JPH0915477A - Lens barrel for soft focus lens - Google Patents

Abstract

PURPOSE: To provide an inexpensive lens barrel for a soft focus lens which is easily and very simply focused. CONSTITUTION: This lens barrel is provided with an external barrel 4 attached to a camera having a focus detector, an intermediate barrel 5 arranged coaxially with the barrel 4, and an internal barrel 6 which is arranged coaxially with the barrel 5 and to which the soft focus lens 1 is attached; and the barrels 5 and 6 are arranged to be integrally moved along an optical axis with respect to the barrel 4, and the barrel 6 is arranged to be moved along the optical axis with respect to the barrel 5. Then, the maximum moving amount between the barrels 5 and 6 is set to be nearly equal to a distance between the position of the lens 1 where it is regarded as in focus by the focus detector of the camera for a subject being at a specified distance and the position of the lens 1 where the highest resolution is obtained for the subject.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a lens barrel for a camera, and more particularly to a lens barrel for a soft focus lens.

[0002]

2. Description of the Related Art A soft-focus lens is a lens in which spherical aberration is intentionally generated or left, and since it creates a fantastic depiction of the flare due to spherical aberration on the contour of the subject, it is especially useful for female portraits. Widely used for photography. This type of soft focus lens is roughly classified into the following two types in terms of function. One is to change the spherical aberration by moving a specific (two or more) lens group while keeping the focus position constant. From the normal sharp mode in which spherical aberration is corrected, the spherical aberration remains. This is a lens in which the amount of spherical aberration, that is, the amount of software, can be continuously changed up to the soft mode. Of course, the amount of spherical aberration also changes depending on the diameter of the aperture stop, so in practice, the amount of software is set by two factors: lens movement and aperture setting. The other is that after the lens is moved and focused, the lens is fixed and the soft amount is controlled only by the diaphragm.

[0003]

By the way, the biggest problem in using a soft focus lens is focusing. The soft focus lens is often used by being attached to a camera, such as a single-lens reflex camera, which can confirm the focus state on the screen for the purpose of checking the soft amount. However, the soft focus lens has a low image contrast on the focus surface where the resolution is highest, which is considered to be the best focus in actual shooting, and no resolution appears at the high contrast position where it is easy to determine the best focus on the screen. However, the work of focusing on the screen requires considerable skill.

In order to reduce the difficulty of focusing, two methods have been proposed. One is an operation member for changing the spherical aberration amount after performing the focusing by using the soft focus lens whose spherical aberration amount is changed by the movement of the lens group described above, in a state where the spherical aberration is corrected. Is operated to generate a predetermined spherical aberration, and an image is taken. According to this method, focusing can be performed as a sharp lens, so that focusing can be performed easily and with high accuracy. However, in order to change the spherical aberration while keeping the image surface constant, at least two lens groups must be moved non-linearly, which requires a complicated optical system and a complicated lens barrel structure. It was very disadvantageous.

The second method is autofocusing, in which an electric focus detecting device is built in the camera body, the signal from the focus detecting device is calculated, and the lens is driven by a lens driving device such as a motor from the calculation result. Is to move and focus. With this method, focusing is done mechanically, so stable focus can always be obtained regardless of the photographer's skill level, and the processing speed of the microcomputer and the performance of the motor improve the shooting efficiency. Has begun to give satisfactory results. However, this method also requires a memory in which the lens specific information for determining the best focus position is written from the signals of the lens driving device and the focus detection device for moving the lens, and as a result, it is expensive. It had to be a lens.

The present invention has been made in view of the above problems, and it is an object of the present invention to provide a lens barrel for a soft focus lens which is easy to focus, simple and low cost.

