JP2006284656A - Light antireflection optical system and imaging optical system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a light antireflection optical system and an imaging optical system capable of greatly suppressing reflected light generated on the interface of a plane of an optical member and an adhesion layer provided on the plane with simple constitution. <P>SOLUTION: Multilayer antireflective films 21 and 22 are formed on the interface between a ghost prevention member 5 and the adhesion layer 23, and the interface between the adhesion layer 23 and a half-prism 2. Glass materials forming the ghost prevention member 5 and half-prism 2 are BK7 and the refractive index n<SB>1</SB>to its (d) line is 1.516; and an adhesive forming the adhesion layer 23 is epoxy resin and the refractive index n<SB>2</SB>to its (d) line is 1.56. The antireflective film 21 is a multilayer film of three-layered constitution formed by laminating an SiO<SB>2</SB>layer, an Al<SB>2</SB>O<SB>3</SB>layer, and an SiO<SB>2</SB>layer in order on the plane 13 of the ghost prevention member 5. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a light reflection preventing optical system and an imaging optical system applied to an optical system in which minute light reflection is a problem, and in particular, a ghost of a video camera or a digital camera using an imaging element having a relatively high surface reflectance. The present invention relates to a light reflection preventing optical system and an imaging optical system suitable for prevention.

  In the imaging optical system, a parallel light beam portion is provided in the optical system for various purposes. For example, an afocal optical system may be inserted into this parallel light flux section to change the focal length of the entire lens system. However, a split prism is inserted to guide a part of the light flux to the viewfinder system, or for autofocus measurement. In some cases, the optical system is guided to a distance optical system or used for another imaging system. Furthermore, an optical member that gives a special effect to the image such as a filter may be inserted.

  Thus, when an optical member having a plane substantially orthogonal to the optical axis such as a filter or a prism (hereinafter referred to as a plane member) is inserted into the parallel light flux portion, the surface of the image sensor and the plane member Ghosts due to reflections on the plane are problematic. Ghost is because part of the light imaged on the imaging surface is returned to the imaging optical system with the imaging surface as the first reflecting surface, reflected once or more in the imaging optical system, and reaches the imaging surface again. Occurs. In particular, since an image pickup device such as a CCD has a higher surface reflectance than a film or the like, reflected light from the surface of the device tends to be strong.

FIG. 6 is a schematic diagram for explaining the occurrence of a ghost. The imaging optical system schematically illustrated in FIG. 6 includes lenses L _{1 to} L ₃ and converges a light beam to an imaging position P on the imaging surface 101 of the imaging device. In addition, a half prism 102 is provided as a planar member in the parallel light beam portion C between the lens L ₂ and the lens L ₃ , and the light beam is divided by the half prism 102 into the first imaging surface side and the second imaging surface side. Is done.

Here, in the case where a plane that is substantially orthogonal to the optical axis X exists in the light beam parallel part C, the ghost in question passes through the same path after the reflected light beam from the imaging surface 101 is reflected by this plane. This is caused by reaching the imaging surface 101 again. For example, the principal ray proceeding to the l ₁ direction is incident to the imaging surface 101, partially reflected, the process proceeds to l _2, l ₃ directions, substantially orthogonal to the optical axis X arranged on the light beam parallel portion C Further, a part of the first imaging surface side plane 103 and the object side plane 104 of the half prism 102 is re-reflected and reversely travels in the l ₂ and l ₃ directions and reaches the imaging surface 101 again.

  When an imaging device such as a CCD is used and there is a plane substantially perpendicular to the optical axis X in the light beam parallel part C, the reflectance is high on all surfaces. The ghost generated in the above has a considerably large amount of light, and the image quality of the display image may be significantly deteriorated if it is left as it is.

  Conventionally, as a ghost prevention method, for example, a method of adding an antireflection coating to a planar member is known. Patent Document 1 below describes a technique for reducing reflected light by applying an antireflection coating to the surface of a flat filter. However, with this method, about 0.1 to 0.2% of the reflected light remains, so when shooting a subject with a large amount of light such as a car light or sunlight, the reflected light also becomes strong and becomes a ghost that cannot be ignored on the screen. appear. Therefore, when the performance required for video cameras and digital cameras becomes high, even this level of residual reflectance becomes unacceptable, and drastic improvement is required.

  As another ghost prevention method, a method of making the surface of a planar member non-planar has been proposed. For example, Patent Document 2 below describes forming a single plate-like filter in a curved shape. However, such a filter is difficult to process, and it is necessary to create a new filter, so that there is a problem that the cost is higher when an existing filter is used.

