A projection lens and apparatus
By setting a removable flat glass structure in the projection lens, the optical path is changed, which solves the problem of focusing instability of the projection lens when no motor is used, and achieves stable focusing performance and high-quality imaging, replacing the traditional motor drive method.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Utility models(China)
- Current Assignee / Owner
- SENWAYLIGHT TECH (SHENZHEN) CO LTD
- Filing Date
- 2025-07-31
- Publication Date
- 2026-08-04
AI Technical Summary
Existing projection lenses suffer from issues such as backlash, insensitive focus point recognition, and slow focusing speed during the focusing process, making it difficult to achieve stable and clear imaging, especially when a motor is not required for focusing.
By setting a first flat glass, a first lens assembly, and a second flat glass in the first component of the projection lens, and designing that at least one flat glass can be extracted from the first component, the optical path in the optical path can be changed by extracting the flat glass, thereby achieving focus displacement and replacing the traditional motor drive method.
It achieves focusing by adjusting the lens without using a motor, solving the problems of complex structure, high cost, easy damage and power consumption, and obtaining stable focusing performance and good image quality.
Smart Images
Figure CN224594906U_ABST
Abstract
Description
Technical Field
[0001] This application belongs to the field of machine vision, and more specifically, relates to a projection lens and device. Background Technology
[0002] In the field of machine vision, the distance of the observed objects varies. The projection lens needs to be moved along the entire axis or along the axis of some components to achieve focus, so that objects at different working distances can be clearly imaged at the DMD (Digital Light Processing).
[0003] In certain scenarios, only a fixed, specific distance needs to be clearly imaged. Under normal circumstances, motor focusing is used. When focusing, the motor needs to go beyond the point of sharpest focus and then move back. This process will produce a backlash, which needs to be compensated for, and the inconsistency in focusing will affect the focusing effect. Summary of the Invention
[0004] The purpose of this application is to provide a projection lens and device that can achieve focusing by adjusting the lens without using a motor.
[0005] In a first aspect, embodiments of this application provide a projection lens including a light-emitting chip; a first component and a second component are sequentially arranged along the light-emitting direction of the light-emitting chip; the second component includes a second lens assembly; the first component includes a first flat glass, a first lens assembly, and a second flat glass sequentially arranged along the light-emitting direction of the light-emitting chip;
[0006] At least one of the first flat glass and the second flat glass is used to be extracted from the first component to achieve focus shift of the projection lens.
[0007] Furthermore, the light-emitting chip is a digital micromirror device; the light-emitting direction of the digital micromirror device is provided with a protective glass and a prism equivalent plate in sequence.
[0008] Furthermore, the first component also includes an aperture; the aperture is disposed on the rear side of the second flat glass along the light emission direction of the light-emitting chip.
[0009] Furthermore, the first lens assembly includes a first spherical positive power lens, a second spherical positive power lens, a third spherical positive power lens, a fourth spherical negative power lens, and a fifth spherical positive power lens arranged sequentially along the light emission direction of the light-emitting chip.
[0010] Furthermore, the second lens assembly includes a sixth spherical positive power lens, a seventh spherical negative power lens, an eighth spherical negative power lens, and a ninth spherical positive power lens arranged sequentially along the light emission direction of the light-emitting chip.
[0011] Furthermore, the seventh spherical negative power lens is a biconcave lens, and the eighth spherical negative power lens is a negative meniscus lens; the edges of the concave surfaces of the seventh and eighth spherical negative power lenses are in contact.
[0012] Furthermore, the fourth spherical negative power lens is a biconcave lens; the fifth spherical positive power lens is a plano-convex lens; one concave surface of the fourth spherical negative power lens and the convex surface of the fifth spherical positive power lens are bonded together; the refractive index of the fourth spherical negative power lens is greater than or equal to 1.7, and the Abbe number is less than or equal to 30; the refractive index of the fifth spherical positive power lens is less than or equal to 1.65, and the Abbe number is greater than or equal to 60.
[0013] Furthermore, the first spherical positive power lens is a positive meniscus lens, the second spherical positive power lens is a biconvex lens, and the third spherical positive power lens is a plano-convex lens; the plane of the third spherical positive power lens contacts the edge of the other concave surface of the fourth spherical negative power lens; the convex surface of the third spherical positive power lens is close to one of the convex surfaces of the second spherical positive power lens; and the convex surface of the first spherical positive power lens is close to the other convex surface of the second spherical positive power lens.
