A long working distance long back focal high efficiency zoom lens for projection

Abstract

The application provides a long-working-distance long-back-focus high-efficiency zoom lens for projection, comprising: a first lens group with negative optical power, a second lens group with positive optical power, a third lens group with positive optical power, a galvanometer, a light splitting device and an imaging surface arranged in sequence; air spaces capable of moving along the optical axis direction are arranged between the first lens group and the second lens group, between the second lens group and the third lens group and between the third lens group and the galvanometer; the ratio of the focal length of the first lens group to the focal length of the second lens group ranges from 0.15 to 0.35; the ratio of the focal length of the first lens group to the focal length of the third lens group ranges from 1.4 to 1.6; the second lens group, the third lens group, the galvanometer, the light splitting device and the imaging surface are all made of glass material. The application can fill the vacancy that the DLP illumination system with long-focus setting is difficult to match the optical zoom lens, and solve the problems of low relative luminance of the edge field of view of the zoom projection objective lens, insufficient image quality and unstable system architecture.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of lens design, in particular to a long working distance and long back focal high-efficiency zoom lens for projection. BACKGROUND

[0002] Fixed specification fixed focus lenses are only suitable for specific application scenarios, and different specifications of fixed focus lenses need to be replaced as the application scenarios change, and reserving multiple specifications of fixed focus lenses means that more design, material, storage and other costs need to be invested. Once the lens is assembled with the whole machine, the process of changing the lens again is relatively cumbersome.

[0003] There are few existing zoom solutions suitable for DLP projection systems, and due to cost considerations, the illumination structure of the DLP projection system mostly uses an RTIR prism to realize light path turning. The high refractive index of the RTIR prism leads to an increase in the optical path, which lengthens the back focal length of the imaging system, increasing the difficulty of lens design. If the optical zoom requirement is added on this basis, the lens design becomes more difficult. SUMMARY

[0004] In order to overcome the shortcomings of the prior art, the purpose of the present application is to provide a long working distance and long back focal high-efficiency zoom lens for projection.

[0005] To achieve the above-mentioned purpose, the present application provides the following solutions:

[0006] A long working distance and long back focal high-efficiency zoom lens for projection comprises: a first lens group with negative focal power, a second lens group with positive focal power, a third lens group with positive focal power, a galvanometer, a light splitting device and an imaging surface arranged in sequence;

[0007] An air gap capable of displacement along the optical axis direction is arranged between the first lens group and the second lens group, between the second lens group and the third lens group, and between the third lens group and the galvanometer; the ratio of the focal length of the first lens group to the focal length of the second lens group ranges from 0.15 to 0.35; the ratio of the focal length of the first lens group to the focal length of the third lens group ranges from 1.4 to 1.6; the second lens group, the third lens group, the galvanometer, the light splitting device and the imaging surface are all made of glass material.

[0008] Preferably, the first lens group comprises a first lens, a second lens and a third lens arranged in sequence;

[0009] The air gap is arranged between the third lens and the second lens group; the first lens is an aspherical lens; the refractive index of the first lens ranges from 1.4 to 1.6; the Abbe number of the first lens ranges from 35 to 75; the first lens is made of plastic material.

[0010] Preferably, the second lens group comprises a fourth lens, a fifth lens, a diaphragm, a sixth lens and a seventh lens arranged in sequence.

[0011] The seventh lens is provided with the air spacing between the third lens group.

[0012] Preferably, the fourth lens and the fifth lens are opposite in bending direction; the Abbe number of the fourth lens and the fifth lens is greater than a preset threshold value; the fourth lens and the fifth lens both have positive focal power; the sixth lens and the seventh lens are cemented lenses with negative focal power.

[0013] Preferably, the third lens group comprises an eighth lens and a ninth lens arranged in sequence.

[0014] The ninth lens is provided with the air spacing between the galvanometer; the eighth lens and the ninth lens both have positive focal power; the ninth lens is an aspherical lens; the refractive index of the ninth lens ranges from 1.5 to 1.7; the Abbe number of the ninth lens ranges from 40 to 80.

[0015] Preferably, further comprising a protective glass.

[0016] The protective glass is arranged between the light splitting device and the imaging surface.

