temperature has a significant impact on the performance of optical measurement equipment.

[0003] Firstly, the change of environmental temperature will cause the change of refractive index of optical material, and then affect the imaging quality of optical system. The change of refractive index directly affects the propagation path of light in optical elements, thereby causing the shift of focal position of imaging system and resulting in imaging blur. In addition, the structural material of optical lens barrel will also expand or contract due to temperature change. This thermal expansion and contraction phenomenon causes thermal defocus of the image plane of the optical lens, so that the imaging camera cannot obtain a clear target image. Especially in high-precision measurement, the small change of imaging distance will cause defocus phenomenon at the lens image plane, and distance compensation means needs to be used for distance compensation to ensure clear imaging.

[0004] The athermalization design of imaging system plays a key role in solving these temperature-induced problems. The difficulty of athermalization design is closely related to the focal length, relative aperture, working wavelength range and matched spatial frequency of the system. Generally, the longer the focal length of the system, the more sensitive it is to the change of environmental temperature; the larger the relative aperture, the narrower the range of working environmental temperature that the system can tolerate; the wider the working wavelength range, the higher the matched spatial frequency, and the more difficult the athermalization design becomes.

[0005] One of the commonly used athermalization measures is the optical passive athermalization method. This method uses the thermal properties of various optical materials, reasonably allocates the optical power and temperature characteristics of the used lenses, and matches the thermal expansion coefficient of the lens structure material, so as to realize clear imaging of the system in a wide temperature range. This method has the advantages of relatively simple structure, small size, light weight, and high reliability.

[0006] For example, Chinese patent CN111796397A discloses a medium F number large field of view visible light athermalization optical system, which has a working wavelength of 450nm-700nm, a focal length of 130mm, an F number of 5.6, a field of view angle of 79°, a distortion value of 1%, and a spatial frequency of 1001p / mm. This design introduces high-order aspheric surfaces to realize athermalization design under large field of view, but lacks distance defocus compensation design under close-range imaging.

[0007] Similarly, Chinese patent CN209311769U discloses a small-F-number visible light athermalization optical system, the system focal length is 250mm, the F number is 1.78, the working waveband is 450nm~650nm, and the field of view angle is 1.2°. Although the system has a relatively narrow working waveband range and a low spatial frequency, and is relatively easy to realize athermalization, the distance defocus compensation design for close-range imaging is still lacking.

[0008] Furthermore, Chinese patent CN209842210U discloses a large-field-of-view athermalization visible light lens, the system focal length is 11.36mm, the relative space F / 4, the working spectrum is 450nm~850nm, and the spatial frequency is 145lp / mm. Since the focal length is very short, the athermalization design is relatively easy to realize, and each lens used by the lens is made of different materials, and the types and quantities are relatively large, most of which are rare glass materials. More importantly, in actual use, the actual imaging performance of the lens is greatly affected by the difference between the theoretical value and the actual value of the refractive index / dispersion coefficient of the material. The MTF at 145lp / mm is about 0.18, and the modulation degree is relatively low.

[0009] In summary, the prior art has made certain progress in realizing the athermalization design of the optical system, but there are still deficiencies in the distance defocus compensation design for close-range imaging, and further research and improvement are needed. SUMMARY

[0010] The purpose of the present application is to solve the problem of the prior art in the distance defocus compensation design for close-range imaging, and to provide a visible light athermalization optical system with a wide temperature range and a wide working spectrum.

[0011] In order to solve the deficiencies of the prior art, the present application provides the following technical solutions:

[0012] A visible light athermalization optical system with a wide temperature range and a wide working spectrum, comprising a front lens group and a rear lens group; the special feature is that:

[0013] The front lens group comprises six front lenses arranged in order from the object plane to the image plane; the first front lens is a positive focal power meniscus HZF88GT lens bent toward the image plane, the second front lens is a negative focal power meniscus HZF7LAGT lens bent toward the image plane, the third front lens is a positive focal power meniscus HFK95N lens bent toward the image plane, the fourth front lens is a negative focal power double-concave HZF7LAGT lens, the fifth front lens is a negative focal power meniscus HZF9B lens bent toward the image plane, and the sixth front lens is a positive focal power double-convex HZF9B lens.

