JP2006091430A - Lens unit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To specify, in a lens unit in which a ceramic lens is mounted, a positional relation between a ceramic lens and an imaging element so that a void has no adverse effect on a photographed image. <P>SOLUTION: In the lens unit 1 having a photographic lens and the imaging element, the photographic lens is the ceramic lens 2. Where a distance from the image plane 31 of the imaging element 3 to the lens face of the ceramic lens 2 is d, the radius of the void 4 in the ceramic lens 2 is r, and the F value of the ceramic lens 2 is F, the distance d satisfies the conditional expression (1). <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a lens unit equipped with a ceramic lens mainly used in a small-sized imaging device using an imaging element such as a CCD such as a digital still camera, a surveillance camera, and a PC camera attached to a personal computer.

  In recent years, digital still cameras for general use (hereinafter referred to as DSC) are rapidly spreading. The DSC is an image pickup apparatus that structurally captures a still image formed by a photographing lens with an image pickup device such as a CCD (Charged Coupled Device) and records it in a built-in memory or a memory card.

By the way, as a photographic lens used for DSC (for example, refer to Patent Document 1, etc.), a photographic lens made of glass or plastic has been conventionally used. However, recently, a small ceramic lens has been developed, and it is expected that the performance of the DSC will be further improved by applying it to the DSC.
JP 2002-228922 A

  However, in a ceramic lens, very fine bubbles called voids are generated in the lens at the manufacturing stage, but a method for removing voids from the lens has not yet been established. Therefore, at the present time, it is inevitable to use a ceramic lens in which a void is mixed. However, if the void is large, an effect such as blurring of an image may occur.

  Accordingly, an object of the present invention is to define the positional relationship between a ceramic lens and an image sensor so that a void does not affect a captured image in a lens unit equipped with a ceramic lens.

In order to solve the above problems, the lens unit of the present invention is:
In a lens unit comprising a photographic lens and an image sensor,
The taking lens is a ceramic lens;
When the distance from the image plane of the image sensor to the lens surface of the ceramic lens is d, the radius of the void in the ceramic lens is r, and the F value of the ceramic lens is F, the distance d is the following conditional expression: Satisfies (1).

The lens unit of the present invention viewed from another viewpoint is
In a lens unit including a plurality of photographing lenses and an image sensor,
The plurality of photographing lenses include ceramic lenses,
When the distance from the image plane of the image sensor to the lens surface of the ceramic lens is d, the radius of the void in the ceramic lens is r, and the F value of the ceramic lens is F, the distance d is the following conditional expression: Satisfies (2).

The lens unit of the present invention seen from another viewpoint is
In a lens unit including a plurality of photographing lenses and an image sensor,
The plurality of photographic lenses include a plurality of ceramic lenses,
Among the plurality of ceramic lenses, for a ceramic lens closest to the image sensor, d is a distance from the image surface of the image sensor to the lens surface, r is a radius of a void in the ceramic lens, and an F value of the ceramic lens. Is F, the distance d satisfies the following conditional expression (3).

  Preferably, the distance d is calculated by air-converting another photographic lens existing between the ceramic lens and the image sensor.

  More preferably, the ceramic lens is formed by processing translucent ceramics into a lens shape.

  According to the present invention, in the lens unit, the positional relationship between the ceramic lens and the imaging device is defined, and the movable range of the ceramic lens is limited to a range satisfying the conditional expression, thereby blurring the captured image due to voids. It is possible to effectively avoid the influence of the above, and it is possible to prevent the void from affecting the image.

  Hereinafter, the best mode for carrying out the present invention will be described in detail with reference to the drawings.

  The lens unit 1 of the present embodiment is used in an imaging unit L of a digital still camera C as shown in FIG. 1, and as schematically shown in FIG. 2, a ceramic lens 2 as a photographing lens, and imaging. A CCD element 3 as an element is provided. In this embodiment, the ceramic lens 2 is formed by processing translucent ceramics into a lens shape. In addition, as described above, the void 4 exists in the ceramic lens 2.