  Therefore, the applicant of the present application makes the surface on the planar member side a flat surface and the other surface a curved surface with respect to the planar member disposed in the parallel light flux portion, and is optically equivalent to the planar member. A method of attaching a ghost prevention member using a glass material has already been proposed (see Patent Document 3 below).

  According to this method, the light beam reflected by the surface of the image sensor and re-reflected by the curved surface of the ghost preventing member is diffused in a considerably wider range than the target image even if part of the light beam reaches the image pickup surface again. This method is an excellent method because an existing plano-convex lens may be used as a ghost prevention member, and ghosting can be easily and inexpensively reduced.

JP 2000-36917 A JP 2000-249820 A JP 2003-110891 A

  However, in the method described in Patent Document 3, the light reflected by the imaging surface and re-reflected by the curved surface of the ghost prevention member is less likely to be returned light to the imaging surface. Of the light reflected at, return light to the imaging surface due to light transmitted through the curved surface of the ghost prevention member becomes a problem.

  That is, even if the refractive indexes of the glass materials constituting the ghost preventing member and the planar member such as the half prism are matched, an adhesive layer is interposed between these two members. Unless the refractive index of the adhesive is matched, it is difficult to suppress reflection at the interface between the ghost preventing member and the planar member. However, in practice, it is extremely difficult to accurately match the refractive index of the glass material and the refractive index of the adhesive. For example, the refractive index Nd for d-line of BK7, which is extremely inexpensive as a glass glass material, is 1.516. Even if an epoxy resin having a small difference in refractive index is selected as the adhesive, the refractive index Nd for the d-line is 1.56. Therefore, a difference in refractive index of 0.04 or more is generated between the two, and eventually 0.02% of return light is generated at the interface. Of course, similar return light is also generated between the flat member such as a half prism and the adhesive layer, so that about 0.04% of return light is generated in total.

  In the current situation where there is a growing demand for image quality improvement, even a ghost with a return light of about 0.04% is a big problem to be improved.

  The present invention has been made in view of such circumstances, and reflected light generated at the interface between the plane of the optical member and the adhesive layer provided on the plane can be significantly suppressed with a simple configuration. An object of the present invention is to provide an optical reflection preventing optical system and an imaging optical system.

  The light reflection preventing optical system of the present invention is characterized in that a light reflection preventing film composed of a multilayer film is provided between an optical member and an adhesive layer provided on the plane of the optical member. .

  Here, the light reflection preventing optical system is preferably used when the refractive index difference between the glass material constituting the optical member and the adhesive constituting the adhesive layer is set to a value within 0.1. .

Further, the imaging optical system of the present invention is an optical having at least one plane that is disposed in a luminous flux region in which the central luminous flux is substantially parallel to the optical axis on the object side of the imaging element, and is substantially orthogonal to the optical axis. Comprising a member,
A ghost prevention member formed of a glass material having optically equivalent characteristics as the optical member and having a curved surface on the imaging element side is adhered to at least one plane of the optical member by an adhesive layer. In the imaging optical system,
A light reflection preventing film having a multilayer structure is provided between at least one of the ghost preventing member and the adhesive layer and between the optical member and the adhesive layer.

  Here, the imaging optical system includes a refractive index difference between a glass material constituting the ghost prevention member and an adhesive constituting the adhesive layer, and a glass material constituting the optical member and an adhesive constituting the adhesive layer. It is preferable to use when the difference in refractive index is within 0.1.

  Furthermore, in the imaging optical system, the optical member is a prism for splitting a light beam, and splits the light beam incident from the incident side plane into first and second emitted light beams, and the first emitted light beam Are emitted from the first emission side plane toward the image pickup device, and the second emission light beam is emitted from the second emission side plane toward the sensor unit for autofocus adjustment. The ghost prevention member is bonded to at least one of the two emission side planes via an adhesive layer, and a multilayer is provided between the prism and the adhesive layer and at least one between the ghost prevention member and the adhesive layer. It is preferable to provide an antireflection film made of a film.

  The “adhesive layer” is not only an adhesive layer used for adhering an optical member and another member, but also, for example, a light absorbing film containing an adhesive (for example, described in Japanese Patent Application No. 2003-332398) The light-absorbing film is a broad concept.

  According to the light reflection preventing optical system and the image pickup optical system of the present invention, the reflection preventing film made of a multilayer film having a light reflection preventing effect at the interface between the plane of the optical member and the adhesive layer provided on the plane. Even if there is a difference in refractive index between the optical member and the adhesive layer forming member, it is possible to suppress the reflection of light rays that have conventionally occurred at the interface between the optical member and the adhesive layer. Can be reliably suppressed.