[0014] The rear lens group comprises five rear lenses arranged in sequence from object plane to image plane, the first rear lens is a positive focal length double-convex HFK95N lens, the second rear lens is a negative focal length double-concave HZF7LAGT lens, the third rear lens is a positive focal length double-convex HZF88GT lens, the fourth rear lens is a negative focal length meniscus HFK95N lens bending towards the object plane, and the fifth rear lens is a negative focal length meniscus HZF9B lens bending towards the object plane.

[0015] The second rear lens and the third rear lens constitute a focusing lens group for internal focusing, and the distance from the fifth rear lens to the image plane is used for external focusing.

[0016] Further, the absolute values of the focal lengths of the first front lens, the second front lens, the third front lens, the fourth front lens, the fifth front lens, the sixth front lens, the first rear lens, the second rear lens, the third rear lens, the fourth rear lens and the fifth rear lens are respectively 0.007-0.0082, 0.01-0.02, 0.007-0.0082, 0.01-0.02, 0.001-0.0025, 0.01-0.022, 0.01-0.022, 0.01-0.03, 0.01-0.022, 0.0045-0.0065, 0.0025-0.0045.

[0017] Further, the intervals of the first front lens and the second front lens, the second front lens and the third front lens, the third front lens and the fourth front lens, the fourth front lens and the fifth front lens, the fifth front lens and the sixth front lens, the sixth front lens and the first rear lens, the first rear lens and the second rear lens, the second rear lens and the third rear lens, the third rear lens and the fourth rear lens, the fourth rear lens and the fifth rear lens are respectively 1, 2.32, 7.7, 1.4, 3.66, 20.67, 7.56-7.77, 2, 19.78-19.57, 4.56; all units are mm.

[0018] Further, the distance from the fifth rear lens to the image plane is 30mm-30.36mm.

[0019] Further, both surfaces of the six front lenses and the five rear lenses are spherical surfaces.

[0020] Further, thicknesses of the first front lens, the second front lens, the third front lens, the fourth front lens, the fifth front lens, the sixth front lens, the first rear lens, the second rear lens, the third rear lens, the fourth rear lens and the fifth rear lens are respectively 8.5-10.5, 4.5-7.5, 9-13, 4.5-7.5, 4.5-7.5, 8-10.5, 8-13, 4.5-7.5, 6-9.5, 4.5-7.5, 6-9.5; units are mm.

[0021] Further, the front lens group and the rear lens group are arranged in the aluminum lens barrel.

[0022] Compared with the prior art, the present application has the following beneficial effects:

[0023] (1) The visible light athermalization optical system of the present application has a wide temperature range and a wide working spectrum, and compensates for thermal defocus of the optical system at high and low temperatures by matching the refractive index coefficient, the dispersion coefficient and the thermal expansion coefficient of HZF88GT, HZF7LAGT, HFK95N and HZK9B, so that the imaging quality is ensured at a working temperature range of -40℃ to +60℃, and the thermal defocus compensation is not needed by using internal focusing means or external focusing means, and the imaging blur caused by temperature change is compensated by matching the thermal characteristics of the lens material and the lens barrel structure material, so that the reliability is high.

[0024] (2) The present application is a medium focal length, medium F number, wide spectrum imaging optical system, and has the characteristics of wide working wavelength, high resolution, high spatial frequency and wide working temperature.

[0025] (3) The lens surface used in the present application is a global surface, and all are common optical glass materials, which reduces the processing and detection difficulty and reduces the processing cost.

[0026] (4) The distortion of the present application is 2‰, which is a low distortion lens and can meet the high-precision measurement requirement.

