JPH04249227A - Optical device - Google Patents

Abstract

PURPOSE:To obtain an optical device by which an excellent image is obtained by properly setting the optical arrangement of a primary focusing surface by a photographing lens with a field lens in the optical device provided with a secondary image formation system. CONSTITUTION:In the case that an object image formed on the primary focusing surface by the photographing lens 11 is reformed on a specified surface by a secondary image formation lens 33 through the field lens 31 after changing image formation magnification, the field lens 31 is provided with plural lenses and arranged so that the primary focusing surface may be positioned in the plural lenses which constitute the field lens 31.

Description

[Detailed description of the invention]

0001

[Field of Industrial Application] The present invention relates to an optical device, and more particularly, an object image formed on a primary focus plane by a photographing lens is transferred to a CCD or the like by a secondary imaging lens via a field lens (also called a condenser lens). The present invention relates to an optical device having a so-called secondary imaging system that re-forms an image on the surface of an image sensor by changing the imaging magnification.

0002

[Background Art] In recent years, electronic still cameras (SV cameras) have been developed to record still images taken using solid-state image sensors such as CCDs on magnetic disks, and images taken using image sensors are recorded on magnetic tapes. Optical devices such as video cameras are often used.

[0003] Among these optical devices, there is one in which an imaging means of a predetermined size is arranged on the primary focus plane (imaging plane) of a photographing lens. In this optical device, even if the optical device is of an interchangeable lens type, each has its own photographing system due to differences in the effective surface size of the imaging means and the flange back of the photographing lens, and there is no compatibility between the photographing lenses. For this reason, optical devices that match the dimensions of the image pickup device have been used.

On the other hand, Japanese Patent Laid-Open No. 63-168637 uses the mechanisms of a 35 mm film camera, such as the photographing lens, shutter, and quick return mirror, as is.
Remove the back cover of the camera body and install the secondary imaging system that has a field lens (condenser lens), relay imaging lens, etc. and the imaging means on the focal plane (secondary focal plane) of the secondary imaging system. We have proposed an optical device that is removably equipped with a so-called SV bag.

[0005] With this, a taking lens for 35 mm film is used as is, and an object image formed on a primary focus plane by the taking lens is re-imaged on an image pickup device such as a CCD using a secondary imaging system. When the dimensions of the image sensor are changed, this can be done simply by changing the magnification of the secondary imaging system.

Generally, optical devices using a secondary imaging system have the following advantages. (b) Even if the effective surface size of the image sensor changes from 2/3 inch to 1/2 inch to 1/3 inch, it can be accommodated by changing the magnification of the secondary imaging system, and the camera body Basic imaging mechanisms such as quick return mechanism and shutter mechanism can be used as is. (b) Multi-plate imaging devices can be accommodated by simply changing the secondary imaging system, and the basic imaging mechanism of the camera body can be used as is, similar to (b).

[0007]

[Problems to be Solved by the Invention] Generally, optical devices using a secondary imaging system have the above-mentioned features, but on the other hand, they have the following advantages compared to optical devices in which an image sensor is placed directly on the primary focal plane. There are some problems. (c) When a secondary imaging system is used, the number of optical systems increases, which causes many aberrations and deteriorates optical performance. (d) Since the optical length of the secondary imaging system (the length from the primary focusing surface to the secondary focusing surface) is added, the entire optical device becomes larger and it becomes difficult to make the camera thinner. (e) When a mechanical shutter mechanism is placed immediately before the subject side of the primary focus plane, the position of the field lens on the optical axis comes to be located immediately behind the primary focus plane. For this reason, dirt, dust, etc. adhering to the field lens surface form an image on the image sensor surface, appear as black spots on the image surface, and become a cause of deterioration in image quality.

In particular, with the recent miniaturization (higher resolution) of image pickup devices, the permissible size of dirt and dust on the field lens surface that does not adversely affect the image is becoming smaller and smaller. Dust is a major problem.

The present invention utilizes a secondary imaging system to achieve an optical device having the above-mentioned features, and the object image (primary focal plane) formed by the photographing lens and the field lens (
By appropriately configuring the optical arrangement with the condenser lens (condenser lens) and the mechanisms in its vicinity, we prevent dirt and dust from adhering to the field lens, and even if it does, we ensure that the image quality is not adversely affected as much as possible. An object of the present invention is to provide an optical device that can obtain good images.

