Conjugated lens and lens unit

Abstract

To reduce deterioration of optical characteristics caused by an adhesive in a conjugated lens.SOLUTION: When a volume of an internal space of an adhesive reservoir L50A is large and a volume of an adhesive stored therein is large, an adhesive layer G in a lens region Z1 is affected by volume change (shrinkage) as the adhesive hardens. Further, when a large amount of adhesive is stored in the adhesive reservoir L50A, this may have adverse optical effects on the lens unit. The sum of the volumes of the adhesive reservoir L50A and a communication part L50B is preferably considered based on a volume of an inter-lens surface space V0. When the volume of the inter-lens surface space V0 is α and the sum of the volumes of the adhesive reservoir L50A and the communication part L50B is β, an optimal range for β / α is preferably approximately 0.5≤β / α≤4.0.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] The present invention relates to a cemented lens formed by cementing a plurality of lenses together with an adhesive, and to a lens unit using the cemented lens. [Background technology]

[0002] For example, optical systems used in imaging devices mounted on automobiles, surveillance cameras, etc., use lens units with multiple lenses arranged along the optical axis (optical axis of the imaging device) from the object side to the image side (image sensor side). These lens units are designed to form a good image of an object using visible light on the image sensor. For this reason, it is required that the positional relationships between the lenses, between each lens and the lens barrel, and between the lens unit and the image sensor be fixed with high precision, and that no large load is applied to each lens.

[0003] Generally, lens barrels are made of resin, while lenses are made of two types of materials: resin and glass. The former has low mechanical strength but is inexpensive, while the latter has high mechanical strength but is expensive. Furthermore, for example, when the lens is aspherical, the former is less expensive than the latter. Furthermore, since the latter has a smaller thermal expansion coefficient, the latter is preferable for lenses in which thermal expansion has a particularly adverse optical effect. Furthermore, from the viewpoint of preventing distortion of the lens or lens barrel or deterioration of the positional accuracy of the lens relative to the lens barrel due to temperature changes, it is preferable for the thermal expansion coefficient of the lens barrel to be close to that of the lens, making lenses made of resin. Taking these points into consideration, it is decided which of the multiple lenses should be made of glass and which should be made of resin.

[0004] Among these, lenses made of resin materials (plastic lenses) are particularly press-fitted into a lens barrel also made of resin materials and fixed thereto. One form of such plastic lenses is a cemented lens as described in Patent Document 1. A cemented lens is formed by cementing two plastic lenses together with an adhesive, and the opposing lens surfaces of these lenses have a common shape. Such cemented lenses are particularly effective in correcting chromatic aberration with a small number of lenses.

[0005] However, when two lenses are bonded together with an adhesive in this way, air bubbles may become trapped in the adhesive between the lens surfaces. Patent Document 1 describes a method for suppressing the formation of such bubbles by making the adhesive layer (the gap between the opposing lens surfaces) thinner on the central axis side and thicker on the peripheral side, and by providing an adhesive reservoir to store excess adhesive between the lenses on the outer side of the lens surfaces. If an insufficient amount of adhesive is supplied, a gap without adhesive may be formed between the lens surfaces. Therefore, by providing such an adhesive reservoir and making the amount of adhesive supplied during bonding greater than the volume of the space between the lens surfaces, excess adhesive can be stored in the adhesive reservoir. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Publication No. 2023-118925 Summary of the Invention [Problem to be solved by the invention]

[0007] Problems caused by the adhesive occurred even when cemented lenses were manufactured using the technology described in Patent Document 1. First, in this case, excess adhesive that could not be contained even in the adhesive reservoir could adversely affect the positional relationship between the two lenses in the cemented lens.

[0008] From this perspective, it is effective to increase the volume of the adhesive reservoir to prevent such excess adhesive from occurring. However, if the volume of adhesive in the adhesive reservoir increases, the adhesive layer between the lens surfaces may be sucked up into the adhesive reservoir during solidification due to a change in volume (shrinkage) of the adhesive, forming voids in the adhesive layer between the lens surfaces. Furthermore, in this case, the adhesive reservoir is located outside the lens surfaces and is not in the optical path, but stray light from the adhesive in the adhesive reservoir may enter the optical path and cause ghosts.

[0009] For this reason, there has been a demand for a cemented lens in which deterioration of optical characteristics caused by adhesives is reduced, or a lens unit using such a cemented lens.