[0017] According to the specific embodiments of the present application, the following technical effects are provided:

[0018] The present application provides a long working distance long back focus high efficiency zoom lens for projection, comprising: a first lens group with negative focal power, a second lens group with positive focal power, a third lens group with positive focal power, a galvanometer, a light splitting device and an imaging surface arranged in sequence; the air spacing capable of displacement along the optical axis direction is arranged between the first lens group and the second lens group, between the second lens group and the third lens group, and between the third lens group and the galvanometer; the ratio of the focal length of the first lens group to the focal length of the second lens group ranges from 0.15 to 0.35; the ratio of the focal length of the first lens group to the focal length of the third lens group ranges from 1.4 to 1.6; the second lens group, the third lens group, the galvanometer, the light splitting device and the imaging surface are all made of glass material. The present application can fill the vacancy that the DLP illumination system with long focus setting is difficult to match the optical zoom lens, solve the problems of low relative luminance of the edge field of view of the zoom projection objective lens, insufficient image quality, unstable system architecture and the like. BRIEF DESCRIPTION OF DRAWINGS

[0019] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings needed in the embodiments. Obviously, the drawings described below are only some embodiments of the present application, and for those skilled in the art, other drawings can also be obtained from these drawings without creative labor.

[0020] Figure 1 The lens structure schematic diagram provided for the embodiment of the present application;

[0021] Figure 2 The zoom lens group displacement schematic diagram provided for the embodiment of the present application;

[0022] Figure 3 The MTF schematic diagram of the zoom system in the wide-angle state provided for the embodiment of the present application;

[0023] Figure 4 The MTF schematic diagram of the zoom system in the long-focus state provided for the embodiment of the present application;

[0024] Figure 5 The relative luminance schematic diagram of the zoom system in the wide-angle state provided for the embodiment of the present application;

[0025] Figure 6 The relative luminance schematic diagram of the zoom system in the long-focus state provided for the embodiment of the present application;

[0026] Explanation of reference signs:

[0027] 1-first lens group, 2-second lens group, 3-third lens group, 4-diaphragm, 5-galvanometer, 6-splitting device, 7-protective glass, 8-imaging surface, P1-first lens, G2-second lens, G3-third lens, G4-fourth lens, G5-fifth lens, G6-sixth lens, G7-seventh lens, G8-eighth lens, GM9-ninth lens. DETAILED DESCRIPTION

[0028] The technical solutions in the embodiments of the present application will be described clearly and completely below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only some embodiments of the present application, not all embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor are within the scope of protection of the present application.

[0029] The purpose of the present application is to provide a long working distance long back focal high efficiency zoom lens for projection, which can fill the vacancy of the DLP illumination system with long focal setting difficult to match the optical zoom lens, solve the problems of low relative luminance of the edge field of view of the zoom projection objective lens, insufficient image quality, unstable system architecture, etc.

[0030] In order to make the above objectives, features and advantages of the present application more obvious and easy to understand, the present application will be further described in detail below with reference to the drawings and specific embodiments.

[0031] Figure 1 The schematic diagram of the lens structure provided by the embodiment of the present application is shown in the figure, and the present application provides a long working distance long back focal high efficiency zoom lens for projection, which comprises: a first lens group 1 with negative optical power, a second lens group 2 with positive optical power, a third lens group 3 with positive optical power, a galvanometer 5, a light splitting device 6, a protective glass 7 and an imaging surface 8 arranged in sequence. Figure 1

[0032] The air spacing capable of being displaced along the optical axis direction is arranged between the first lens group 1 and the second lens group 2, between the second lens group 2 and the third lens group 3 and between the third lens group 3 and the galvanometer 5; the ratio of the focal length of the first lens group 1 to the focal length of the second lens group 2 ranges from 0.15 to 0.35; the ratio of the focal length of the first lens group 1 to the focal length of the third lens group 3 ranges from 1.4 to 1.6; the second lens group 2, the third lens group 3, the galvanometer 5, the light splitting device 6 and the imaging surface 8 are all made of glass material.

[0033] Specifically, the first lens P1 is made of plastic material, the second lens G2, the third lens G3, the fourth lens G4, the fifth lens G5, the sixth lens G6, the seventh lens G7, the eighth lens G8 and the ninth lens GM9, the light splitting device 6 and the protective glass 7 are all made of glass material. The first lens group 1 with negative optical power is composed of the first lens P1 with negative optical power and the second lens G2 / third lens G3 with positive optical power. The second lens group 2 with positive optical power is composed of the fourth lens G4 with positive optical power, the fifth lens G5 with positive optical power and the sixth lens G6 / seventh lens G7 (cemented lens) with negative optical power. The third lens group 3 with positive optical power is composed of the eighth lens G8 with positive optical power and the ninth lens GM9 with positive optical power.