[0014] Furthermore, the sixth spherical positive power lens is a biconvex lens; the ninth spherical positive power lens is a plano-convex lens; the plane of the ninth spherical positive power lens is close to the convex surface of the eighth spherical negative power lens.
[0015] Secondly, this application provides a projection device, including the aforementioned projection lens.
[0016] This application provides a projection lens and device. By incorporating a first flat glass, a first lens assembly, and a second flat glass in a first component of the projection lens, and designing a structure where at least one flat glass can be extracted from the first component, the extraction of the flat glass alters the optical path, thereby achieving focus shift of the projection lens. Thus, this application embodiment can achieve focusing by adjusting the lens without using a motor. This application embodiment replaces the traditional motor-driven method, eliminating the need for a motor and related drive and transmission structures, thereby solving the problems of complex structure, high cost, easy wear and tear, and high power consumption associated with using motors in traditional technologies. Attached Figure Description
[0017] To more clearly illustrate the technical solutions in the embodiments of this application, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.
[0018] Figure 1 This is a schematic diagram of the projection lens.
[0019] Figure 2 This is a schematic diagram of the structure of the first component.
[0020] Figure 3 This is a schematic diagram of the second component.
[0021] Figure 4 A schematic diagram of the light path when the projection lens is pulled out of the first flat glass for focusing.
[0022] Figure 5 A schematic diagram of the light path when the projection lens is pulled out of the second flat glass for focusing.
[0023] Figure 6 This is a schematic diagram of an actual scene where light passes through a projection lens.
[0024] Figure 7 The projection lens uses a motor to focus and image the MTF diagram at 200mm to display the chip's MTF pattern.
[0025] Figure 8 The MTF diagram of the chip is displayed at 200mm by focusing the projection lens through the flat glass.
[0026] Figure 9 The projection lens uses a motor to focus and image the chip's MTF diagram at a distance of 600mm.
[0027] Figure 10 The MTF diagram of the chip is displayed at 600mm by focusing the projection lens through the flat glass.
[0028] Numbering on the map:
[0029] 100-Projection lens, 101-DMD chip, 102-Protective glass, 103-Prism equivalent plate, 110-First lens assembly, 111-First plate glass, 112-First spherical positive power lens, 113-Second spherical positive power lens, 114-Third spherical positive power lens, 115-Fourth spherical negative power lens, 116-Fifth spherical positive power lens, 117-Second plate glass, 118-Aperture stop, 120-Second lens assembly, 121-Sixth spherical positive power lens, 122-Seventh spherical negative power lens, 123-Eighth spherical negative power lens, 124-Ninth spherical positive power lens. Detailed Implementation
[0030] To make the technical problems, technical solutions, and beneficial effects to be solved by this application clearer, the following detailed description is provided in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and are not intended to limit the scope of this application.
[0031] It should be noted that when a component is referred to as being "fixed to" or "set on" another component, it can be directly on or indirectly on that other component. When a component is referred to as being "connected to" another component, it can be directly connected to or indirectly connected to that other component.
[0032] It should be understood that the terms "length", "width", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this application.
[0033] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this application, "multiple" means two or more, unless otherwise explicitly specified.
[0034] In the field of machine vision, the distance of the observed objects varies. The projection lens needs to be moved along the entire axis or along the axis of some components to achieve focus, so that objects at different working distances can be clearly imaged at the DMD (Digital Light Processing).
[0035] In certain scenarios, only a fixed, specific distance needs to be clearly imaged. Under normal circumstances, motor-driven focusing requires moving beyond the point of sharpest focus and then backtracking. This process introduces a backlash error, which needs compensation, and the resulting focus inconsistency affects the focusing effect. Confirming the optimal focus position requires additional camera shots and algorithmic capture, increasing the difficulty. Motor-driven focusing suffers from mechanical backlash error, focus recognition lag, and slow stepping response.