  As described above, when the void 4 is large, the formation of incident light on the image plane 31 of the CCD element 3 is obstructed by the void 4, and the image picked up by the CCD element 3 is affected. Therefore, in the present embodiment, the positional relationship of the ceramic lens 2 with respect to the CCD element 3, that is, the distance between the two is limited to a certain movable range, so that the influence of the void 4 is avoided. Hereinafter, the size of the void 4 is evaluated and considered as a ratio a of the cross-sectional area s of the void 4 to the area S of the region A through which the light of the ceramic lens 2 passes, as shown in FIG.

  The ratio a is expressed by the following formula (4). When the radius of the region A through which the light of the ceramic lens 2 passes is R and the radius of the void 4 is r, the cross-sectional area s of the void 4 and the area S of the region A are They are represented by the following formulas (5) and (6), respectively.

  Further, as shown in FIG. 2, when the distance from the image surface 31 of the CCD element 3 to the lens surface of the ceramic lens is d and the incident angle is α, the radius R of the region A through which the light of the ceramic lens 2 passes, The relationship between the distance d and the incident angle α is expressed by the following formula (7).

  Further, when the F value of the ceramic lens 2 is expressed by F from the definition of the F value, it is expressed as sin α = 1 / 2F. Therefore, the incident angle α is expressed by the following formula (8), which is expressed by the formula (7). Substituting into and deforming leads to the relationship of the following formula (9).

  Substituting the radius R of the equation (12) into the equation (6), the following equation (10) is obtained. From the equation (10) and the equation (5), the ratio a is expressed as the following equation (11). Can be represented. Further, when the equation (11) is solved for the distance d, the distance d is expressed by the following equation (12).

  That is, the distance d from the image surface 31 of the CCD element 3 to the lens surface of the ceramic lens and the ratio a of the cross-sectional area s of the void 4 to the area S of the region A through which the light of the ceramic lens 2 passes are expressed by the above formula ( 12).

  As described above, when the void 4 is large, that is, when the value of the ratio a is large, the influence of the formation of incident light on the image plane 31 of the CCD element 3 being inhibited by the void 4 is significant. As a result, the image picked up by the CCD element 3 is blurred. According to the experiments by the present inventors, when the ratio a is less than 0.045, the effect of blurring of the captured image is hardly visible, but when a is 0.045 or more, the image has an effect. I know that.

  Therefore, by setting the distance d to be larger than the value obtained by substituting 0.045 for a on the right side of the equation (12), that is, by setting the distance d so as to satisfy the following conditional expression (13), The influence of 4 can be avoided. In the following conditional expression (13), the radius r of the void 4 and the F value F of the ceramic lens 2 are known values.

  In the lens unit 1 of the present embodiment, the ceramic lens 2 is disposed within a movable range such that the distance d from the image surface 31 of the CCD element 3 to the lens surface satisfies the conditional expression (13). It is configured to be able to move with.

  Next, the operation of the lens unit 1 of the present embodiment will be described.

  The ceramic lens 2 in the lens unit 1 of the present embodiment moves within the lens unit as the distance d with respect to the image plane 31 of the CCD element 3 is changed by changing the zoom magnification or the like in the same manner as a normal photographing lens. However, as described above, the distance d is limited to a range that satisfies the conditional expression (13).

  As can be seen from the above consideration, by limiting the movement range of the ceramic lens 2 within this range, the ratio a of the cross-sectional area s of the void 4 to the area S of the region A through which the light of the ceramic lens 2 passes is 0. It can prevent becoming 045 or more.

  Thus, according to the lens unit 1 of the present embodiment, the positional relationship between the ceramic lens 2 and the CCD element 3 is defined, and the movable range of the ceramic lens 2 is limited to a range that satisfies the conditional expression (13). Thus, it is possible to effectively avoid the influence of blurring and the like caused by the void 4 on the image picked up by the CCD element 3, and it is possible to prevent the void 4 from affecting the image.