[0027] (5) The present application realizes the imaging focusing from infinity to a close distance (50m) by the internal focusing (focusing lens group) and external focusing (moving the image plane to change the back intercept). The focusing mechanism is flexible and can adapt to different focusing application requirements. BRIEF DESCRIPTION OF DRAWINGS

[0028] Figure 1 is a schematic diagram of an optical path of an embodiment of a visible light athermalization optical system of the present application with a wide temperature range and a wide working spectrum.

[0029] Figure 1 The reference signs are explained as follows:

[0030] 01 - image plane; 1 - first front lens; 2 - second front lens; 3 - third front lens; 4 - fourth front lens; 5 - fifth front lens; 6 - sixth front lens; 7 - first rear lens; 8 - second rear lens; 9 - third rear lens; 10 - fourth rear lens; 11 - fifth rear lens; 110 - focusing group.

[0031] Figure 2 is the MTF (Modulation Transfer Function) plot of the embodiment of the present application at -40°C;

[0032] Figure 3 is the MTF plot of the embodiment of the present application at 22°C;

[0033] Figure 4 is the MTF plot of the embodiment of the present application at +60°C;

[0034] Figure 5 is the plot of the Longitudinal Spherical Aberration, Astigmatic Field Curves and Distortion of the embodiment of the present application at -40°C;

[0035] Figure 6 is the plot of the Longitudinal Spherical Aberration, Astigmatic Field Curves and Distortion of the embodiment of the present application at 22°C;

[0036] Figure 7 is the plot of the Longitudinal Spherical Aberration, Astigmatic Field Curves and Distortion of the embodiment of the present application at +60°C;

[0037] Figure 8 is the internal focusing compensation MTF plot of the embodiment of the present application at -40°C for a close distance of 50m;

[0038] Figure 9 is the internal focusing compensation MTF plot of the embodiment of the present application at 22°C for a close distance of 50m;

[0039] Figure 10 is the internal focusing compensation MTF plot of the embodiment of the present application at +60°C for a close distance of 50m;

[0040] Figure 11 is the external focusing compensation MTF plot of the embodiment of the present application at -40°C for a close distance of 50m;

[0041] Figure 12 is the external focusing compensation MTF plot of the embodiment of the present application at 22°C for a close distance of 50m;

[0042] Figure 13 is the external focusing compensation MTF plot of the embodiment of the present application at +60°C for a close distance of 50m. DETAILED DESCRIPTION

[0043] The present application is further described below in conjunction with the accompanying drawings and exemplary embodiments.

[0044] According to the ideal thin lens theory, in the process of optical passive athermalization design of the visible light system, each lens element needs to meet the following three principles: power distribution, achromatism and athermalization. The specific description is as follows:

[0045] Power distribution:

[0046]

[0047] In the formula, Φ is the total power of the system, Φ i is the power of each lens group, h i is the incident height of the first paraxial ray on each lens group;

[0048] Achromatism

[0049]

[0050] In the formula, C i is the chromatic aberration coefficient of each lens material, and λ is the wavelength;

[0051] Athermalization:

[0052]

[0053] In the formula, T i is the thermal difference coefficient of each lens material, and T is the thermal difference coefficient of the system;

[0054] The chromatic aberration coefficient C and the thermal difference coefficient T can be expressed as:

[0055]

[0056]

[0057] In the formula, v is the Abbe number of each lens material; is the difference between the refractive indices of each lens material at the edge wavelengths λ1 and λ2, n λc is the refractive index at the central wavelength λ c , and n represents the refractive index of the lens material at a specific wavelength, dn represents the small change in the refractive index of the lens material, and α is the thermal expansion coefficient of the material.

[0058] The distance defocus compensation condition provides a method for adjusting the spacing of the optical system to refocus when the object distance changes by calculating the new image distance and the defocus amount, thereby ensuring the clarity of the image and the stability of the system, which is as follows:

[0059]

[0060] where l' is the new image distance (i.e. the adjusted image point position), l is the object distance (i.e. the distance of the object to the lens), f' is the focal length of the lens, and Δl' is the defocus, i.e. the difference between the new image distance l' and the focal length f'.