[0036] To achieve focusing by adjusting the lens without using a motor, embodiments of this application provide a projection lens 100, see reference. Figure 1-10 As shown, the projection lens includes a chip; a first component and a second component are arranged sequentially along the light emission direction of the chip; the second component includes a second lens assembly 120; the first component includes a first flat glass 111, a first lens assembly 110 and a second flat glass 117 arranged sequentially along the light emission direction of the chip; at least one of the first flat glass 111 and the second flat glass 117 is used to be extracted from the first component to achieve focus displacement of the projection lens.
[0037] The projection lens achieves focusing by inserting or removing the flat glass in different air gaps, thus changing the equivalent distance within the same air space and achieving axial movement of the lens assembly. See the optical path diagram for removing the first flat glass 111 or the second flat glass 117. Figure 4 and Figure 5 As shown.
[0038] Therefore, replacing motor focusing with inserting and withdrawing flat glass can avoid the disadvantages of poor return path, insensitive focus point recognition, and slow focusing speed.
[0039] Therefore, this embodiment of the application, by setting a first flat glass, a first lens assembly, and a second flat glass in the first component of the projection lens, and designing a structure in which at least one flat glass can be extracted from the first component, changes the optical path in the optical path by extracting the flat glass, thereby achieving focus displacement of the projection lens. Thus, this embodiment of the application can achieve focusing by adjusting the lens without using a motor. This embodiment of the application replaces the traditional motor-driven method, eliminating the need for a motor and related drive and transmission structures, thereby solving the problems of complex structure, high cost, easy wear and tear, and high power consumption caused by the use of motors in traditional technologies.
[0040] See Figure 1As shown, the chip is a DMD chip 101; the DMD chip, namely a Digital Micromirror Device (DMD), has a protective glass 102 and a prism equivalent plate 103 arranged sequentially in the light-emitting direction. The light-incoming side of the DMD chip is the side where light shines on the micromirror array, and the light-emitting side, that is, the side where light is output after being reflected by the micromirrors.
[0041] See Figure 2 As shown, the first flat glass 111 and the second flat glass 117 are located on both sides of the outermost end of the first lens assembly 110. Changing the optical path by inserting / removing the first flat glass 111 and the second flat glass 117 is equivalent to adjusting the air gap of the first lens assembly 110, thus achieving focal point shift (see...). Figure 4 and Figure 5 (As shown). See the actual scene of light passing through the projection lens. Figure 6 As shown.
[0042] See Figure 2 As shown, the first component also includes an aperture 118; the aperture is located on the rear side of the second flat glass 117 along the light emission direction of the chip.
[0043] Specifically, see Figure 2 As shown, the first component includes a first flat glass 111, a first spherical positive power lens 112, a second spherical positive power lens 113, a third spherical positive power lens 114, a fourth spherical negative power lens 115, a fifth spherical positive power lens 116, a second flat glass 117, and an aperture stop 118, wherein the fourth spherical negative power lens 115 and the fifth spherical positive power lens 116 are cemented together.
[0044] Furthermore, the first lens assembly includes a first spherical positive power lens 112, a second spherical positive power lens 113, a third spherical positive power lens 114, a fourth spherical negative power lens 115, and a fifth spherical positive power lens 116 arranged sequentially along the light emission direction of the chip.
[0045] Optionally, the first spherical positive power lens 112, the second spherical positive power lens 113, and the third spherical positive power lens 114 bear optical power through lens splitting to obtain a converged real image on the DMD chip 101.
[0046] Optionally, the first spherical positive power lens 112 is a positive meniscus lens, the second spherical positive power lens 113 is a biconvex lens, and the third spherical positive power lens 114 is a plano-convex lens.
[0047] See Figure 2As shown, the plane on the right side of the third spherical positive power lens 114 contacts the edge of the concave surface on the left side of the fourth spherical negative power lens 115; the convex surface on the left side of the third spherical positive power lens 114 is close to the convex surface on the right side of the second spherical positive power lens 113; the convex surface of the first spherical positive power lens 112 is close to the convex surface on the left side of the second spherical positive power lens 113.
[0048] The convex surfaces of the first spherical positive power lens 112 and the third spherical positive power lens 114 have opposite curvature directions. The second spherical positive power lens 113 is a biconvex lens. The curvature directions of the convex surfaces of the three lenses are coordinated to allow the light beam to pass through smoothly. By sharing the light deflection angle, the deflection angle of the light at the refraction surface is reduced, thereby reducing the generation of aberrations.