Hereinafter, specific embodiments of the present invention will be described with reference to the drawings. In each drawing, the thickness of each layer is exaggerated for convenience of explanation. The imaging optical system of the embodiment shown in FIG. 1 is mounted on a camera device (for example, a digital camera), and a light beam is coupled on the imaging surface 1 of the imaging element by lenses L _{1 to} L ₃ schematically represented. It converges to the image position P. A half prism 2 is disposed between the lens L ₂ and the lens L _{3 in} a parallel light beam portion C in which the central light beam is substantially parallel to the optical axis. The light beam is separated from the first imaging surface side and the second light beam by the half prism 2. The image is divided and emitted on the imaging surface side. Here, the half prism 2 is an optical member (planar member) in which both surfaces 3 and 4 on the object side and the first imaging surface side are formed as planes substantially orthogonal to the optical axis. Ghost preventing members 5 and 6 are bonded to both flat surfaces 3 and 4 of the flat member, respectively, and the flat member and both ghost preventing members 5 and 6 constitute an adhesive body. The ghost preventing members 5 and 6 are each made of a glass material that is optically equivalent to the flat member, and the surface opposite to the bonding surface is a lens surface having a large curvature radius.

  Here, the “lens surface having a large radius of curvature” means that the surface has no power and does not affect the parallel light flux. The power of a certain level varies depending on the performance of the optical system and the curvature of each surface, and is not necessarily expressed as a specific numerical value. Although the surface opposite to the adhesion surface of the ghost preventing members 5 and 6 is a convex surface, it can be replaced with a concave surface.

The first ghost prevention function having such a configuration will be described with the ghost prevention member 5 as a representative. In the imaging optical system shown in FIG. 1, considering the optical path of the reflected light beam from the imaging surface 1, for example, the chief ray traveling in the l ₁ direction is partially reflected after entering the imaging device, Advancing in the l ₂ and l ₃ directions, a part of the lens surface of the ghost preventing member 5 is further reflected again. Since this surface is a lens surface (convex surface in FIG. 1), the principal ray travels in the l ₄ and l ₅ directions. That is, since this principal ray is re-reflected by the lens surface of the ghost prevention member 5, it does not reverse the same path as the principal ray going from the imaging surface 1 to the lens surface. Therefore, even if a part of these re-reflected light reaches the imaging surface 1 again, the generated light image hardly affects the image.

However, on the other hand, the light beam reflected by the imaging surface 1 and transmitted through the lens surface of the ghost preventing member 5 reaches the flat surface of the ghost preventing member 5 on the half prism 2 side or the flat surface 3 of the half prism 2, and a part thereof. Are reflected in these planes (hereinafter referred to as plane 3 etc.). That is, the principal ray reflected by the imaging surface 1, traveling in the l ₂ and l ₃ directions, and transmitted through the lens surface of the anti-ghosting member 5 is incident on these planes 3 and the like perpendicularly. The chief rays reflected by etc. travel so as to reverse in the l ₂ and l ₃ directions, and a part of these re-reflected light reaches the imaging surface 1 again.

  Thus, since the light rays reflected from these planes 3 and the like reach the imaging surface 1 and cause ghosts, the reflection of the light rays on the planes 3 and the like is suppressed as much as possible in order to prevent the ghosts. is necessary.

  Here, in order to suppress the reflection of light rays on the plane 3 or the like, the difference in refractive index between the ghost preventing member 5 and the adhesive layer and the difference in refractive index between the adhesive layer and the half prism 2 may be zero. Actually, it is difficult to match the refractive index of the glass material constituting the ghost preventing member 5 and the half prism 2 with the refractive index of the adhesive constituting the adhesive layer. That is, for example, the refractive index Nd for the d-line of BK7, which is extremely inexpensive as a glass glass material, is 1.516, and even if an epoxy resin having a small refractive index difference is selected as the adhesive, the refractive index Nd for the d-line is 1.56. A refractive index difference of 0.04 or more is generated between the two. As a result, about 0.02% of return light is generated at the interface between the ghost prevention member 5 and the adhesive layer, and the interface between the adhesive layer and the half prism 2, and about 0.04% of return light is generated. . As described above, if this return light cannot be suppressed, the generation of ghost cannot be suppressed reliably.

  Therefore, in the present embodiment, the occurrence of the ghost described above is reliably suppressed by having a second ghost prevention function as described below.