[0061] Referring to Figure 1 A visible light athermalization optical system with wide temperature range and wide working spectrum, which adopts a complex double-Gaussian primary imaging structure, comprises a front lens group and a rear lens group.

[0062] The front lens group comprises six front lenses arranged in sequence from the object plane to the image plane 01; the first front lens 1 is a positive focal length meniscus HZF88GT lens bent towards the image plane 01, the second front lens 2 is a negative focal length meniscus HZF7LAGT lens bent towards the image plane 01, the third front lens 3 is a positive focal length meniscus HFK95N lens bent towards the image plane 01, the fourth front lens 4 is a negative focal length double-concave HZF7LAGT lens, the fifth front lens 5 is a negative focal length meniscus HZF9B lens bent towards the image plane 01, and the sixth front lens 6 is a positive focal length double-convex HZF9B lens.

[0063] The rear lens group comprises five rear lenses arranged in sequence from the object plane to the image plane 01; the first rear lens 7 is a positive focal length double-convex HFK95N lens, the second rear lens 8 is a negative focal length double-concave HZF7LAGT lens, the third rear lens 9 is a positive focal length double-convex HZF88GT lens, the fourth rear lens 10 is a negative focal length meniscus HFK95N lens bent towards the object plane, and the fifth rear lens 11 is a negative focal length meniscus HZF9B lens bent towards the object plane.

[0064] The second rear lens 8 and the third rear lens 9 constitute a focusing lens group 110 for internal focusing; changing the interval of the image plane 01 is used for external focusing.

[0065] The interval of the first front lens 1 and the second front lens 2, the second front lens 2 and the third front lens 3, the third front lens 3 and the fourth front lens 4, the fourth front lens 4 and the fifth front lens 5, the fifth front lens 5 and the sixth front lens 6, the sixth front lens 6 and the first rear lens 7, the first rear lens 7 and the second rear lens 8, the second rear lens 8 and the third rear lens 9, the third rear lens 9 and the fourth rear lens 10, and the fourth rear lens 10 and the fifth rear lens 11 is 1mm, 2.32mm, 7.7mm, 1.4mm, 3.66mm, 20.67mm, 7.56mm-7.77mm, 2mm, 19.78mm-19.57mm, and 4.56mm, respectively. The distance from the fifth rear lens 11 to the image plane 01 is 30mm-30.36mm, and the interval is changed for external focusing and changing back focus. Therefore, clear imaging under close range can be realized by internal focusing and external focusing, and in actual use, one of the two can be selected according to application requirements.

[0066] The lens parameters are shown in Table 1:

[0067] Table 1

[0068]

[0069]

[0070] The focal length of the visible light athermalization optical system is 135mm, the F number is 4, the field of view angle is 16.82*11.25, the working spectral range is 450nm-800nm, it is suitable for a high-resolution visible light camera with a resolution of 12000*8000 and a pixel size of 3.45um, the adaptable working temperature range is-40℃-+60℃, the total length of the system is 186mm, and the nearest imaging distance that can be realized is 50m.

[0071] The parameters of HZF88GT, HZF7LAGT, HFK95N and HZK9B used in the application are shown in Table 2:

[0072] Table 2

[0073]

[0074] HZF88GT and HZF7LAGT can be used as chromatic aberration correction elements, and HZF88GT, HZF7LAGT, HFK95N and HZK9B can be used as aberration correction elements in combination of positive and negative focal lengths.

[0075] HZF88GT and HZF9B have the thermal difference characteristics of low thermal expansion coefficient and positive refractive index temperature coefficient, HFK95N and HZF7LAGT have the thermal difference characteristics of high thermal expansion coefficient and negative refractive index temperature coefficient, and the four material combinations can realize the athermal design under the premise that the lens barrel material is aluminum.