[0049] Optionally, the fourth spherical negative power lens is a biconcave lens; the fifth spherical positive power lens is a plano-convex lens; the concave surface on the right side of the fourth spherical negative power lens 115 and the convex surface on the left side of the fifth spherical positive power lens 116 are bonded together; the refractive index of the fourth spherical negative power lens is greater than or equal to 1.7, and the Abbe number is less than or equal to 30; the refractive index of the fifth spherical positive power lens is less than or equal to 1.65, and the Abbe number is greater than or equal to 60.
[0050] Optionally, the fourth spherical negative power lens 115 and the fifth spherical positive power lens 116 are cemented together. The cemented lens formed by the combination of the fourth spherical negative power lens 115 and the fifth spherical positive power lens 116 can correct coma and astigmatism through its biconcave profile and the cemented surface bent towards the aperture stop.
[0051] The fourth spherical negative power lens 115 and the fifth spherical positive power lens 116 of the first lens assembly form a cemented lens. Chromatic aberration correction is achieved through the cemented lens. The curvature of the cemented lens is used to correct coma and astigmatism. By using lens splitting to share the large power, spherical aberration is reduced and telecentricity is maintained.
[0052] To better correct chromatic aberration, preferably, the fourth spherical negative power lens 115 in the cemented lens is made of a material with high refractive index (Nd≥1.7) and low Abbe number (Vd≤30), and the fifth spherical positive power lens 116 is made of a material with low refractive index (Nd≤1.65) and high Abbe number (Vd≥60).
[0053] See Figure 3 As shown, the second lens assembly includes a sixth spherical positive power lens 121, a seventh spherical negative power lens 122, an eighth spherical negative power lens 123, and a ninth spherical positive power lens 124 arranged sequentially along the light emission direction of the chip.
[0054] The second lens assembly adopts a "positive-negative-negative-positive" arrangement in terms of optical power. It uses the height difference of the beam between the positive and negative lenses to correct the field curvature. The distortion is mainly corrected by the aberration correction unit formed by the "negative-positive" optical power combination at the outermost end of the lens.
[0055] Optionally, the seventh spherical negative power lens is a biconcave lens, and the eighth spherical negative power lens is a negative meniscus lens; the edges of the concave surfaces on the right side of the seventh spherical negative power lens 122 and the left side of the eighth spherical negative power lens 123 are in contact.
[0056] The seventh spherical negative power lens 122 and the eighth spherical negative power lens 123 form a negative power lens group, creating a larger air gap with the sixth spherical positive power lens 121. This allows the beam to achieve different heights in scenes where positive and negative power are separated, thereby correcting field curvature. The ninth spherical positive power lens 124 converges the beam, reducing the beam aperture entering the second lens assembly 120 and lowering aperture aberration. Simultaneously, the positive and negative power combination of the ninth spherical positive power lens 124 and the eighth spherical negative power lens 123 helps reduce distortion by balancing higher-order aberrations.
[0057] Optionally, the sixth spherical positive power lens is a biconvex lens; the ninth spherical positive power lens 124 is a plano-convex lens; the left side plane of the ninth spherical positive power lens 124 is close to the right side convex surface of the eighth spherical negative power lens 123. In this embodiment, "close" can refer to the small distance between two objects that are close to each other, meaning they may be in contact or not.
[0058] For example, the following is a comparison of the effects of a projection lens that uses a motor for focusing (replacing the flat glass in the projection lens with a motor assembly) and a projection lens that uses a retractable flat glass for focusing.
[0059] Experimental Background
[0060] To address the mechanical backlash and focus inconsistency issues in motor-driven focusing, and to verify the stability of the flat glass focusing solution, a comparative experiment was conducted.
[0061] Experimental methods
[0062] 1. Test conditions
[0063] The same projection lens is used (structural parameters are shown in Table 1).
[0064] Test object distance: 200mm (near distance), 600mm (medium distance) D
[0065] Evaluation metric: MTF (Modulation Transfer Function) value at a spatial frequency of 93 lp / mm.