[0010] The present invention has been made in view of the above circumstances, and has an object to provide a lens unit that reduces the deterioration of optical characteristics caused by the adhesive in the cemented lens and has good imaging characteristics. [Means for solving the problem]

[0011] The cemented lens according to the present invention is a cemented lens having a configuration in which a first lens surface, which is one lens surface of a first lens, and a second lens surface, which is one lens surface of a second lens, are opposed to each other and cemented together with an adhesive along an optical axis, wherein a distance between the first lens surface and the second lens surface along a normal direction of the first lens surface and the second lens surface is constant, and an internal space is ensured by a lens surface inter-surface space where the first lens surface and the second lens surface are opposed to each other and spaced apart, and by a lens region where the lens surface inter-surface space is formed, the distance between the first lens and the second lens being locally wider on the radial direction outer side as viewed from the optical axis, and the optical axis is The lens assembly includes an adhesive reservoir formed to surround the lens area when viewed from the axis, and a communicating portion that connects the adhesive reservoir to the space between the lens surfaces between the first lens and the second lens, and a first positioning surface that faces the second lens on the first lens and a second positioning surface that faces the first lens on the second lens abut on the radially outer side of the adhesive reservoir, and where α is the volume of the space between the lens surfaces and β is the sum of the volume of the adhesive reservoir and the volume of the communicating portion, 0.5≦β / α≦4.0, and the first lens and the second lens are joined together with the space between the lens surfaces and the communicating portion filled with the adhesive. In this configuration, by appropriately setting the range of β / α, it becomes easier to supply a sufficient amount of adhesive to the space between the lens surfaces, which is the most important part of a cemented lens, and also reduces the adverse optical effects of the adhesive in the adhesive reservoir, making it possible to easily manufacture cemented lenses with excellent optical properties.

[0012] In this case, α≦β may be satisfied. This makes it possible to obtain a cemented lens with good optical characteristics, and also allows for a greater tolerance in setting the amount of adhesive used during cementing, making it particularly easy to manufacture cemented lenses. The first lens surface may be concave, the second lens surface may be convex, the lens surface of the first lens opposite to the first lens surface may be concave, and the lens surface of the second lens opposite to the second lens surface may be convex, and the radii of curvature of the first lens surface and the second lens surface may be 1.5 mm or less. When the refractive index of the resin material constituting the first lens is n1, the refractive index of the resin material constituting the second lens is n2, and the refractive index of the adhesive after solidification is n3, |n2-n3|<|n1-n3| may be satisfied. This arrangement of the first and second lenses is particularly effective in reducing various aberrations when the cemented lens is located closest to the image side of the lens unit, making it possible to obtain a lens unit with excellent imaging characteristics.

[0013] The lens unit of the present invention is a lens unit having a configuration in which a plurality of lenses are fixed inside a cylindrical lens barrel from the object side to the image side in a direction along an optical axis, and the cemented lens is used as the lens located closest to the image side among the plurality of lenses. In this lens unit, the cemented lens having the above-mentioned excellent optical characteristics is used, and therefore the imaging characteristics are excellent. The adhesive reservoir may be located further outward from the image-side opening of the lens barrel as viewed from the optical axis. In this lens unit, the influence of the adhesive in the adhesive reservoir on the imaging characteristics is reduced, and therefore the imaging characteristics are particularly excellent. [Effects of the Invention]

[0014] According to the present invention, it is possible to obtain a lens unit that reduces the deterioration of optical characteristics caused by the adhesive in the cemented lens and has good imaging characteristics. [Brief explanation of the drawings]

[0015] [Figure 1] FIG. 1 is a cross-sectional view taken along the optical axis of a lens unit in which a cemented lens according to an embodiment is used. [Figure 2] FIG. 1 is an exploded view of a lens unit using a cemented lens according to an embodiment. [Figure 3] 1A is a cross-sectional view taken along the optical axis of a cemented lens according to an embodiment, and FIG. 1B is an exploded view thereof. [Figure 4] FIG. 2 is an enlarged cross-sectional view of a cemented portion of the cemented lens according to the embodiment. [Figure 5] 5A to 5C are cross-sectional views showing steps in a method for manufacturing a cemented lens according to an embodiment. [Figure 6] 10 shows the results of judging whether the optical characteristics are good or bad when β / α is changed in a cemented lens provided with an adhesive reservoir. DETAILED DESCRIPTION OF THE INVENTION

[0016] Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings. Fig. 1 is a cross-sectional view taken along an optical axis A of a lens unit 1 that uses a cemented lens L50 according to this embodiment. Fig. 2 is an exploded view of this lens unit 1.

[0017] In Fig. 1, the object (Ob) side is the upper side, the image (Im) side is the lower side, and the imaging element (not shown) is located at the bottom. Lenses L1 to L3, lens body L40 including lens L4, and cemented lens L50 formed by integrating lenses L5 and L6 are each fixed directly or indirectly to lens barrel 10. Fig. 1 mainly shows the individual lenses and the related configuration, and although a structure for fixing the positional relationship between the imaging element and lens barrel 10 is actually provided, this is not shown.