[0076] In order to meet the test requirements of close-range imaging, the defocus amount introduced in close-range imaging is determined according to the distance defocus compensation condition. The close-range imaging can be realized by internal focusing of the focusing lens group 110, and the focusing amount is +0.21mm; or external focusing by moving the image plane 01 (camera), and the moving amount is +0.36mm.

[0077] Figures 2-4 For the MTF curve of the embodiment of the present application under a wide temperature range, the meridional / tangential MTF of the maximum field of view outside the axis at low temperature (-40 DEG C) is better than 0.36, the meridional / tangential MTF of the maximum field of view outside the axis at normal temperature (22 DEG C) is better than 0.43, and the meridional / tangential MTF of the maximum field of view outside the axis at high temperature (+60 DEG C) is better than 0.42, close to the diffraction limit.

[0078] Figures 5-7 For the spherical aberration, field curvature and distortion figure of the embodiment of the present application under a wide temperature range, the distortion value is less than or equal to 1.6‰, the residual aberration amount is small, the distortion of the full field of view is small, and the imaging quality is good, which can meet the measurement requirements at different distances.

[0079] Figures 8-10 The MTF compensation curve figures of the embodiment of the present application at -40 DEG C, 22 DEG C and +60 DEG C for close-range 50m are shown in the following table: Figure 8 In the high frequency (above 145 cycles / mm), most of the MTFs still maintain a high modulation value, the meridional / tangential MTF of the maximum field of view outside the axis at low temperature (-40 DEG C) is better than 0.31, which indicates that the imaging quality of the embodiment of the present application at low temperature is good. Figure 9 In the high frequency, all the MTFs have consistent performance, the meridional / tangential MTF of the maximum field of view outside the axis at room temperature is better than 0.31, which indicates that the embodiment of the present application has good modulation contrast and consistency at room temperature. Figure 10 Compared with low temperature and room temperature, the MTFs in the high temperature are slightly improved, the meridional / tangential MTF of the maximum field of view outside the axis at high temperature (+60 DEG C) is better than 0.34, which indicates that the modulation contrast of the embodiment of the present application at high temperature is slightly improved. The MTF curves of the embodiment of the present application at different temperatures show that temperature has a certain influence on the imaging quality, but the overall performance is stable. Through internal focusing (moving the focusing lens group 110 by +0.21mm), the embodiment of the present application can effectively compensate the imaging requirements from infinity to 50m at different temperatures, and has good focusing ability and adaptability.

[0080] Figures 11-13 The MTF compensation curves of the embodiment of the application at -40℃, 22℃ and +60℃ for the outer focusing at 50m; Figure 11 Most of the MTFs in the embodiment of the application maintain a high modulation value at high frequencies (above 145 cycles / mm), and the meridional / tangential MTF of the maximum field of view outside the axis is better than 0.34 at low temperature (-40℃), indicating that the imaging quality of the embodiment of the application at low temperature is good; Figure 12 All the MTFs in the embodiment of the application perform consistently at high frequencies, and the meridional / tangential MTF of the maximum field of view outside the axis is better than 0.34 at room temperature, indicating that the embodiment of the application has good modulation contrast and consistency at room temperature; Figure 13 The MTFs in the embodiment of the application are slightly improved compared with those at low temperature and room temperature, and the meridional / tangential MTF of the maximum field of view outside the axis is better than 0.38 at high temperature (+60℃), indicating that the modulation contrast of the embodiment of the application at high temperature is slightly improved. Through the adjustment of outer focusing (moving the image plane by +0.36mm), the embodiment of the application can effectively compensate for the imaging requirements from infinity to 50m at various temperatures, showing good focusing ability and adaptability.

