JP2000249820A - Filter and lens barrel - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a filter by which the deterioration of an image quality due to a ghost caused at the time of attaching the filter is reduced without largely impairing the optical performance of an image pickup lens. SOLUTION: An object side surface and an image side surface of a light transmitting member of the filter are made into a spherical shape, and the radius of curvature and the effective diameter of a light beam satisfy the conditions of: 0<|r1|-√(r12-(a/2)2)<=5 and 0.98<r2/r1<1.02. Then, r1 and r2 respectively mean the radius of curvature of the object side surface and the image side surface of the light transmitting member and (a) means the effective diameter of the light beam of the filter.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a filter and a lens barrel, and more particularly to a detachable filter which is used by being attached to an object-side portion of a lens barrel of a photographing device such as a camera, a video camera or a digital video camera. Things.

[0002]

2. Description of the Related Art Conventionally, photographing devices such as cameras, video cameras and digital video cameras have been used by being attached to the front of a lens barrel for the purpose of protecting a photographing lens or obtaining a special photographing effect. Many removable filters are used.

[0003] For example, a protection filter for protecting a lens, dimming of photographing light and an ND which provides a special photographing effect.
Filters, color temperature conversion filters, polarizing filters,
Foggy filters, color image filters, etc.
The types vary depending on the purpose of use and the configuration.

On the other hand, as a recent new technology, a substantially transparent hydrophilic or water-absorbing function as disclosed in JP-A-9-230106, JP-A-10-311902 and the like has been disclosed. A technology has been proposed in which a camera filter is provided with an anti-fog effect by a technique for obtaining an anti-fog effect by providing a film on the surface of an optical member.

[0005]

In the filter having the above-described anti-fogging effect, it is necessary to provide a functional film having the anti-fogging effect and an anti-reflection film which greatly affects the image quality on the optical member surface. This is an important technical issue.

For example, in the technique disclosed in Japanese Patent Application Laid-Open No. 10-311902, the moisture adhering to the surface of the filter is adopted by employing a laminated structure of an antifogging film made of a water-absorbing polymer and a porous antireflection film. And an anti-reflection film that suppresses the reflected light generated at the interface with the outside air are proposed to provide an effective anti-fogging anti-reflection film.

[0007] On the other hand, in order to achieve both satisfactory anti-reflection properties and anti-fogging properties, high precision is required for the composition and production of the film, and the flexibility of the film composition is lost.

[0008] However, if the antireflection property is reduced so much as to give priority to the antifogging property, an image obtained by photographing will be greatly affected.

In general, when the individual optical elements constituting the photographing optical system do not have sufficient anti-reflection properties, the amount of light that reaches the imaging surface due to the reflection of the incident light beam on each surface of the optical system, A phenomenon called so-called ghost occurs in which the light beam repeatedly reflected inside the optical system reaches the imaging surface.

[0010] In particular, with regard to this ghost, when the above-described detachable camera filter is used, most of the ghost is constituted by a flat plate in which the light transmitting member of the filter is arranged in parallel with the imaging surface. , Its impact is great,
For example, when an incident light beam reflected on the imaging surface is reflected again on one surface of the filter and a ghost is generated, the ghost follows the optical path shown in FIG. The image quality of the obtained image is greatly reduced. This phenomenon is particularly conspicuous when a strong light source exists in the object scene.

However, on the other hand, the effect of the antireflection film, which is widely and generally used at present, is not so large that reflected light can be completely eliminated in a wide light wavelength range required for photography. Even if a film with high anti-reflection properties is configured on one surface of the filter,
It does not completely prevent ghosting that occurs when there is a strong light source in the field.

Further, in the case where an imaging device having an imaging device such as a CCD such as a digital camera, which is rapidly spreading in recent years, is used on the imaging surface, the reflectance of the imaging device itself, which is the imaging surface, is limited to a silver halide film. As a result, the ghost caused by internal reflection necessarily appears more clearly on the image pickup surface, and the image quality of the obtained image is significantly reduced.

An object of the invention according to the present application is to provide a filter capable of reducing a deterioration in image quality due to a ghost generated when the filter is mounted without significantly impairing the optical performance of the imaging lens.

Another object of the present invention according to the present application is to provide a filter and a filter having a high degree of freedom in film configuration without requiring a high antireflection property for the film itself in addition to the above objects. It is an object of the present invention to provide a lens barrel having the following.

[0015]

According to a first aspect of the present invention, there is provided a filter in which the object side surface and the image side surface of a light transmitting member are formed into curved surfaces.

A second configuration of the filter for realizing the object of the invention according to the present application is one in which the object side surface and the image side surface of the light transmitting member are formed into spherical surfaces.