  That is, in the present embodiment, as shown in the circle of FIG. 1, multilayer antireflection films 21 are provided at the interface between the ghost preventing member 5 and the adhesive layer 23 and at the interface between the adhesive layer 23 and the half prism 2, respectively. , 22 are interposed. The formation method includes a multilayer antireflection film 21 on the flat surface 13 of the ghost prevention member 5 and a multilayer antireflection film 22 on the flat surface 3 of the half prism 2. A film is formed by a forming method, and the two flat surfaces 13 and 3 on which the antireflection films 21 and 22 are formed are bonded using an adhesive layer 23.

The ghost preventing member 5, the adhesive layer 23, and the antireflection film 21 (or the half prism 2, the adhesive layer 23, and the antireflection film 22) constitute the light reflection preventing optical system according to the embodiment of the present invention.
Here, the glass material constituting the ghost prevention member 5 and half prism 2 is a BK7, refractive index n ₁ with respect to the d line is 1.516 as mentioned above, also the adhesive constituting the adhesive layer 23 is an epoxy resin The refractive index n ₂ for the d line is 1.56 as described above.

FIG. 2 is an enlarged view of only the interface portion between the ghost preventing member 5 and the adhesive layer 23. As shown in the figure, the antireflection film 21 is formed on the flat surface 13 of the ghost prevention member 5 with an SiO ₂ layer 21a (refractive index n = 1.46, 4nd = 48 nm when the geometric thickness is d), Al ₂ O _3. The layer 21b (refractive index n = 1.60, 4nd = 112 nm when the geometric thickness is d), and the SiO ₂ layer 21c (refractive index n = 1.46, 4nd = 72 nm, when the geometric thickness is d) are sequentially formed. A multilayer film having a three-layer structure formed by laminating. In FIG. 2, a light beam 31 traveling from an object to the image sensor and a light beam 32 reflected by the image sensor are schematically shown.

The antireflection film 21 has a sandwich structure in which an Al ₂ O ₃ layer 21b having a large refractive index is sandwiched between SiO ₂ layers 21a and 21c having a small refractive index, and the thickness of each layer generates reflected light due to the light interference effect. It is set to a value that can be suppressed. Due to the light reflection preventing effect of the antireflection film 21, even if a refractive index difference occurs between the formation members of the ghost prevention member 5 and the adhesive layer 23, at the interface between the ghost prevention member 5 and the adhesive layer 23, It is possible to suppress the reflection of light rays that has conventionally occurred, and to suppress the occurrence of the ghost.

  Similarly, by interposing the antireflection film 22 between the adhesive layer 23 and the half prism 2, it is possible to suppress the reflection of light rays that has conventionally occurred at the interface between the adhesive layer 23 and the half prism 2, Generation of the ghost can be reliably suppressed.

  In addition, as described above, in the present embodiment, the object-side surface 4 of the half prism 2 is also an optical member (planar member) that is a plane substantially orthogonal to the optical axis. A ghost prevention member 6 is also adhered to the flat surface 4 of the same, and a multilayer antireflection film similar to the antireflection films 21 and 22 is provided between the ghost prevention member 6 and the adhesive layer and between the adhesive layer and the half prism 2. A film is provided. Accordingly, the first ghost prevention function and the second ghost prevention function are exhibited also in the region between the half prism 2 and the ghost prevention member 6, and the generation of ghost can be reliably suppressed. Yes.

  FIG. 3 shows the ghost prevention member 5 and the adhesive layer 23 of the prior art having only the first ghost prevention function and the present embodiment having the first ghost prevention function and the second ghost prevention function. It is a graph which shows the reflectance of the light ray in the interface. As shown in FIG. 3, in the conventional technology, the light reflectance can be suppressed only to about 0.02% in the entire visible light wavelength region, whereas in the present embodiment, in the total visible light wavelength region. Therefore, the light reflectance can be suppressed to about 0.01% or less, and particularly in the vicinity of the wavelength region of 510 nm, the light reflectance can be as extremely small as about 0.000425%.

  Therefore, in the present embodiment, it is possible to achieve a great effect even when used over the entire visible light wavelength region. be able to.

  Note that the layer configuration of the antireflection films 21 and 22 is not limited to that of the above-described embodiment, and can of course be changed to various layer configurations having an antireflection function due to an optical interference effect. The wavelength of the minimum reflectance can be arbitrarily set by such a change.

  The light reflection preventing optical system and the imaging optical system of the present invention are not limited to those of the above-described embodiment, and various other modes can be changed.