[0034] ​Preferably, the first lens group 1 comprises a first lens P1, a second lens G2 and a third lens G3 arranged in sequence; the third lens G3 and the second lens group 2 are provided with the air gap; the first lens P1 is an aspherical lens; the refractive index of the first lens P1 ranges from 1.4 to 1.6; the Abbe number of the first lens P1 ranges from 35 to 75; the first lens P1 is made of plastic material. The second lens group 2 comprises a fourth lens G4, a fifth lens G5, a diaphragm 4, a sixth lens G6 and a seventh lens G7 arranged in sequence; the seventh lens G7 and the third lens group 3 are provided with the air gap. The fourth lens G4 and the fifth lens G5 are opposite in bending direction; the Abbe numbers of the fourth lens G4 and the fifth lens G5 are greater than a preset threshold value; the fourth lens G4 and the fifth lens G5 both have positive focal power; the sixth lens G6 and the seventh lens G7 are cemented lenses with negative focal power. The third lens group 3 comprises an eighth lens G8 and a ninth lens GM9 arranged in sequence; the ninth lens GM9 and the galvanometer 5 are provided with the air gap; the eighth lens G8 and the ninth lens GM9 both have positive focal power; the ninth lens GM9 is an aspherical lens; the refractive index of the ninth lens GM9 ranges from 1.5 to 1.7; the Abbe number of the ninth lens GM9 ranges from 40 to 80.

[0035] The parameters in the embodiment are shown in Table 1 and Table 2, wherein the P1 and GM9 lenses are both aspherical lenses;

[0036] 1. The ratio of the focal length f1 of the first lens group 1 to the focal length f2 of the second lens group 2 of the objective lens system is about 0.15 < |f1 / f2| < 0.35;

[0037] 2. The ratio of the focal length f1 of the first lens group 1 to the focal length f3 of the third lens group 3 of the objective lens system is about 1.4 < |f1 / f3| < 1.6;

[0038] 3. The ratio of the effective focal length fT of the telephoto state to the effective focal length fW of the wide-angle state of the objective lens system is 1 < fT / fW < 1.4;

[0039] 4. The ratio of the total optical length TTLT of the telephoto state to the total optical length TTLW of the wide-angle state of the objective lens system is 0.9 < TTLT / TTLW < 1.3;

[0040] 5. In the objective lens system, the air gap length between the third lens G3 and the fourth lens G4, the air gap length between the seventh lens G7 and the eighth lens G8, and the air gap length between the ninth lens GM9 and the galvanometer 5 are all changeable along the optical axis;

[0041] 6. The first lens P1 has a refractive index n1 and an Abbe number v1, where 1.4 < n1 < 1.6 and 35 < v1 < 75;

[0042] 7. The ninth lens GM9 has a refractive index n9 and an Abbe number v9, where 1.5 < n9 < 1.7 and 40 < v9 < 80;

[0043] 8. The total back focal length, where 3 mm < total air gap < 10 mm and 10 mm < total glass thickness < 20 mm.

[0044] Table 1. Specific parameters of the objective system

[0045]

[0046]

[0047] Table 2. Coefficients of the aspherical lenses P1 and GM9

[0048]

[0049]

[0050] As shown in the table 3, the specific values of the air gap of the zoom lens group are shown in the table 3. Figure 2

[0051] Table 3. Variable air gap values of the zoom lens

[0052]

[0053] Optionally, the MTF (Modulation Transfer Function) index is the most accurate and scientific evaluation standard for the lens. The vertical coordinate is the contrast, and the closer to 1, the better the imaging of the lens. The horizontal coordinate represents the resolution, with the unit of log / mm. The pixel size of the image source used in the embodiment of the application is 5.4 um, and the corresponding design resolution is 93 lp / mm. The projection lens generally requires that the MTF value of each field of view reaches 0.3 or above at the design resolution, and as shown in the table 4, the MTF values of the optical zoom focal length in the embodiment of the application are all above 0.7, which has excellent imaging quality. Figures 3-4

[0054] ​​Furthermore, relative illuminance refers to the ratio of illuminance at different coordinate points on the image plane to the illuminance at the center point. The vertical axis represents the normalized illuminance value, and the horizontal axis represents the field of view of the lens. Under the same conditions, a smooth transition in the relative illuminance curves across different fields of view indicates uniform illuminance within the projection frame, and the closer the relative illuminance value of each field of view is to 1, the higher the final projection brightness. Figures 5-6 As shown, this embodiment exhibits high image plane illumination uniformity, which also suggests that the system possesses high efficiency and high brightness. The principle behind high brightness lies in the following: Numerical aperture = D (entrance pupil diameter) / f (focal length). With the focal length remaining constant, a larger numerical aperture means a larger entrance pupil diameter. In optics, the entrance pupil represents the light-gathering port. The larger the entrance pupil, the greater the light energy that can be received, and therefore the higher the brightness.

[0055] The projection lens system in this embodiment has the following features:

[0056] 1. The zoom objective lens system is composed of a first lens group 1 with negative optical power, a second lens group 2 with positive optical power, and a third lens group 3 with positive optical power. An air gap that can be displaced along the optical axis is provided between the lens groups. Together, they form a reverse telephoto objective lens that can achieve optical zoom and can be adapted to DLP projection illumination systems with long back focal length.