A third configuration of the filter for realizing the object of the invention according to the present application is one in which the object side surface of the light transmitting member is formed as a convex surface and the image side surface is formed as a concave surface.

A fourth configuration of a filter for realizing the object of the invention according to the present application is a filter detachably mounted on the object side of a lens barrel, wherein a light transmitting member has a plane parallel to an imaging plane of the lens. Is not provided.

According to a fifth configuration of the filter for realizing the object of the invention according to the present application, in the fifth configuration, the object side surface and the image side surface of the light transmitting member of the filter are spherical, and the radius of curvature thereof is And the effective beam diameter satisfies the following conditions.

[0020] 0 <| r1 | -√ (r1 2 - (a / 2) 2) ≦ 5 0.98 <r2 / r1 <1.02 where, r1, r2, respectively, the object side surface of the light transmitting member,
The radius of curvature of the image side surface, a, is the effective beam diameter of the filter.

According to a sixth configuration of the filter for realizing the object of the invention according to the present application, in the fourth or fifth configuration, the light transmitting member is formed such that the object side surface is formed as a convex surface and the image side surface is formed as a concave surface. Is what it is.

According to a seventh aspect of the present invention, there is provided a filter according to any one of the above aspects, wherein at least one surface of the light transmitting member has substantially transparent hydrophilicity or water absorption. It has a surface layer that has it.

The structure of the lens barrel for realizing the object of the invention according to the present application is such that a filter having any one of the above structures is provided on the object side of the lens.

[0024]

DESCRIPTION OF THE PREFERRED EMBODIMENTS (First Embodiment) FIG. 1 shows a first embodiment of the present invention.

FIG. 1 is a sectional view of a filter according to the present embodiment.

The filter according to the present embodiment has a light transmitting member 7 held by a filter frame 8 in which the object side surface and the emission side are formed into a spherical curved surface. For example, as shown in FIG. 2 is detachably attached to the object side.

In FIG. 2, 3 is an aperture, 4 is an imaging surface,
Denotes an incident light beam and an optical path reflected by the imaging surface, and 6 denotes an optical path of a ghost light beam reflected by the filter surface and reaching the imaging surface again.

That is, the object side surface and the image side surface of the light transmitting member 7 of the filter do not have a plane parallel to the imaging plane of the imaging lens to which the filter is mounted.

Further, as shown in FIGS. 3 and 4, the curvature of the object side surface R1 and the curvature of the image side surface R2 of the light transmitting member 7 are not limited to fixed values. Is determined by

As shown in FIGS. 2 and 11, the luminous flux that has reached the filter surface after being reflected on the image plane is reflected at each point on the light transmitting member surface of the filter by an angle defined by the radiation line of that surface as the axis of symmetry. , And passes through the imaging lens to reach the imaging surface.

For this reason, when the filter surface has a spherical shape, the larger the curvature of the surface, the larger the reflection angle at the time of reflection at each point of the filter surface. As a result, the image position of the ghost light is farther from the image surface, and The divergence of the ghost light on the image plane increases.

That is, in order to make the ghost on the image plane less noticeable, the curvature given to the light transmitting member should be increased (the radius of curvature should be reduced).

However, as the curvature given to the surface increases,
The performance of the imaging lens, such as spherical aberration and astigmatism, is affected.At the same time, the light transmitting member of the filter becomes largely convex in the optical axis direction, which makes it inconvenient to handle. Needs to be limited to a certain range.

Further, in order not to affect the performance of the imaging lens, it is necessary that the curvature of the object side surface R1 and the curvature of the image side surface R2 are substantially equal. If they are far apart, the refracting power of the filter itself with respect to the incident light beam increases, which also affects the optical performance of the imaging lens.

From this point of view, the present invention expresses the condition of the radius of curvature given to the filter surface by a value (here, the convex amount of the filter surface in the optical axis direction) in relation to the effective beam diameter. And limiting the ratio of the curvature of the object side surface R1 to the curvature of the image side surface R2 within a certain range, the condition of the filter shape that does not significantly affect the performance of the imaging lens and that is effective for the ghost reduction effect is reduced. Have given. As described above, by forming the filter surface into a curved shape, the light beam reflected on the imaging surface 4 shown by the optical path 5 reaches the filter surface from the imaging surface after being reflected again by the light transmitting member 7 of the filter shown by the optical path 6. The imaging relationship that reaches the imaging surface following substantially the same optical path as the luminous flux collapses, and the possibility that ghost light forms an image on the imaging surface becomes extremely low.

In particular, when the light transmitting member of the filter is formed into a spherical shape having a certain radius of curvature, the image forming position of the ghost light can be moved to an arbitrary position away from the imaging surface as shown in FIG. By making the ghost light reaching the imaging surface sufficiently diverged, it is possible to make the ghost almost unrecognizable on the obtained image or video.