0010

[Means for Solving the Problems] The optical device of the present invention changes the imaging magnification of an object image formed by a photographing lens on a primary focus plane via a field lens and by a secondary imaging lens onto a predetermined plane. When re-imaging the field lens, the field lens has a plurality of lenses, and is characterized in that it is arranged so that the primary focal plane is located among the plurality of lenses constituting the field lens.

In particular, in the present invention, the primary focus surface is located approximately at the center on the optical axis of the plurality of lenses constituting the field lens, and the object-side lens surface of the field lens is It is characterized in that it is closed by a shutter means for controlling the amount of light, and the lens surface on the image side is closed by the secondary imaging lens and its holding member.

0012

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a schematic diagram of a main part of an embodiment of the present invention. In the figure, reference numeral 1 denotes an exchangeable photographic lens barrel for 35 mm film, which holds a photographic lens 11. 4 is S
This is a camera body for a V camera. A photographic lens barrel 1 is removably attached to a camera body 4 via a photographic lens mount 12 and a camera mount 21. 5 is a back cover, which is fitted onto the camera body 4. 23 is a click return mirror, which has a fulcrum 23b as shown by an arrow 23a.
It is rotatable around , and guides the light beam from the photographing lens 11 to the finder system.

Reference numeral 24 denotes a shutter means, which controls the amount of passing light. Reference numeral 22 denotes a front plate, which functions as a holding frame for various mechanisms on the camera body side. 25 is a primary focus plane, on which an object image formed by the photographing lens 11 is formed. 31 is a field lens (also called a condenser lens), which has a plurality of lenses. The figure shows a case where the lens is composed of two lenses 31a and 31b. The primary focus plane 25 is set to be located between the lens 31a and the lens 31b of the field lens 31.

The field lens 31 has a primary focus plane 25
A light beam based on the object image formed in the image forming apparatus 1 is guided toward a secondary imaging lens 33, which will be described later. A holding member 32 holds the field lens 31. The object side lens surface of the field lens 31 is shielded from the outside air by the holding member 32, the front plate 22, and the shutter means 24. 33
is a secondary imaging lens, which reduces the object image formed on the primary focus plane 25 onto the surface of an imaging device 39 consisting of a CCD or the like via an optical low-pass filter 38 according to the effective screen of the imaging device 39. Or the image is enlarged. The field lens 31 and the secondary imaging lens 33 constitute one element of the secondary imaging system.

34 is a holding frame, and the secondary imaging lens 33
is held. 40 is a holding member, and the image sensor 39
, and is attached to the holding frame 34. 35 is a connecting member, which is cylindrical and connects the front plate 22 and the holding frame 3.
4 are fitted and connected through fitting portions 35a and 35b. The lens surface on the image plane side of the field lens 31 includes a holding member 32, a connecting member 35, a holding member 34, and a secondary imaging lens 33.
It is closed off from the outside air. A biasing spring 36 biases the front plate 22 and the connecting member 35 in a direction toward each other. Reference numeral 37 denotes an adjustment screw that moves the secondary imaging lens 33 (coupling member 35 and holding frame 34) in the optical axis direction to adjust the focus.

Reference numeral 61 indicates a primary focus plane of the finder system. 62 is a field lens, and the primary focus plane 61
The object image formed is guided to an erector lens 64 via a mirror 63. The erector lens 64 re-images the object image formed on the primary focus surface 61 onto a secondary focus surface 65. 66 is an eyepiece lens, and the secondary focus plane 6
The object image formed at 5 is observed from an eye point 67.

In this embodiment, the space on the object side and the space on the image side of the field lens 31 are sealed off from the outside air as described above, thereby preventing dirt and dust from adhering to the lens surface of the field lens 31. are doing. The shutter means 24 opens and closes, but in the case of an electronic still camera, the maximum shutter time is about 1/8 to 1/15 seconds, which is a short time, so the inflow of dirt and dust is extremely small, which poses a problem. There isn't.