[0066] 2. Focusing Operation
[0067] Motor focusing group: Axially moves the lens assembly to the position of sharp image (see...) Figure 7 , Figure 9 (As shown).
[0068] Flat glass focusing assembly: Extract the first flat glass (S10) or the second flat glass (S21) from the first assembly and fix it in place (see reference). Figure 8 , Figure 10 (As shown).
[0069] 3. Data Collection
[0070] The MTF curve is measured at the display chip (image plane) using optical testing equipment.
[0071] Compare the overlap of the MTF curves of the two schemes across the entire field of view at the same object distance. Figures 7-10 ).
[0072] Experimental results
[0073] Flat glass focusing group ( Figure 8 , Figure 10 The overlap of the MTF curves with the motor focusing group ( Figure 7 , Figure 9 Consistent.
[0074] See Figures 7-10 As shown, the OTF modulus represents the modulation transfer function (MTF), which describes the optical system's ability to transfer contrast across spatial frequency components. The observed line pair is 93 lp / mm. The MTF plot represents the overall resolving power of the optical system. The horizontal axis represents spatial frequency, in cycles per millimeter (cycles / mm), and the vertical axis represents the MTF value. The MTF value is used to evaluate the lens's image quality, ranging from 0 to 1. A higher and straighter MTF curve indicates better image quality, stronger ability to reproduce the true image, better overlap of curves across different fields of view, and better image quality consistency.
[0075] from Figures 7-8 It can be seen that in the visible light band, when the spatial frequency is 93 lp / mm, the MTF of the entire field of view is ≥0.45, indicating good image quality.
[0076] In the Ansys Zemax software, the parameters of each component in the projection lens of the above embodiment are shown in Table 1 below.
[0077] Table 1
[0078] surface type Radius of curvature (mm) Thickness (mm) Glass type Corresponding lens surface spherical unlimited 200 S1 spherical 34.07692 4 H-ZPK1A Ninth Spherical Positive Power Lens S2 spherical unlimited 0.2 S3 spherical 22.76483 1.8 H-ZPK1A Eighth spherical negative power lens S4 spherical 10.3779 3.827873 S5 spherical -48.8457 1.5 H-ZF2 Seventh spherical negative power lens S6 spherical 11.96772 5.454601 S7 spherical 25.51504 3.5 H-ZF52GT Sixth spherical positive power lens S8 spherical -44.49631 5.171746 Aperture spherical unlimited 3.247349 Aperture S10 spherical unlimited 0.6 B270 Second flat glass S11 spherical unlimited 2 S12 spherical -121.2055 3.5 H-ZPK1A Fifth spherical positive power lens S13 spherical -9.272582 1.5 H-ZF4A Fourth spherical negative power lens S14 spherical 78.17807 0.85 S15 spherical -72.73498 3.5 H-LAK53B Third spherical positive focal length lens S16 spherical -17.72051 0.2 S17 spherical 65.46335 3.8 H-ZPK1A Second spherical positive focal length lens S18 spherical -41.31619 0.2 S19 spherical 28.26833 3.5 H-LAK53B First spherical positive power lens S20 spherical 54.95316 2.302 S21 spherical unlimited 0.6 B270 First flat glass S22 spherical unlimited 5 S23 spherical unlimited 14 H-LAK7A Prism equivalent plate S24 spherical unlimited 0.6 S25 spherical unlimited 1.1 EAGLEXG Protective glass S26 spherical unlimited 0.303 Image spherical unlimited DMD chip
[0079] contrast Figure 7 and Figure 8, Figure 9 and 10 It can be seen that the MTF curve consistency of focusing the above projection lens by removing the flat glass is better than that of motor focusing, proving that its focusing stability is higher.
[0080] Therefore, the projection lens of this application embodiment changes the optical path by removing the flat glass, thereby realizing the focus displacement of the projection lens. Thus, this application embodiment can achieve focusing by adjusting the lens without using a motor. The first component and the second component achieve aberration correction through a reasonable combination of optical power.
[0081] The first component distributes optical power through lens splitting, reducing spherical aberration, coma, and astigmatism, which are mainly caused by aperture aberration. The cemented lens in the rear group can handle chromatic aberration correction for the entire lens. The front group of the lens achieves positive and negative distortion cancellation and field curvature correction through a combination of positive and negative optical power lenses, resulting in good overall image quality and mass production capability.