  For example, in the above-described embodiment, the ghost prevention members 5 and 6 are bonded to the two flat surfaces 3 and 4 of the flat member, respectively, and the first and second ghost prevention members 5 and 6 are connected to each other. Although the multilayer antireflection films 21 and 22 capable of exhibiting the ghost prevention function 2 are provided, the multilayer antireflection films 21 and 22 may be provided only on one of them. As shown in FIG. 4, a ghost prevention member 9 is bonded to the plane 8 on the second imaging surface side of the plane member, and a multilayer capable of exhibiting the second ghost prevention function between the plane 8 and the ghost prevention member 9. An antireflection film may be provided.

  Furthermore, it is possible to provide the multilayer antireflection film only between either one of the optical members to be bonded and the adhesive layer.

  Further, the antireflection optical system of the present invention can be applied to various optical systems other than the imaging optical system as described above. For example, as shown in FIG. 5 (some elements are shown separated from each other for the sake of convenience), a transmissive optical member 45 and a reflective optical member 41 (formed by forming a reflective film 47 on the substrate 42) are provided. When bonding by the adhesive layer 23, a multilayer antireflection film 21 (21 a, 21 b, 21 c) is formed on the flat surface 43 of the transmission optical member 45, and the transmission optical member 45 and the adhesive layer 23 are It is also possible to suppress unnecessary reflected light 53 at the interface between them. Thereby, the noise component of the light 52 reflected from the reflective optical member 41 can be reduced. Furthermore, the configuration of the present invention can also be applied to the case where a light absorbing film containing an adhesive (included in the concept of an adhesive layer in the present invention) is provided on a transmission optical member.

  For example, Japanese Patent Laid-Open No. 62-78501 discloses a technique in which a single-layer antireflection film is formed on an optical member and an adhesive is applied thereon. The target reflectance, its purpose, function and effect are completely different from those of the present invention.

1 is a configuration diagram of an imaging optical system according to an embodiment of the present invention. FIG. 1 is an enlarged conceptual view of a part of the imaging optical system shown in FIG. The graph which shows the light reflectivity in the interface of a ghost prevention member and a contact bonding layer in both a prior art and this embodiment. The graph which shows the partial change aspect of embodiment shown in FIG. Schematic showing an embodiment different from the embodiment shown in FIG. Configuration diagram of imaging optical system according to prior art

Explanation of symbols

L _{1 to} L ₃ lenses _1, 101 Imaging surface 2, 102 Half prism (planar member)
3, 4, 8, 13, 43, 103, 104 Plane 5, 6, 9, 105, 106 Anti-ghost member 21, 22 Anti-reflection film 21a, 21c SiO ₂ layer 21b Al ₂ O ₃ layer 23 Adhesive layer 41 Reflective optics 41 Member 45 Transmission optical member X Optical axis C Parallel light flux P Imaging position

Claims (5)

  A light reflection preventing optical system, wherein a light reflection preventing film composed of a multilayer film is provided between an optical member and an adhesive layer provided on a plane of the optical member.   2. The light reflection preventing optical system according to claim 1, wherein a difference in refractive index between the glass material constituting the optical member and the adhesive constituting the adhesive layer is a value within 0.1. An optical member having at least one plane substantially perpendicular to the optical axis, which is disposed in a light flux region in which the central light flux is substantially parallel to the optical axis on the object side of the image sensor;
A ghost prevention member formed of a glass material having optically equivalent characteristics as the optical member and having a curved surface on the imaging element side is adhered to at least one plane of the optical member by an adhesive layer. In the imaging optical system,
An imaging optical system comprising a multi-layered antireflection film provided between at least one of the ghost prevention member and the adhesive layer and between the optical member and the adhesive layer.   The refractive index difference between the glass material constituting the ghost preventing member and the adhesive constituting the adhesive layer, and the refractive index difference between the glass material constituting the optical member and the adhesive constituting the adhesive layer are within 0.1. The imaging optical system according to claim 3, wherein   The optical member is a prism for splitting a light beam, and splits the light beam incident from the incident side plane into first and second light beams, and the first light beam is imaged from the first emission side plane. The light is emitted toward the element, and the second light flux is emitted from the second emission side plane toward the sensor unit for autofocus adjustment. An adhesive layer is provided on at least one of these two emission side planes. The anti-ghost member is bonded, and an anti-reflection film composed of a multilayer film is provided between at least one of the prism and the adhesive layer and between the anti-ghost member and the adhesive layer. The imaging optical system according to claim 3 or 4, wherein the imaging optical system is characterized in that:

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