[0007]

The present invention utilizes a phase difference detection type focus detection device generally used in an autofocus camera, or a split image prism arranged on a finder screen,
It is intended to provide a means for accurately focusing a soft focus lens. FIG. 2 is a diagram schematically showing the image formation of the soft focus lens 1. The two types of focus detection methods each detect a position where a part of the light flux passing through the taking lens, generally a light flux a having an F number of about 4 to 6 intersects with the optical axis, and defines it as a focus position P. It's something to see. However, in the soft focus lens 1, the best focus position in practical use, that is, the focus position Q at which the highest resolution is obtained, as shown in FIG. 2, is almost coincident with the Gaussian image plane, and the focus position by the focus detection device is the same. It is very different from P. Therefore, if the above focusing method is used as it is, good focusing cannot be achieved.

However, when the soft focus lens 1 is used for photographing, it is customary that the subject distance is within a certain range, so that the spherical aberration amount can be regarded as constant within that range, and therefore the maximum value is obtained. The distance A between the focus position Q at which the resolution is obtained and the focus position P by the focus detection device can also be regarded as constant.

The present invention focuses on this point, that is, an outer cylinder attached to a camera having a focus detection device, an intermediate cylinder arranged coaxially with the outer cylinder, and an intermediate cylinder arranged coaxially with the intermediate cylinder. It has an inner cylinder to which a soft focus lens is attached, and an intermediate cylinder and an inner cylinder are arranged to be movable integrally with the outer cylinder along the optical axis, and the inner cylinder is arranged along the optical axis with respect to the intermediate cylinder. The position P of the soft focus lens, which is arranged movably, and in which the maximum amount of movement between the intermediate cylinder and the inner cylinder is regarded as the focus by the focus detection device of the camera with respect to the subject at a predetermined distance, and the subject The lens barrel for a soft focus lens is characterized in that the distance A between the position A and the position Q of the soft focus lens that provides the highest resolution is set to be substantially equal.

[0010]

The intermediate cylinder and the inner cylinder are united together along the optical axis so that the inner cylinder is moved to the one end side with respect to the intermediate cylinder in advance, and then the lens focus position is regarded as the focus by the camera. Moving. Then, the inner cylinder is moved to the other end side with respect to the intermediate cylinder. As a result, the photographer can move the lens from the focus position P by the focus detection device to the focus position Q at which the highest resolution can be obtained quickly and accurately, so that the photographer can always shoot at the best focus position Q. Becomes

[0011]

FIG. 1 shows an embodiment of a lens barrel for a soft focus lens according to the present invention. The lens barrel of this embodiment is a bayonet mount 3 for mounting on a camera.
The outer cylinder 4 is fixed to the front end of the bayonet mount 3, that is, the left end in the drawing with screws. A cam barrel 5 is arranged on the inner surface of the outer barrel 4 coaxially with the outer barrel 4, and a spiral cam groove 5a is formed in the cam barrel 5. The cam pin 4 protruding inward from the inner surface of the outer cylinder 4 is inserted into the cam groove 5a.
a is engaged, and when the cam barrel 5 is rotated in this manner, the cam barrel 5 moves along the optical axis.
The action of the cam pin 4a and the cam groove 5a may be replaced by a helicoid, or may be one using two helicoids or one using two cam barrels.

A lens barrel 6 is arranged on the inner surface of the cam barrel 5 coaxially with the cam barrel 5, and a stepped portion 6a is provided on the outer face of the lens barrel 6. A limiting ring 8 is screwed to the rear end portion of the lens barrel 6, that is, the right end portion in the drawing, and the cam barrel 5 is externally fitted between the stepped portion 6a of the lens barrel and the limiting ring 8. The distance between the stepped portion 6a and the limiting ring 8 is set to the cam cylinder 5
Is formed to be slightly longer than the axial length of the lens barrel 6, so that the cam barrel 5 has a play A in the axial direction.
Is fitted outside. A groove (not shown) is provided in the lens barrel 6 in the axial direction, and a pin (not shown) protruding inward from the inner surface of the cam barrel 5 is engaged with the groove. In this way, the lens barrel 6 cannot rotate with respect to the cam barrel 5, but is configured to be movable by the play A in the axial direction. In order to prevent the cam barrel 5 and the lens barrel 6 from rotating relative to each other, an axial groove is provided on the cam barrel 5 side.
It is also possible to provide a pin on the outer surface of the lens barrel 6.

