JP2006003572A - Photographing optical system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a photographic optical system less likely to cause flare spots which causes image quality to deteriorate. <P>SOLUTION: The photographic optical system has 1st to 5th lenses 11 to 15 for forming a subject image and arranged along in the optical axis Ax direction, an aperture stop 2 for adjusting the F value, and a reflected light stop 3, constituted so that its aperture is consecutively changed interlocked with the aperture stop 2 and restraining flare spots from being generated, by converging the light reflected on an image formation surface 100. The reflected light stop 3 is installed nearer to the image side than to the the aperture stop 2. The reflected light stop 3 is interlocked with the aperture stop 2 so that its aperture is as small as possible, in a range where effective luminous flux passing through the aperture stop 2 is not intercepted. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a photographing optical system.

  A digital camera that converts a subject image formed through a photographing lens into an electrical signal by an image sensor and records a photographed image as digital data is widely used.

  The digital camera has a problem that a flare spot that deteriorates the image quality is likely to occur compared to the silver salt camera. A flare spot is a ghost that is reflected on the imaging surface and incident on the imaging lens, and the reflected light is further reflected on the lens surface (rear surface or front surface) to be generated at the center of the imaging surface. . The reason why the flare spot is likely to occur in the digital camera is considered to be because the reflectance of the surface of the image pickup device arranged on the imaging surface is higher than the reflectance of the silver salt film.

JP 7-294814 A

  An object of the present invention is to provide a photographing optical system in which a flare spot that degrades image quality is unlikely to occur.

Such an object is achieved by the present inventions (1) to (4) below.
(1) a plurality of lenses arranged along the optical axis direction for forming a subject image;
An aperture stop to adjust the F value;
The aperture is configured to continuously change in conjunction with the aperture stop, and has a reflected light stop that suppresses the generation of flare spots by restricting the light reflected on the imaging surface,
The photographing optical system according to claim 1, wherein the reflected light stop is disposed on the image side of the aperture stop.

  Thereby, even when the aperture stop is on the small stop side, it is possible to reliably prevent the occurrence of a flare spot that degrades the image quality.

  (2) The photographing optical system according to (1), wherein the reflected light stop is installed between a lens that causes a flare spot and the imaging plane.

  Thereby, since the reflection area of the harmful light beam on the rear surface of the lens that causes the flare spot can be reduced, it is possible to reliably prevent the occurrence of the flare spot that deteriorates the image quality.

  (3) The photographing optical system according to (1) or (2), wherein the reflected light diaphragm is installed immediately after a lens that causes a flare spot.

  Thereby, since the ratio of the harmful light beam (reflected light) to the effective light beam can be further reduced, it is possible to more reliably prevent the occurrence of a flare spot that degrades the image quality.

  (4) The reflected light diaphragm is coupled with the aperture stop so that the aperture is as small as possible within a range in which the effective light beam that has passed through the aperture stop is not shielded. Any one of the photographing optical systems.

  Accordingly, it is possible to more reliably prevent the occurrence of a flare spot that degrades the image quality without darkening the subject image or causing vignetting.

  According to the present invention, it is possible to reliably prevent the occurrence of a flare spot that degrades the image quality even when the aperture stop is on the small stop side.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a photographing optical system of the present invention will be described in detail based on preferred embodiments shown in the accompanying drawings.
FIG. 1 is a half vertical sectional view showing an embodiment of the photographing optical system of the present invention. In the following description, the left side in FIG. 1 is referred to as “object side” or “front”, and the right side is referred to as “image side” or “rear”.

  A photographing optical system 1 shown in FIG. 1 is a photographing lens for a digital camera, and in order from the object side, a concave meniscus first lens 11 having a convex surface facing the object side and a concave meniscus having a convex surface facing the object side. A second lens 12, a concave meniscus third lens 13 having a convex surface facing the image side, a concave meniscus fourth lens 14 having a convex surface facing the object side, and a biconvex fifth lens 15. Yes.

  These first lens 11 to fifth lens 15 are held by a lens holder 4 formed by combining a plurality of cylindrical members.

  A subject image is formed on the image plane 100 by the first lens 11 to the fifth lens 15. For example, a light receiving surface of an image sensor such as a CCD image sensor or a CMOS image sensor is disposed on the image plane 100, and the image sensor converts a subject image into an electrical signal.