The filter according to the present embodiment is characterized in that the object side surface and the image side surface of the light transmitting member are spherical, and the radius of curvature and the effective beam diameter satisfy the following conditional expressions.

As shown in FIG. 12, when the effective diameter is a and the radius of curvature is R, the convex amount of the filter is Rx (virtual distance).

From the theorem of three squares, from x ² + (a / 2) ² = R ² , x = √ [R ^2- (a / 2) ² ] Convex amount = R−x = R−√ [R ² − (A / 2) ² ].

Here, the radius of curvature is the direction of curvature, and
Since “+” and “−” are added, the radius of curvature is an absolute value.

From the above equation, the convexity is in the following range.

[0042] 0 <| r1 | -√ (r1 2 - (a / 2) 2) ≦ 5 ··· 0.98 <r2 / r1 <1.02 ··· However, r1, r2, respectively, of the filter The radius of curvature of the object side surface and the image side surface of the light transmitting member serving as the substrate, and a is the effective beam diameter of the filter.

The direction of curvature at this time is not particularly limited.
The light transmitting member may have a convex shape on the object side or a convex shape on the image side.

If the lower limit of the above equation is exceeded (that is, if it becomes 0), r1 becomes a plane, and the effect of ghost reduction is lost. When the value exceeds the upper limit, various aberrations and other optical performances of the imaging lens are greatly changed due to an increase in curvature.

When the ratio of the radius of curvature between the object side surface and the image side surface of the filter exceeds the range of the expression, the refractive power of the filter lens gradually increases to a level that cannot be ignored. This will affect the performance of the lens. At the same time, it changes the focal length and focus position of the imaging lens with the filter attached,
If the distance deviates significantly from this range, the focus position changes greatly, which may adversely affect the focus adjustment function of the imaging lens.

Ideally, the relationship between the radius of curvature of the object side surface and that of the image side surface should satisfy the following equation.

This is a conditional expression that the refractive power of the single lens with respect to the incident light beam is almost zero.

R2 = r1−d (1 + 1 / N) where r1 and r2 are the radius of curvature of the object side surface and the image side surface of the light transmitting member serving as the substrate of the filter, and d is the optical axis of the filter. The upper thickness, N, is the refractive index of the light transmitting member 7.

The expression is a condition for preventing the relationship between the curvature of the object side surface and the curvature of the image side from deviating significantly from the expression.

Further, the filter of the present embodiment is characterized in that both the object side surface and the image side surface have a curvature that is convex toward the object side.

Thus, even when the object-side surface of the imaging lens to which the filter is attached has the largest object-side surface and a convex shape toward the object side, the light-transmitting member of the filter and the imaging lens do not come into contact with each other and cause no damage. . Further, even when the same absolute amount of curvature is given, the divergence of the luminous flux when reaching the imaging surface is greater than when a convex shape is given on the image side, so that the efficiency of the ghost reduction effect increases.

Further, as a more desirable form of the camera filter according to the present invention, it is required that the radius of curvature given to the light transmitting member of the filter is further in the range of the following expression.

[0053] 0 <| r1 | -√ - content represented by ^{(r1 2 (a / 2)} 2) <3 ··· conditions symbols in formula are as defined above.

In the above formulas and formulas, the value of the central term represents the amount of protrusion of the light transmitting member serving as the filter substrate.
If this value is too large, the apex of the filter lens that is convex toward the object side will protrude from the tip of the filter frame that fixes it, and it is more likely that the filter lens will be damaged during use. It is inconvenient. If the filter frame is configured to protrude toward the object side so as to cover the convexity of the lens according to the shape of the filter lens according to the present invention, the above problem can be solved.However, when the amount of protrusion of the frame increases, the frame itself becomes a filter. Oblique rays around the incident off-axis image may be blocked and vignetting may occur.
By satisfying the condition of the expression, the convexity of the filter lens can be suppressed, and the above-mentioned problems do not occur even if the filter lens according to the present invention is incorporated in a frame of a flat filter which is widely used at present.

The effect of reducing the ghost, that is, the degree of divergence of the ghost light on the image pickup surface increases as the radius of curvature applied to the filter decreases. However, as the radius of curvature decreases, the change in the performance of the imaging lens to which the filter is attached tends to increase, and at the same time, the convexity of the filter also increases, causing handling problems. Since these vary depending on the configuration of the imaging lens to be mounted and the focal length, an appropriate radius of curvature may be selected in each case within the range of the above conditions.

According to the above technique, by giving an appropriate shape to the light transmitting member of the camera filter, it is possible to reduce ghost on the image pickup surface which occurs when the filter is attached to the image pickup lens.