Claims

1. A wide temperature range and wide working spectrum visible light athermalization optical system comprising a front lens group and a rear lens group; characterized in that: the front lens group comprises six front lenses arranged in order from the object plane to the image plane (01); the first front lens (1) is a positive focal power meniscus HZF88GT lens bent towards the image plane (01), the second front lens (2) is a negative focal power meniscus HZF7LAGT lens bent towards the image plane (01), the third front lens (3) is a positive focal power meniscus HFK95N lens bent towards the image plane (01), the fourth front lens (4) is a negative focal power double-concave HZF7LAGT lens, the fifth front lens (5) is a negative focal power meniscus HZK9B lens bent towards the image plane (01), and the sixth front lens (6) is a positive focal power double-convex HZK9B lens; the rear lens group comprises five rear lenses arranged in order from the object plane to the image plane (01), the first rear lens (7) is a positive focal power double-convex HFK95N lens, the second rear lens (8) is a negative focal power double-concave HZF7LAGT lens, the third rear lens (9) is a positive focal power double-convex HZF88GT lens, the fourth rear lens (10) is a negative focal power meniscus HFK95N lens bent towards the object plane, and the fifth rear lens (11) is a negative focal power meniscus HZK9B lens bent towards the object plane; the second rear lens (8) and the third rear lens (9) constitute a focusing lens group (110) for internal focusing; and the distance from the fifth rear lens (11) to the image plane (01) is used for external focusing.

2. The wide temperature range and wide working spectrum visible light athermalization optical system according to claim 1, characterized in that: the absolute values of the focal powers of the first front lens (1), the second front lens (2), the third front lens (3), the fourth front lens (4), the fifth front lens (5), the sixth front lens (6), the first rear lens (7), the second rear lens (8), the third rear lens (9), the fourth rear lens (10), and the fifth rear lens (11) are 0.007-0.0082, 0.01-0.02, 0.007-0.0082, 0.01-0.02, 0.001-0.0025, 0.01-0.022, 0.01-0.022, 0.01-0.03, 0.01-0.022, 0.0045-0.0065, and 0.0025-0.0045, respectively.

3. The wide temperature range and wide working spectrum visible light athermalization optical system according to claim 2, characterized in that: ​ ​ ​ ​ The interval of the first front lens (1) and the second front lens (2), the second front lens (2) and the third front lens (3), the third front lens (3) and the fourth front lens (4), the fourth front lens (4) and the fifth front lens (5), the fifth front lens (5) and the sixth front lens (6), the sixth front lens (6) and the first rear lens (7), the first rear lens (7) and the second rear lens (8), the second rear lens (8) and the third rear lens (9), the third rear lens (9) and the fourth rear lens (10), the fourth rear lens (10) and the fifth rear lens (11) is 1, 2.32, 7.7, 1.4, 3.66, 20.67, 7.56-7.77, 2, 19.78-19.57, 4.56 respectively; the unit is mm.

4. The visible light athermal optical system of wide temperature range and wide working spectrum according to claim 3, characterized in that: The distance from the fifth rear lens (11) to the image plane (01) is 30mm-30.36mm.

5. The visible light athermal optical system of wide temperature range and wide working spectrum according to any one of claims 1-4, characterized in that: Both surfaces of the six front lenses and the five rear lenses are spherical surfaces.

6. The visible light athermal optical system of wide temperature range and wide working spectrum according to claim 5, characterized in that: The thickness of the first front lens (1), the second front lens (2), the third front lens (3), the fourth front lens (4), the fifth front lens (5), the sixth front lens (6), the first rear lens (7), the second rear lens (8), the third rear lens (9), the fourth rear lens (10) and the fifth rear lens (11) is 8.5-10.5, 4.5-7.5, 9-13, 4.5-7.5, 4.5-7.5, 8-10.5, 8-13, 4.5-7.5, 6-9.5, 4.5-7.5, 6-9.5 respectively; the unit is mm.

7. The visible light athermal optical system of wide temperature range and wide working spectrum according to claim 1, characterized in that: The front lens group and the rear lens group are arranged in an aluminum lens barrel.

Images