  Each of the first lens 11 to the fifth lens 15 may be a single lens or may be formed by bonding a plurality of lenses.

  Between the second lens 12 and the third lens 13, an aperture stop 2 for adjusting the F value of the photographing optical system 1 is installed. The aperture stop 2 is a so-called iris diaphragm that can continuously change the diameter of a circular or polygonal hole surrounded by a plurality of thin plate-like blades arranged in an annular shape.

  A diaphragm drive lever 5 installed substantially parallel to the optical axis Ax is connected to the outer peripheral portion of the drive ring 21 of the aperture stop 2. When the aperture drive lever 5 is rotated about the optical axis Ax, the aperture of the aperture stop 2 can be changed by rotating the drive ring 21 accordingly.

  Between the fourth lens 14 and the fifth lens 15, a reflected light stop 3 is provided to stop the harmful light beam reflected by the imaging plane 100. In other words, the reflected light stop 3 is disposed on the image side of the aperture stop 2 via the third lens 13 and the fourth lens 14. Similar to the aperture stop 2, the reflected light stop 3 is composed of an iris stop that can continuously change its aperture.

  The drive ring 31 of the reflected light diaphragm 3 is connected to the diaphragm drive lever 5 described above. Therefore, when the aperture driving lever 5 is rotated about the optical axis Ax, the aperture of the reflected light aperture 3 changes in conjunction with the change of the aperture of the aperture stop 2.

  As will be described later, the reflected light stop 3 is configured to be interlocked with the aperture stop 2 so that its aperture is as small as possible within a range in which the effective light beam that has passed through the aperture stop 2 is not shielded. . Therefore, the subject image is not darkened or vignetted due to the reflected light stop 3.

  2 and 3 are diagrams for explaining how much the aperture of the reflected light aperture 3 can be reduced within a range in which the effective light beam is not shielded. FIG. 2 shows the aperture aperture 2 when the aperture is maximized. FIG. 3 shows the minimum stop when the aperture stop 2 has the smallest aperture. In FIGS. 2 and 3, for the sake of simplification, the refraction of light rays other than the rear surface of the fifth lens 15 is omitted.

When the aperture stop 2 is opened, as shown in FIG. 2, the effective light flux F ₁ reaching the outermost peripheral portion of the image plane 100 has a width as shown in the figure, so that the reflected light stop 3 reduces the effective light flux F ₁ . In order not to block, the aperture of the reflected light aperture 3 can be reduced to the dimension a in FIG. Therefore, when the aperture stop 2 is opened, the aperture of the reflected light stop 3 is substantially a.

When the aperture stop 2 is at the minimum stop, as shown in FIG. 3, the effective light beam F ₂ reaching the outermost peripheral portion of the image plane 100 has a width as shown in the figure, so that the reflected light stop 3 is effective light beam F _2. In order not to block the aperture, the aperture of the reflected light aperture 3 can be reduced to a dimension b in FIG. Therefore, when the aperture stop 2 is at the minimum stop, the aperture of the reflected light stop 3 is approximately b.

  In addition, when the aperture stop 2 is narrowed from the open state to the minimum stop state, the aperture of the reflected light stop 3 gradually decreases from a to b. The aperture is interlocked with the aperture stop 2 via the aperture drive lever 5 so that the aperture does not block light.

  In general, a digital camera has a problem that a flare spot that degrades image quality is likely to occur compared to a silver salt camera. The reason why the flare spot is likely to occur in the digital camera is considered to be because the reflectance of the surface of the image pickup device arranged on the imaging surface 100 is higher than the reflectance of the silver salt film. Hereinafter, the flare spot will be described with reference to FIG.

  The imaging optical system 200 of the comparative example shown in FIG. 5 corresponds to the imaging optical system 1 of the present invention in which the reflected light stop 3 is removed.

  The flare spot is a ghost that is generated when light incident on the imaging optical system is reflected by the imaging surface, and the reflected light is further reflected by the rear surface of the lens and collected at the center of the imaging surface. As shown in FIG. 5, in the photographing optical system 200, the fourth lens 14 is a lens that causes a flare spot, and the light reflected by the imaging plane 100 is indicated by a two-dot chain line in FIG. 5. Then, the light is further reflected by the concave surface on the rear surface of the fourth lens 14 to generate a flare spot at the center of the image plane 100. In the photographing optical system 200 of the comparative example, the light reflected in substantially the entire range (the range indicated by the symbol c) on the rear surface of the fourth lens 14 reaches the center of the image plane 100.