[0018] The imaging element is a two-dimensional CMOS image sensor, and the pixels are arranged two-dimensionally in a plane perpendicular to the optical axis A. In Fig. 1, lens unit 1 is configured in which lenses L1 through cemented lens L50 are fixed from the object side to the image side of lens barrel 10. Lens unit 1 is configured to form a visible light image of the object to be imaged on the imaging element (image plane) in a desired field of view and in a desired form.

[0019] 1 and 2, lens L1, which is located closest to the object (top in the figure), is a fisheye lens, and it mainly determines the field of view of the imaging device. An O-ring 30 is provided between lens L1 and lens barrel 10 to seal the gap between them. Lens L2, lens L3, lens body L40 (lens L4), and cemented lens L50 (lenses L5 and L6) are arranged in this order closer to the imaging element (Im side) than lens L1. Each lens has a shape that is approximately symmetrical about optical axis A, and in particular, the lens surface (the surface of the lens onto which light rays that contribute to image formation enter or exit) also has a shape that is symmetrical about optical axis A. A diaphragm 20 for limiting the light beam is provided between lens L3 and lens body L40, and a thin-film light-shielding plate 21 for removing unnecessary light is provided between lens L2 and lens L3.

[0020] In FIG. 1, the object-side and image-side lens surfaces of each lens are appropriately curved (convex or concave) so that the lens unit 1 provides the desired imaging characteristics. Furthermore, lens L1, located closest to the object, is located at the outermost surface of the imaging device and is therefore made of scratch-resistant glass. Furthermore, since the lenses adjacent to the aperture 20 (lenses L3 and L4) are subject to significant changes in focal length due to temperature changes, lens L4 is made of glass. The other lenses are made of inexpensive resin materials. However, lens L4 is actually housed and fixed in lens holder 41 made of resin material, forming lens body L40, which is fixed within lens barrel 10.

[0021] Crystalline plastics (polyethylene, polyamide, polytetrafluoroethylene) with excellent weather resistance are preferably used as the material for lens barrel 10. On the other hand, lenses L2, L3, L5, and L6 are made of amorphous plastics (polycarbonate, etc.) with excellent lens performance (light transmittance and moldability). Lenses L5 and L6 will be described in detail below.

[0022] 1, lenses L5 and L6 are cemented together, including their lens surfaces, with an adhesive to form cemented lens L50. Therefore, in practice, this cemented lens L50 can be handled as a plastic lens, similar to lens L3, etc., within lens barrel 10. This cemented lens L50 is a cemented lens according to an embodiment of the present invention.

[0023] In FIG. 1, the lenses, lens body L40, and cemented lens L50 use structures provided outside the optical path, such as on the outside of the lens surfaces, to fix the positional relationship between adjacent lenses (including lens body L40 and cemented lens L50) along the optical axis A and their positions relative to the lens barrel 10. This is similar to the technology described in, for example, Japanese Patent Application Laid-Open No. 2021-005019. In FIG. 1, cemented lens L50 is supported by cemented lens support surface 11, which is formed on the image side of the lens barrel 10 and perpendicular to the optical axis A, and is fixed to the lens barrel 10. In addition, an image-side opening 10A is formed at the most image side of the lens barrel 10, which emits light that has passed through cemented lens L50 toward the image side, and the image sensor is located closer to the image than this image-side opening 10A.

[0024] 1, the object-side lens surface of each lens is called the first surface R1, and the image-side lens surface is called the second surface R2. Furthermore, the shape of the lens surface (convex or concave) refers to the shape of the first surface R1 as seen from the object side, and the shape of the second surface R2 as seen from the image side.

[0025] The lens (first lens) L5 constituting the cemented lens L50 is a negative lens with its object-side lens surface L5R1 being a concave curved surface and its image-side lens surface L5R2 (first lens surface) being a concave curved surface. The lens (second lens) L6 constituting the cemented lens L50 is a positive lens with an outer diameter smaller than that of the lens L5 and with its object-side lens surface L6R1 (second lens surface) being a convex curved surface and its image-side lens surface L6R2 being a convex curved surface. Here, the lens surface (first lens surface) L5R2 and the lens surface (second lens surface) L6R1 have a common shape and are cemented together with a thin adhesive layer (not shown in FIGS. 1 and 2) to form the cemented lens L50.