Further, in this embodiment, the object-side and image-side lens surfaces of the field lens 31 are set to be far away from the primary focal plane 25. As a result, even if dust or dirt adheres to the lens surface, the image will be blurred on the surface of the image sensor 39, thereby preventing deterioration in image quality.

Next, in this embodiment, when the size corresponding to one pixel of the image sensor 39 on the secondary focus plane appears as a black dot, the required distance L (mm) from the primary focus plane 25 is determined. A light-blocking area (area formed by dirt, dust, etc.) will be explained using FIG. 2.

In FIG. 2, a circular image of radius ya (such as dust or It is also assumed that a circular image with a radius yb is formed at a position (corresponding to the image sensor surface) a distance b away from the lens 201 on the image plane side (right side).

At this time, the condition for image Pb to become a black spot is that the portion corresponding to image Pa is shielded from light. It is located a distance L to the left from the image Pa and has a radius of x1
This is nothing more than blocking out that part. In that case, the following formula holds true through simple geometric calculations. For example, a=80(mm), b=40(mm)L=
3 (mm), yb = 5 × 10-3 (mm
) D=15 (mm) becomes.

Therefore, in this case, the primary focus plane is the image Pa
However, assuming that images Pb are respectively formed on the secondary focus plane, in order to block light from a circle with a radius of 5 μm on the secondary focus plane, a radius of 291 μm is required at a position 3 mm away from the primary focus plane. All you have to do is block out the light within the circle.

Similarly, the radius x2 to be shielded from light at a position a distance L to the right from the image Pa is determined by equations (1) and (2), where the size of one pixel of the image sensor is approximately several μm to more than ten μm. It is from.

Therefore, x1 ≒ x2 ≒ LD/(2a), and the light shielding area necessary to shield the image Pa is proportional to L.

In other words, it is shown that as the distance between the primary focus plane and the field lens surface increases, the influence of dirt, dust, etc. attached to the field lens surface appearing as black spots on the image can be reduced.

Therefore, in this embodiment, as described above, the primary focal plane 25 is located between the two lenses 31a and 31b constituting the field lens 31, so that the object side of the field lens 31 is separated from the primary focal plane. The distance to the lens surface or the lens surface on the image plane side is made to be as large as possible.

As a result, even if dirt or dust adheres to the object-side or image-side lens surface of the field lens 31, it is displayed as a blurred image on the image pickup device 39, thereby preventing the image from appearing as a black spot. .

[0028]

According to the present invention, when constructing a secondary imaging system, by setting the optical arrangement of the primary focus plane of the photographing lens and the field lens as described above, dust can be removed from the field lens surface. Even if dirt or dust is attached, it is possible to effectively prevent black spots from appearing on images, thereby achieving an optical device that can obtain good images.

[0029] Furthermore, by shielding the field lens surface to which dirt and dust may adhere from the outside air as described above, the adhesion of dirt and dust is effectively prevented. .

As described above, according to the present invention, by appropriately setting the magnification of the secondary imaging system, it is possible to attach an exchangeable photographic lens for 35 mm film to the SV camera body and use it as an SV camera. Optical devices can be achieved.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram of main parts of an embodiment of the present invention.

FIG. 2 is an explanatory diagram showing the relationship between the size of an image near the primary focus plane and an image on the secondary focus plane in the optical device of the present invention.

[Explanation of symbols]

1 Photographic lens barrel 4 Camera body 5 Back cover
11 Photographic lens 24 Shutter means
25 Primary focus plane 31 Field lens
33 Secondary imaging lens 39 Image sensor

Claims (4)

[Claims] Claim 1: When an object image formed on a primary focus plane by a photographic lens is re-imaged on a predetermined plane by changing the imaging magnification by a secondary imaging lens via a field lens, the field lens 1. An optical device comprising a plurality of lenses arranged such that the primary focal plane is located among the plurality of lenses constituting the field lens. 2. The optical device according to claim 1, wherein the primary focus plane is located approximately at the center on the optical axis of a plurality of lenses constituting the field lens. 3. A lens surface on the object side of the field lens is shielded by a shutter means for controlling the amount of passing light, and a lens surface on the image surface side is shielded by the secondary imaging lens and its holding member. The optical device according to claim 1, characterized in that: 4. The optical device according to claim 1, wherein the photographing lens is of a detachable interchangeable lens type.