[0082] The first component uses a floating focus mechanism via a flat glass panel, a conventional approach suitable for close-range, wide-focusing scenarios. The large focus range, especially at close range, allows for significant changes in the lens's back focal length to compensate for aberrations caused by variations in the beam cone angle at different working distances. Adding flat glass panels at both ends of the first lens assembly near the display chip, similar to a rear-group floating focus mechanism, theoretically reduces design complexity.
[0083] The embodiments of this application employ flat glass focusing, which offers stable focusing performance and cost-effectiveness. Since the thickness and material of the flat glass are fixed, the introduced optical path difference is stable, making it more reliable than dynamic focusing methods using motors.
[0084] Secondly, this application provides a projection device, including the aforementioned projection lens.
[0085] The functions and effects of the technical features in this technical solution that are similar to or related to the aforementioned technical solution are similar to those in the aforementioned technical solution, and the inventive concept and beneficial effects of this technical solution are similar to those in the aforementioned technical solution, so they will not be repeated here.
[0086] The above are merely preferred embodiments of this application and are not intended to limit this application. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this application should be included within the protection scope of this application.
Claims
1. A projection lens characterized in that, It includes a light-emitting chip; a first component and a second component are sequentially arranged along the light-emitting direction of the light-emitting chip; the second component includes a second lens component; the first component includes a first flat glass, a first lens component and a second flat glass, sequentially arranged along the light-emitting direction of the light-emitting chip; At least one of the first flat glass and the second flat glass is used to be extracted from the first component to achieve focus shift of the projection lens.
2. The projection lens according to claim 1, characterized in that The light-emitting chip is a digital micromirror device; the light-emitting direction of the digital micromirror device is provided with a protective glass and a prism equivalent plate in sequence.
3. The projection lens according to claim 1 or 2, characterized in that The first component further includes an aperture; the aperture is disposed on the rear side of the second flat glass along the light emission direction of the light-emitting chip.
4. The projection lens according to claim 3, wherein, The first lens assembly includes a first spherical positive power lens, a second spherical positive power lens, a third spherical positive power lens, a fourth spherical negative power lens, and a fifth spherical positive power lens arranged sequentially along the light emission direction of the light-emitting chip.
5. The projection lens according to claim 4, wherein, The second lens assembly includes a sixth spherical positive power lens, a seventh spherical negative power lens, an eighth spherical negative power lens, and a ninth spherical positive power lens arranged sequentially along the light emission direction of the light-emitting chip.
6. The projection lens according to claim 5, wherein, The seventh spherical negative power lens is a biconcave lens, and the eighth spherical negative power lens is a negative meniscus lens; the edges of the concave surfaces of the seventh and eighth spherical negative power lenses are in contact.
7. The projection lens according to claim 6, wherein, The fourth spherical negative power lens is a biconcave lens; the fifth spherical positive power lens is a plano-convex lens; one concave surface of the fourth spherical negative power lens and the convex surface of the fifth spherical positive power lens are bonded together; the refractive index of the fourth spherical negative power lens is greater than or equal to 1.7, and the Abbe number is less than or equal to 30; the refractive index of the fifth spherical positive power lens is less than or equal to 1.65, and the Abbe number is greater than or equal to 60.
8. The projection lens according to claim 7, wherein, The first spherical positive power lens is a positive meniscus lens, the second spherical positive power lens is a biconvex lens, and the third spherical positive power lens is a plano-convex lens; the plane of the third spherical positive power lens is in contact with the edge of the other concave surface of the fourth spherical negative power lens; the convex surface of the third spherical positive power lens is close to one of the convex surfaces of the second spherical positive power lens; the convex surface of the first spherical positive power lens is close to the other convex surface of the second spherical positive power lens.
9. The projection lens of claim 5, wherein, The sixth spherical positive power lens is a biconvex lens; the ninth spherical positive power lens is a plano-convex lens; the plane of the ninth spherical positive power lens is close to the convex surface of the eighth spherical negative power lens.
10. A projection apparatus, characterized by, Includes the projection lens as described in any one of claims 1-9.