[0026] If the lens closest to the image side is such a cemented lens L50, the lenses L5 and L6 that make it up can be made of different materials and their refractive indices can be adjusted individually, thereby reducing (adjusting) chromatic aberration in the lens unit 1.

[0027] 3A is a cross-sectional view of cemented lens L50 taken along optical axis A, and FIG. 3B is an exploded view thereof. As shown in FIG. 3A, in this cemented lens L50, an adhesive reservoir L50A, which is a space for storing excess adhesive, is provided as a cavity formed at the interface between lenses L5 and L6, outside lens surface L5R2 (L6R1) as viewed from optical axis A. Adhesive reservoir L50A is formed in a substantially annular shape centered on optical axis A. Here again, a description of the adhesive is omitted.

[0028] Furthermore, on the image side of lens L5, radially outward of adhesive reservoir L50A as viewed from the optical axis A, there is formed a lens positioning surface (first positioning surface) L5A consisting of a plane perpendicular to the optical axis A. Correspondingly, on the object side of lens L6, radially outward of adhesive reservoir L50A as viewed from the optical axis A, there is formed a lens positioning surface (second positioning surface) L6A consisting of a plane perpendicular to the optical axis A. Although a cross section is shown in Figure 3, lens positioning surface L5A and lens positioning surface L6A are both formed in an annular shape centered on the optical axis A.

[0029] As described above, the cemented lens L50 is supported by the cemented lens support surface 11 on the lens barrel 10, and the cemented lens fixing surface L5B formed radially outward of the lens positioning surface L5A on the lens L5 abuts against the cemented lens support surface 11 in FIG. 1. The outer peripheral surface L5C of the lens L5 as viewed from the optical axis A engages with the inner surface of the hole in the lens barrel 10 that houses the cemented lens L50 and other components, and is set to determine the positional relationship of the cemented lens L50 with respect to the lens barrel 10. This is similar to the technology described in, for example, JP 2021-005019 A, as described above, and is unrelated to the present invention, so a detailed explanation will be omitted. The following description will focus only on matters relating to the interface between the lenses L5 and L6. The structure for determining the positional relationship between adjacent lenses, etc. (including lens body L40 and cemented lens L50) and between each lens, etc. and the lens barrel 10 is the same as the technology described in Patent Publication No. 2021-005019, etc., for each lens and lens body L40.

[0030] Figure 4 is an enlarged cross-sectional view of region X in Figure 3(a) (the joint between lens L5 and lens L6 on the left side of optical axis A in the figure). For the sake of explanation, the dimensions of each part are exaggerated compared to their actual size. The adhesive layer G between lens L5 and lens L6 is also shown here.

[0031] In this cemented lens L50, a lens region Z1, a communicating region Z2, and a positioning region Z3 are provided at the interface between these lenses in this order from the side closest to the optical axis A (the right side in Figure 4), and an adhesive reservoir L50A is provided between the communicating region Z2 and the positioning region Z3.

[0032] Lens region Z1 is a region where a space V0 is formed between lens surfaces L5R2 and L6R1, where the lens surfaces L5R2 and L6R1 face each other via a thin adhesive layer G. Here, the thickness of the adhesive layer G (or the space V0 between the lens surfaces) along the normal to the curved surfaces that define the shapes of the lens surfaces L5R2 and L6R1 is constant, unlike the technology described in Patent Document 1. This thickness is, for example, 13 μm ± 3 μm. This thickness is negligibly small compared to the radius of curvature of the lens surfaces, and approximately, the curved shapes of the lens surfaces L5R2 and L6R1 can be made the same. Lens region Z1 is the region that forms the optical path during imaging and is the region that primarily functions optically in this cemented lens L50. For this reason, the positional relationship between the lens surfaces L5R2 and L6R1 in lens region Z1 must be set with high precision. Furthermore, the presence of air bubbles or voids in the adhesive layer G between the lens surfaces L5R2 and L6R1 can cause flare and other degradation in image quality, so these must be absent.

[0033] Outside the lens region Z1 as viewed from the optical axis A (on the left side in FIG. 4) and inside the adhesive reservoir L50A, there is provided a communication portion L50B, which is a hollow portion formed by the opposing and spaced-apart image-side surface of the lens L5 (the lower side in the figure) and communicates with the inter-lens surface space V0 and the adhesive reservoir L50A. When manufacturing this cemented lens L50, the adhesive before solidification flows from the lens region Z1 (the inter-lens surface space V0) through the communication region Z2 (communicating portion L50B) into the adhesive reservoir L50A.