[0057] 2. Two cemented doublet lenses are placed before and after aperture 4. The combination of low refractive index and high Abbe number materials with high refractive index and high Abbe number materials effectively reduces the second-order spectrum of the system.

[0058] 3. The second lens group 2 consists of two positive power meniscus lenses with opposite curvature directions and significantly different Abbe constants, and a cemented lens with negative power. This effectively reduces the incident angle of light in the system and corrects axial chromatic aberration and transverse chromatic aberration over a large field of view. It also helps to reduce the variation in the aperture of the intermediate aperture 4 in the second lens group 2, ensuring high brightness and high efficiency of the lens system.

[0059] 4. An aspherical lens GM9 is placed in front of the image source to provide maximum aberration correction for the system and ensure that the incident angle of the principal rays in each field of view is perfectly matched with the image source, thereby improving the image quality and efficiency of the entire imaging system.

[0060] 5. In the implementation method, the optical lens satisfies the following condition:

[0061] 0.8 <IH / EPND<1.1 (1)

[0062] Wherein, EPND represents the aperture of the optical lens, and IH represents the actual half-image height of the optical lens.

[0063] When the conditional expression (1) is satisfied, a reasonable balance between a large light throughput and a large imaging surface 8 under the zoom lens specification can be achieved, and the overall projection brightness can be effectively improved.

[0064] 6. In the embodiments, the optical lens satisfies the following conditional expression:

[0065] CRA< 2° (2)

[0066] Wherein, CRA represents the chief ray angle of incidence of the optical lens on the imaging surface 8.

[0067] When the conditional expression (2) is satisfied, the DMD chip can be well matched, and a good projection effect can be achieved.

[0068] In the specification, each embodiment is described in a progressive manner, and each embodiment focuses on the differences from other embodiments. The same or similar parts of each embodiment can be mutually referred to.

[0069] The principles and embodiments of the present application are described herein by using specific examples. The above description of the embodiments is only used to help understand the method and core idea of the present application. Meanwhile, for those skilled in the art, the specific embodiments and application scope can be changed according to the idea of the present application. In summary, the content of the specification should not be understood as a limitation of the present application.

Claims

1. A long working distance long back focal high efficiency zoom lens for projection, characterized in that, The zoom lens comprises a first lens group with negative focal power, a second lens group with positive focal power, a third lens group with positive focal power, a galvanometer, a light splitting device and an imaging surface; the first lens group is composed of a first lens, a second lens and a third lens arranged in sequence; the first lens has negative focal power, and the second lens and the third lens are cemented lenses with positive focal power; the second lens group is composed of a fourth lens, a fifth lens, a diaphragm, a sixth lens and a seventh lens arranged in sequence; the fourth lens and the fifth lens both have positive focal power; the sixth lens and the seventh lens are cemented lenses with negative focal power; the third lens group is composed of an eighth lens and a ninth lens arranged in sequence; the eighth lens and the ninth lens both have positive focal power; An air gap capable of moving along the optical axis direction is arranged between the first lens group and the second lens group, between the second lens group and the third lens group and between the third lens group and the galvanometer; the ratio of the focal length of the first lens group to the focal length of the second lens group ranges from 0.15 to 0.35; the ratio of the focal length of the first lens group to the focal length of the third lens group ranges from 1.4 to 1.6; the second lens group, the third lens group, the galvanometer, the light splitting device and the imaging surface are all made of glass material; the zoom lens has nine lenses with focal power. The air gap is arranged between the third lens and the second lens group; the first lens is a non-spherical lens; the refractive index of the first lens ranges from 1.4 to 1.6; the Abbe number of the first lens ranges from 35 to 75; the first lens is made of plastic material.

2. The long working distance long back focal high efficiency zoom lens for projection according to claim 1, wherein, The air gap is arranged between the seventh lens and the third lens group.

3. The long working distance long back focal high efficiency zoom lens for projection according to claim 1, wherein, The fourth lens and the fifth lens have opposite bending directions.

4. The long working distance long back focal high efficiency zoom lens for projection according to claim 3, characterized in that, The air gap is arranged between the ninth lens and the galvanometer; the ninth lens is a non-spherical lens; the refractive index of the ninth lens ranges from 1.5 to 1.7; the Abbe number of the ninth lens ranges from 40 to 80.

5. The long working distance long back focal high efficiency zoom lens for projection according to claim 1, wherein, The zoom lens further comprises a protective glass; 6. The long working distance long back focal high efficiency zoom lens for projection according to claim 1, wherein, The protective glass is arranged between the light splitting device and the imaging surface. ​

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