[Modification]
In the above embodiment, the case where only one ceramic lens 2 is arranged in the lens unit 1 has been considered. However, in the case where the lens unit 1 includes a plurality of photographing lenses, the ceramic lens 2 is obtained by the same consideration. By defining the positional relationship between the ceramic lens 2 and the CCD element 3 and limiting the movable range of the ceramic lens 2 to a range satisfying the conditional expression (13), the captured image is affected by blurring due to the void 4. Can be effectively avoided.

  Here, as a case where the lens unit 1 includes a plurality of photographing lenses, one of the plurality of photographing lenses provided in the lens unit 1 is a ceramic lens, and a plurality of photographing lenses provided in the lens unit 1. Some of them may be ceramic lenses.

  In the former case, the same effect as described above can be obtained by defining the positional relationship between the ceramic lens 2 and the CCD element 3 and limiting the movable range of the ceramic lens 2 to a range satisfying the conditional expression (13). Obtainable.

  In the latter case, the ceramic lens 2 closest to the CCD element 3 among the plurality of ceramic lenses has a smaller distance d than the other ceramic lenses. If the condition 13) is satisfied, the other ceramic lenses also satisfy the conditional expression (13). Therefore, the positional relationship between the ceramic lens 2 closest to the CCD element 3 and the CCD element 3 is defined, and the movable range of the ceramic lens 2 is limited to the movable range satisfying the conditional expression (13), as described above. The effect of can be obtained.

  In any of the above cases, as shown in FIG. 4, there may be a configuration in which the photographing lens 5 other than the ceramic lens is interposed between the ceramic lens 2 and the CCD element 3. In this case, in the calculation of the conditional expression (13), the influence can be avoided by calculating the distance d by converting the photographing lens 5 other than the ceramic lens into air.

  In the above embodiments and modifications, the case where the image pickup device 3 is a CCD device has been described. However, any other device can be used as long as an image is picked up by forming incident light on the image plane with a photographing lens. An image sensor can also be used.

It is an external appearance perspective view of the digital still camera of this embodiment. It is a schematic diagram which shows the structure of the lens unit of this embodiment. It is a schematic diagram explaining the area | region through which the light of a ceramic lens passes. It is a schematic diagram explaining the state in which another imaging lens intervenes between a ceramic lens and a CCD element.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Lens unit 2 Ceramic lens 3 CCD element 31 Image surface 4 Void 5 Shooting lens other than ceramic lens d Distance from image surface to lens surface F F value of ceramic lens r Radius of void

Claims (5)

In a lens unit comprising a photographic lens and an image sensor,
The taking lens is a ceramic lens;
When the distance from the image plane of the image sensor to the lens surface of the ceramic lens is d, the radius of the void in the ceramic lens is r, and the F value of the ceramic lens is F, the distance d is the following conditional expression: (1) The lens unit characterized by satisfy | filling.

In a lens unit including a plurality of photographing lenses and an image sensor,
The plurality of photographing lenses include ceramic lenses,
When the distance from the image plane of the image sensor to the lens surface of the ceramic lens is d, the radius of the void in the ceramic lens is r, and the F value of the ceramic lens is F, the distance d is the following conditional expression: (2) The lens unit characterized by satisfy | filling.

In a lens unit including a plurality of photographing lenses and an image sensor,
The plurality of photographic lenses include a plurality of ceramic lenses,
Among the plurality of ceramic lenses, for a ceramic lens closest to the image sensor, d is a distance from the image surface of the image sensor to the lens surface, r is a radius of a void in the ceramic lens, and an F value of the ceramic lens. Is a lens unit, wherein the distance d satisfies the following conditional expression (3).

  4. The lens unit according to claim 2, wherein the distance d is calculated by air-converting a photographic lens other than the ceramic lens existing between the ceramic lens and the imaging element. 5.   The lens unit according to any one of claims 1 to 4, wherein the ceramic lens is formed by processing translucent ceramics into a lens shape.

Images