[0034] In the lens region Z1, the communication region Z2, and the adhesive reservoir L50A, the image-side surface of lens L5 and the object-side surface of lens L6 are closely opposed to each other and do not abut, as described above. In contrast, in the outermost positioning region Z3, the lens positioning surface (first positioning surface) L5A on the lens L5 side and the lens positioning surface (second positioning surface) L6A on the lens L6 side directly abut each other. This determines the positional relationship between lenses L5 and L6 in the direction along the optical axis A of the cemented lens L50. Therefore, the adhesive does not flow into the positioning region Z3 before solidification, and an adhesive layer G is not formed.

[0035] Although the lens positioning surfaces L5A and L6A are formed to have an annular shape as described above, their planar shapes (shapes viewed from the direction of the optical axis A) can be set as appropriate, at least as long as the positional relationship of the lenses L5 and L6 in the direction along the optical axis A can be determined using these surfaces. For example, they do not need to be formed continuously in the circumferential direction.

[0036] FIG. 5 is a cross-sectional view showing the steps in manufacturing this cemented lens L50 (cementing lenses L5 and L6). The upside-down relationship is reversed compared to FIGS. 1, 3, and 4. As shown in FIG. 5(a), unsolidified adhesive G0 is dispensed onto lens surface L5R2 of lens L5, which has a concave shape. Then, as shown in FIG. 5(b), lens L6 is attached onto the concave surface. Finally, as shown in FIG. 5(c) (FIG. 4), the lens positioning surface L5A on the lens L5 side and the lens positioning surface L6A on the lens L6 side are brought into direct contact with each other in positioning region Z3. In this state, the unsolidified adhesive spreads from the center outward.

[0037] As described above, the adhesive layer G must be formed without any air bubbles or voids in the lens region Z1. To form the adhesive layer G without any voids in the lens region Z1, the amount of adhesive G0 before solidification in FIG. 5(a) must be greater than the volume of the space V0 between the lens surfaces. In this case, the excess adhesive passes through the communicating portion L50B (communicating region Z2) and reaches the adhesive reservoir L50A.

[0038] On the other hand, as mentioned above, it is preferable that the adhesive not flow between the lens positioning surfaces L5A and L6A in the positioning region Z3. For this reason, it is preferable that the excess adhesive described above remain in the adhesive reservoir L50A. From this perspective, it is preferable that the volume of the internal space of the adhesive reservoir L50A, or more precisely, the sum of the volume of this and the volume of the internal space of the communication region Z2, is large.

[0039] However, the inventors have found that when the volume of the internal space of adhesive reservoir L50A is large and the volume of adhesive contained therein is large, the adhesive layer G in lens region Z1 is affected by volume changes (shrinkage) that accompany the hardening of the adhesive. That is, when the volume of adhesive contained in adhesive reservoir L50A is large in this way, the adhesive present in the inter-lens surface space V0 before solidification is sucked up into adhesive reservoir L50A, which can cause voids in the adhesive layer G in the inter-lens surface space V0. These voids are larger than the air bubbles identified as the problem to be solved in Patent Document 1, and cause flare and ghosting in the lens unit 1 of FIG. 1.

[0040] Furthermore, if the amount of adhesive G0 contained in the adhesive reservoir L50A is large, this may have an adverse optical effect on the lens unit 1 of FIG. 1. As mentioned above, the adhesive reservoir L50A is not located on the original optical path of the lens unit 1. However, if the refractive index of the solidified adhesive G0 differs from the refractive index of the resin material that makes up the lenses L5 and L6, reflections may occur at the interfaces between the adhesive layer G (solidified adhesive) in the adhesive reservoir L50A and the lenses L5 and L6, and stray light may be reflected there and mixed into the original optical path. Such stray light may cause ghosting in the lens unit 1 of FIG. 1.

[0041] Conversely, if the volume of adhesive reservoir L50A is small, excess adhesive may reach positioning region Z3, as described above, deteriorating the positional relationship between lens L5 and lens L6. Alternatively, to prevent this situation from occurring, it is essential to set the amount of adhesive G0 dispensed before solidification in Figure 5(a) to a small amount. In this case, the amount of adhesive G0 remaining in lens region Z1 may be insufficient, potentially forming voids in the adhesive layer G. For this reason, there is an appropriate range for the sum of the volumes of adhesive reservoir L50A and communication portion L50B.

[0042] It is preferable to consider the sum of the volumes of the adhesive reservoir L50A and the communication portion L50B with reference to the volume of the space V0 between the lens surfaces. That is, when the volume of the space V0 between the lens surfaces is α and the sum of the volumes of the adhesive reservoir L50A and the communication portion L50B is β, there is an appropriate range for the ratio of α to β. In this case, the input amount (volume) VG of the adhesive G0 dropped in the state of FIG. 5(a) needs to be in the range of α < VG < α + β in order not to let the adhesive flow out to the outside from the adhesive reservoir L50A while filling the space V0 between the lens surfaces. However, even within this range, the above-mentioned problems may occur.