  Such a flare spot is not noticeable on the open side of the aperture stop 2 and does not cause a problem. However, the flare spot is noticeable on the small stop side of the aperture stop 2 and causes a problem. This is presumably because the ratio of the harmful light beam (reflected light) to the effective light beam becomes large on the small aperture side.

  On the other hand, the photographic optical system 1 of the present invention can suppress the occurrence of flare spots even on the small stop side of the aperture stop 2 by providing the reflected light stop 3, and the flare spot becomes a problem. Can be prevented. The reason for this will be described with reference to FIG.

  As described above, the aperture of the reflected light diaphragm 3 is made as small as possible within a range in which the effective light beam is not blocked. In the minimum stop state of the aperture stop 2 shown in FIG. It has been narrowed down. Thereby, the light reflected by the imaging surface 100 is stopped by the reflected light stop 3 before reaching the rear surface of the fourth lens 14, and the amount of light reaching the rear surface of the fourth lens 14 is reduced. Only the light reflected in a part of the range near the center of 14 (the range indicated by reference sign d) reaches the center of the image plane 100. Since the range d is significantly smaller than the range c in FIG. 5, the photographic optical system 1 can reduce the degree of flare spot as compared with the photographic optical system 200. In practice, the flare spot is a problem. Can be prevented.

  The reflected light stop 3 may be installed on the image side of the aperture stop 2 and between the imaging plane 100 and the lens (fourth lens 14 in the present embodiment) that causes a flare spot. As in the embodiment, it is more preferable to install the lens immediately after the lens causing the flare spot. Thereby, the ratio of the harmful light beam (reflected light) can be further reduced while the effective light beam is not shielded, and the flare spot can be prevented more reliably.

  Although the aperture of the reflected light diaphragm 3 is increased on the open side of the aperture stop 2, the flare spot is not conspicuous on the open side of the aperture stop 2 as described above, so that there is no problem.

  In FIGS. 4 and 5, in order to simplify the drawing, the refraction of the light beam by the lens is omitted.

  As described above, the photographic optical system of the present invention has been described with respect to the illustrated embodiment. However, the present invention is not limited to this, and each part constituting the photographic optical system can have any configuration that can exhibit the same function. Can be substituted. Moreover, arbitrary components may be added.

It is a semi-longitudinal sectional view showing an embodiment of a photographing optical system of the present invention. It is a figure for demonstrating how much the aperture of a reflected light aperture can be made small in the range which does not shield an effective light beam (at the time of opening of an aperture stop). It is a figure for demonstrating how much the aperture of a reflected light aperture can be made in the range which does not shield an effective light beam (at the time of minimum aperture stop aperture stop). It is a figure for demonstrating the range which a harmful light beam reflects in the rear surface of a lens in the imaging optical system of this invention. It is for demonstrating the range which a harmful light beam reflects in the rear surface of a lens in the imaging optical system of a comparative example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Shooting optical system 2 Aperture stop 21 Drive ring 3 Reflected light stop 4 Lens holder 5 Aperture drive lever 11 1st lens 12 2nd lens 13 3rd lens 14 4th lens 15 5th lens 100 Imaging surface 200 Imaging optical system Ax Optical axis F ₁ , F ₂ Effective luminous flux

Claims (4)

A plurality of lenses arranged along the optical axis direction to form a subject image;
An aperture stop to adjust the F value;
The aperture is configured to continuously change in conjunction with the aperture stop, and has a reflected light stop that suppresses the generation of flare spots by restricting the light reflected on the imaging surface,
The photographing optical system according to claim 1, wherein the reflected light stop is disposed on the image side of the aperture stop.   The photographic optical system according to claim 1, wherein the reflected light stop is disposed between a lens that causes a flare spot and the imaging plane.   The photographing optical system according to claim 1, wherein the reflected light stop is installed immediately after a lens that causes a flare spot.   The photographing according to any one of claims 1 to 3, wherein the aperture of the reflected light is interlocked with the aperture stop so that the aperture becomes as small as possible within a range in which the effective light beam that has passed through the aperture stop is not shielded. Optical system.

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