At the same time, this technology partially plays a role of the antireflection film provided on the surface of the light transmitting member.
That is, this is a technique in which the ghost reduction effect can be imparted to the light transmitting member itself.

[0058]

FIG. 5 shows various aberrations of the optical system shown in FIG.
The data is shown in FIG.

Embodiment 2: Various aberrations of the optical system of FIG. 3 are shown in FIG.
FIG. 9 shows the data.

Embodiment 3: FIG. 7 shows various aberrations of the optical system shown in FIG.
FIG. 10 shows the data.

Note that the first to third embodiments shown in FIGS.
The meanings of the symbols in the data are as follows.

Ri is the radius of curvature of the i-th surface from the object side. In each embodiment, r1 to r2 are filter portions, and r3 and subsequent portions are the imaging lens portions to which the filters are attached. r1, r
2 is the radius of curvature of the object side surface and the image side surface of the filter, respectively.

Di is the i-th surface from the object side and the (i + 1) th surface
The face spacing of the i-th face, ni and vi are the i-th face and i +
The refractive index and Abbe number at the d-line (λ = 587.6 nm) of the medium between the first surfaces.

(Second Embodiment) A filter according to a second embodiment of the present invention has a substantially transparent hydrophilic or water-absorbing surface on at least one surface of the light transmitting member surface of the filter satisfying the above-described conditions. An anti-fogging camera with an anti-fogging anti-reflection film with a high degree of freedom in film configuration, which has anti-fogging performance by providing a surface layer with Filter.

[0065]

As described above, according to the present invention, by giving an appropriate curvature to the light transmitting member serving as the substrate of the filter, the light appears on the imaging surface without greatly changing the optical performance of the imaging lens to be mounted. Ghost effects can be reduced.

Further, according to this technique, the function of reducing ghost can be performed by the light transmitting member serving as the substrate of the filter, so that the film itself does not need to have a high antireflection property, and the degree of freedom of the film configuration is increased. A high antifogging antireflection film and a camera filter having the antifogging property provided with the antifogging film can be realized.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a filter according to a first embodiment of the present invention.

FIG. 2 illustrates an optical system according to a first exemplary embodiment.

FIG. 3 illustrates an optical system according to a second embodiment.

FIG. 4 illustrates an optical system according to a third embodiment.

FIG. 5 is a diagram illustrating various aberrations of the optical system according to the first exemplary embodiment.

FIG. 6 is a diagram illustrating various aberrations of the optical system according to the second embodiment.

FIG. 7 illustrates various aberrations of the optical system according to the third embodiment.

FIG. 8 is a diagram showing data of Example 1.

FIG. 9 is a diagram showing data of Example 2.

FIG. 10 is a diagram showing data of Example 3.

FIG. 11 is a diagram showing a photographing lens optical system using a conventional filter.

FIG. 12 is a diagram for calculating a convex amount of the filter of the present invention.

[Explanation of symbols]

Reference Signs List 1 light transmitting member 2 imaging lens optical unit 3 aperture 4 imaging surface 5 optical path of incident light beam and light beam reflected on the imaging surface (substantially overlapping with incident light beam) 6 ghost light beam reflected on filter surface and reaching image pickup surface again 7 Light transmitting member of filter according to the present invention 8 Filter frame R1 Object side surface of light transmitting member R2 Image side surface of light transmitting member

Claims (8)

[Claims] 1. A filter characterized in that the object side surface and the image side surface of the light transmitting member are formed as curved surfaces. 2. A filter, wherein the object side surface and the image side surface of the light transmitting member are formed into spherical surfaces. 3. A filter wherein the object side surface of the light transmitting member is formed as a convex surface and the image side surface is formed as a concave surface. 4. A filter detachably mounted on an object side of a lens barrel, wherein a light transmitting member does not have a plane parallel to the lens or its imaging plane. 5. The filter according to claim 5, wherein the object side surface and the image side surface of the light transmitting member of the filter have a spherical shape, and the radius of curvature and the effective beam diameter satisfy the following conditions. 0 <| r1 | -√ (r1 2 - (a / 2) 2) ≦ 5 0.98 <r2 / r1 <1.02 where, r1, r2, respectively, the object side surface of the light transmitting member,
The radius of curvature of the image side surface, a, is the effective beam diameter of the filter. 6. The light transmitting member according to claim 4, wherein an object side surface is formed as a convex surface, and an image side surface is formed as a concave surface.
Or the filter according to 5. 7. A light-transmitting member according to claim 1, wherein a substantially transparent hydrophilic or water-absorbing surface layer is formed on at least one surface of the light transmitting member. filter. 8. A lens barrel, wherein the filter according to claim 1 is provided on the object side of the lens.