[0043] Here, in Patent Document 1, the thickness of the adhesive layer G in the lens region Z1 is made thinner on the optical axis side and thicker on the outside. That is, in this case, the shapes of the first lens surface of the first lens and the second lens surface of the second lens in the above configuration are set in this way.

[0044] However, in this case, similar to the case of the adhesive reservoir L50A described above, stray light reflection at the interface between each of these lens surfaces and the adhesive layer G was likely to occur. In particular, in this case, since a thick region of the adhesive layer G is provided in the space V0 between the lens surfaces, this situation became prominent.

[0045] Therefore, in the following embodiments, particularly in the space V0 between the lens surfaces, it is assumed that the thickness of the adhesive layer G is constant. This thickness is the thickness along the normal direction of the lens surface in this region. In the following embodiments, this thickness T0 is set to 13 μm. In the actual lens unit 1, the radii of curvature of the lens surface L5R2 of the lens L5 and the lens surface L6R1 of the lens L6 are 1.5 mm or less, and the object-side and image-side surfaces of the lens L5 are concave shapes, and the object-side and image-side surfaces of the lens L6 are convex shapes. Such a configuration is particularly effective in correcting various aberrations such as chromatic aberration by the cemented lens L50 in the lens unit 1 of FIG. 1.

[0046] For this reason, in the following examples, the radius of curvature of the lens surface L5R2 of the lens L5 and the lens surface L6R1 of the lens L6 was set to 1.491 mm, and the lens diameter (radius of the lens region Z1) was set to 1.238 mm. In this case, the state of the cemented lens L50 and the imaging state of the lens unit 1 using this cemented lens were examined when the volume of the adhesive reservoir L50A was changed. Here, β / α was set to 0.1 to 30.0. Here, the volume of the communication portion L50B was kept constant, and the amount of adhesive G0 dispensed in Figure 5(a) was set to an amount such that the adhesive G0 before solidification reached the adhesive reservoir L50A in the state shown in Figure 5(c) (a state in which the adhesive amount VG was small) and an amount such that the adhesive reservoir L50A was nearly filled (a state in which the adhesive amount VG was large). Figure 6 shows the results.

[0047] The results show that when β / α is smaller than 0.33 (when the volumes of the adhesive reservoir L50A and the communication portion L50B are small), the imaging characteristics of the lens unit 1 deteriorate. The cause of this deterioration was that when the amount of adhesive input was small, there were voids that occurred in the adhesive layer G in the space V0 between the lens surfaces, and when the amount of adhesive input was large, there was deterioration in the positional relationship between the lenses L5 and L6 (including tilt with respect to the optical axis A) due to adhesive G0 flowing into the positioning region Z3. In other words, the optical characteristics deteriorated both when the amount of adhesive input VG was small and when it was large.

[0048] Furthermore, when β / α was greater than 5.0 (when the volumes of the adhesive reservoir L50A and the communicating portion L50B were large), the imaging characteristics of the lens unit 1 also deteriorated. The cause of this deterioration was a void that appeared in the adhesive layer G in the space V0 between the lens surfaces due to a change in volume of the adhesive when it hardened when there was a large amount of adhesive stored in the adhesive reservoir L50A and the communicating portion L50B. Also, ghost images were generated due to reflections on the adhesive layer G (solidified adhesive) in the adhesive reservoir L50A and the inner surface of the adhesive reservoir L50A.

[0049] On the other hand, when β / α is in the range of 0.5 to 4.0, good optical characteristics were obtained. From this result, as an optimal range for β / α, about 0.5 ≤ β / α ≤ 4.0 is preferable. The amount of adhesive VG dropped in the state of Fig. 5(a) can improve the optical characteristics of the lens unit 1 using this bonding lens L50 by setting it in the range of α < VG < α + β in this case. However, particularly when β ≥ α (i.e., 1.0 ≤ β / α ≤ 4.0) within the above range, the manufacturing becomes particularly easy because the setting margin of the adhesive input amount VG becomes larger, and the deterioration of the optical characteristics as described above does not occur, so it is particularly preferable.

[0050] Also, in order to reduce the optical influence caused by the adhesive layer G in the adhesive reservoir L50A as described above, it is effective to provide the adhesive reservoir L50A at a location separated from the optical axis A. Particularly, in Fig. 1, by providing the adhesive reservoir L50A outside the image-side aperture 10A in the radial direction, this influence can be reduced.

[0051] Also, the reflection at the interface between the adhesive layer G and the lenses L5 and L6 may occur not only on the inner surface of the adhesive reservoir L50A but also in the lens region Z1 and the communication region Z2. Therefore, if a material with a refractive index as close as possible to the refractive index of the lens L5 and the refractive index of the lens L6 is selected as the adhesive, this reflection can be suppressed. Here, as described above, when the lenses L5 and L6 are made of materials with different refractive indices, the situation of this reflection is different between the lens L5 side and the lens L6 side.

[0052] In order to reduce chromatic aberration as described above, the refractive index (n1) of the lens L5 is made larger than the refractive index (n2) of the lens L6. Also, if the refractive index (n3) of the adhesive after curing is made smaller than the resin materials constituting the lenses L5 and L6, for example, 1.486 (< n1, n2), for example, when the refractive index (n1) of the lens L5 is 1.656 and the refractive index (n2) of the lens L6 is 1.544, |n2 - n3| < |n1 - n3|, and the reflection on the lens L6 side can be reduced.

[0053] That is, when the refractive index n1 of lens L5 and the refractive index n2 of lens L6 are changed, it is preferable to set n1 and n2 so as to reduce chromatic aberration and satisfy this condition. Furthermore, in order to reduce the influence of reflection at the interface as described above, it is particularly preferable to set n3 close to n1 and n2.

[0054] 1 and 3, lens L5 is biconcave and lens L6 is biconvex, so lens L6 is thicker than lens L5. When lens L6 is thick and convex with a curvature radius of 1.5 mm or less, even if minute recesses on the order of nanometers are formed on the surface during manufacturing, the effect of these recesses can be eliminated by making n3 close to n2. In other words, by setting the refractive index as described above, it is possible to reduce the degradation of optical characteristics in this case.

[0055] 1, the cemented lens L50 is used closest to the image, but cemented lenses can also be used in other locations. In this case, the above-described configuration is effective regardless of the location. Also, in the above example, both the adhesive reservoir L50A and the communication portion L50B are formed annularly (continuously in the circumferential direction) around the optical axis A, but they do not need to be formed continuously in the circumferential direction as long as they can accommodate the unsolidified adhesive from the lens region Z1 side.

[0056] (Main features of this form) The features of this embodiment can be briefly summarized as follows. (1) This cemented lens L50 has a configuration in which a first lens surface L5R2, which is one of the lens surfaces of lens L5, and a second lens surface L6R1, which is one of the lens surfaces of lens L6, are opposed to each other and cemented together with an adhesive G0 along the optical axis A, and the distance between the first lens surface L5R2 and the second lens surface L6R1 along the normal direction of the first lens surface L5R2 and the second lens surface L6R1 is constant, and an internal space is established by forming an inter-lens surface space V0 where the first lens surface L5R2 and the second lens surface L6R1 are spaced apart from each other, and by locally widening the distance between the lenses L5 and L6 radially outward from the optical axis A relative to a lens region Z1 where the inter-lens surface space V0 is formed. The lens L5 and lens L6 are provided with an adhesive reservoir L50A formed to surround the lens region Z1 when viewed from the optical axis A, and a communication portion L50B that connects the adhesive reservoir L50A to the space between the lens surfaces V0 between the lenses L5 and L6, and on the radial outside of the adhesive reservoir L50A, a first positioning surface L5A that faces the lens L6 side of the lens L5 and a second positioning surface L5B that faces the lens L5 side of the lens L6 abut against each other, and when the volume of the space between the lens surfaces V0 is α and the sum of the volume of the adhesive reservoir L50A and the volume of the communication portion L50B is β, the relationship is 0.5≦β / α≦4.0, and the lenses L5 and L6 are joined together with the space between the lens surfaces V0 and the communication portion L50B filled with adhesive G0. In this configuration, by appropriately setting the range of β / α, it becomes easier to supply a sufficient amount of adhesive G0 to the space V0 between the lens surfaces, which is the most important part of the cemented lens L50, and it also reduces any adverse optical effects caused by the adhesive G0 in the adhesive reservoir L50A, making it possible to easily manufacture a cemented lens L50 with good optical properties.

[0057] (2) Here, α≦β. This makes it possible to obtain a cemented lens L50 with good optical characteristics as described above, and also makes it possible to increase the tolerance for setting the amount VG of adhesive used during cementing, making it particularly easy to manufacture the cemented lens L50.

[0058] (3) The first lens surface L5R2 is concave, the second lens surface L6R1 is convex, the lens surface L5R1 on the opposite side of the first lens surface L5R2 on the lens L5 is concave, and the lens surface L6R2 on the opposite side of the second lens surface L6R1 on the lens L6 is convex, and the radii of curvature of the first lens surface L5R2 and the second lens surface L6R1 are 1.5 mm or less. (4) When the refractive index of the resin material constituting lens L5 is n1, the refractive index of the resin material constituting lens L6 is n2, and the refractive index of the adhesive G0 after solidification is n3, |n2-n3|<|n1-n3| is satisfied. Such a setting of lenses L5 and L6 is particularly effective in reducing various aberrations when cemented lens L50 is located closest to the image side in the lens unit, making it possible to obtain a lens unit with excellent imaging characteristics.

[0059] (5) In this lens unit 1, a plurality of lenses are fixed inside a cylindrical lens barrel 10 from the object (Ob) side to the image (Im) side in a direction along the optical axis A, and a cemented lens L50 is used as the lens located closest to the image side among the plurality of lenses. In this lens unit 1, the cemented lens L50 having the above-described favorable optical characteristics is used, and therefore the imaging characteristics are excellent. (6) The adhesive reservoir L50A is located on the outer side of the image-side opening 10A, which is the opening on the image (Im) side of the lens barrel 10, as viewed from the optical axis A. In this lens unit 1, the influence of the adhesive in the adhesive reservoir L50A on the imaging characteristics is reduced, and therefore the imaging characteristics are particularly excellent.

[0060] The present invention has been described based on an embodiment and its modifications, but this embodiment is merely an example, and it will be understood by those skilled in the art that various modifications are possible in terms of the combination of the respective components, and that such modifications are also within the scope of the present invention. [Explanation of symbols]

[0061] 1 Lens unit 10 Telescope tube 10A image side aperture 11 cemented lens support surface 20 apertures 21 Shade 30 O-rings 41 Lens holder A optical axis G Adhesive layer G0 adhesive Im image (side) L1~L4 lenses L5 lens (first lens) L5A Lens positioning surface (first positioning surface) L5B cemented lens fixing surface L5C outer surface L5R2 First lens surface L6 lens (second lens) L6A Lens positioning surface (second positioning surface) L6R1 Second lens surface L40 lens body L50 cemented lens L50A adhesive reservoir L50B communication part Ob object (side) R1 1st surface R2 2nd surface V0 Lens surface space Z1 lens range Z2 communication area Z3 positioning area

Claims

1. A cemented lens having a configuration in which a first lens surface, which is one lens surface of a first lens, and a second lens surface, which is one lens surface of a second lens, are bonded together with an adhesive along an optical axis in an opposing configuration, an inter-lens surface space in which the first lens surface and the second lens surface are opposed to each other with a gap therebetween, with a constant interval between the first lens surface and the second lens surface along a normal direction of the first lens surface and the second lens surface; an adhesive reservoir formed so as to surround the lens area as viewed from the optical axis, in which an internal space is secured by locally widening the interval between the first lens and the second lens at a radially outer side as viewed from the optical axis than the lens area in which the inter-lens surface space is formed; a communication portion that communicates the adhesive reservoir with the space between the lens surfaces between the first lens and the second lens; Equipped with a first positioning surface of the first lens facing the second lens and a second positioning surface of the second lens facing the first lens are in contact with each other at an outer side of the adhesive reservoir in the radial direction; where α is the volume of the space between the lens surfaces and β is the sum of the volume of the adhesive reservoir and the volume of the communication portion, 0.5≦β / α≦4.0; A cemented lens, wherein the first lens and the second lens are cemented together in a state in which the space between the lens surfaces and the communicating portion are filled with the adhesive.

2. 2. The cemented lens according to claim 1, wherein α≦β.

3. 3. The cemented lens according to claim 1, wherein the first lens surface is a concave surface, the second lens surface is a convex surface, a lens surface of the first lens opposite to the first lens surface is a concave surface, and a lens surface of the second lens opposite to the second lens surface is a convex surface, and radii of curvature of the first lens surface and the second lens surface are 1.5 mm or less.

4. The refractive index of the resin material constituting the first lens is n １ , the refractive index of the resin material constituting the second lens is n ２ and the refractive index of the adhesive after solidification is n ３ When |n ２ -n ３ |<|n １ -n ３ 3. The cemented lens according to claim 1, wherein:

5. A lens unit having a configuration in which a plurality of lenses are fixed inside a cylindrical lens barrel from the object side to the image side in a direction along an optical axis, 3. A lens unit, comprising: the cemented lens according to claim 1 or 2, as the lens positioned closest to the image side among the plurality of lenses.

6. 6. The lens unit according to claim 5, wherein the adhesive reservoir is located outside the image-side opening of the lens barrel as viewed from the optical axis.

Images