A group of two soft focus lenses 1 are fixed to the inner surface of the lens barrel 6, and a large-diameter focus ring 7 is attached to the front end of the lens barrel 6 via a fixed diaphragm 2.
Is screwed. Thus, the cam cylinder 5 forms an intermediate cylinder, and the lens cylinder 6 and the focus ring 7 form an inner cylinder. Further, when adjusting the soft amount, the focus ring 7 can be removed and replaced with a fixed diaphragm having a different diameter. A rubber rubber is attached to the outer surface of the focus ring 7 to facilitate the focusing operation. However, knurling may be applied instead of rubber.

As described above, in this embodiment, when the lens barrel 6 is rotated by the focus ring 7, the cam barrel 5 is also rotated accordingly, and the cam barrel 5 moves in the optical axis direction along the cam groove 5a. Therefore, along with this, the lens barrel 6 also moves in the optical axis direction, and therefore the soft focus lens 1 moves in the optical axis direction. In addition to this main focusing operation, the soft focus lens 1 can be moved in the direction of the optical axis by the play A as a supplement by pushing or pulling out the lens barrel 6 by the focus ring 7.

A play A in the axial direction between the cam barrel 5 and the lens barrel 6 is determined as follows. That is, the focus detection device built into the camera body to which this lens barrel is to be attached is investigated to know the width of the light beam a used for focus detection. Next, the soft focus lens 1 with the above-mentioned luminous flux width at a typical subject distance
The spherical aberration amount of is calculated. Since the best focus position Q in soft focus substantially coincides with the Gaussian image plane, the spherical aberration amount is the distance A between the focus position P by the focus detection device and the best focus position Q. Cam barrel 5
The play A in the axial direction between the lens barrel 6 and the lens barrel 6 is formed to be equal to the distance A between the focus positions. The distance A between the focus positions may be experimentally obtained.

Next, an actual method of using this lens barrel will be described. In the following description, the case where the spherical aberration of the soft focus lens 1 is undercorrected will be described. First, this lens barrel is attached to the camera, and the focus ring 7 is pushed in the mounting direction. By this operation, the stepped portion 6a of the lens barrel 6 contacts the cam barrel 5. Then, the focus detection device built into the camera is used to rotate the focus ring 7 to manually focus.
When the in-focus sign of the focus detection device appears, the rotation of the focus ring 7 is stopped, and the focus ring 7 is pulled out toward the subject side while taking care not to rotate the focus ring 7, and the shutter is released. By pulling out the focus ring 7 as much as possible,
Focus position P and best focus position Q by the focus detection device
The lens 1 moves by the distance A between and, and thus, the image can be taken at the best focus position Q.

As described above, according to this embodiment, since the focus detection device built into the camera is used as it is for determining the focus position, no matter how skilled or inexperienced the beginner is, compared to focusing with the screen. Even then, stable focus accuracy can be obtained. Furthermore, since the focusing operation can be performed only by operating the focus ring 7, it is possible to perform quick shooting. It should be noted that in the above embodiment, the case where the spherical aberration of the soft focus lens 1 is undercorrected has been described.
Then, the focus ring 7 is fully pulled out to the subject side, focusing is then performed using the focus detection device incorporated in the camera, and finally the focus ring 7 is pushed in the mounting direction.

[0018]

As described above, according to the present invention, it is possible to obtain a lens barrel for a soft focus lens that is easy to focus, is very simple, and is low in cost.

[Brief description of the drawings]

FIG. 1 is a partial sectional front view showing an embodiment of a lens barrel for a soft focus lens according to the present invention.

FIG. 2 is a schematic diagram showing the principle of the present invention.

[Explanation of symbols]

1 ... Soft Focus Lens 2 ... Fixed Aperture 3 ... Bayonet Mount 4 ... Outer Cylinder 4a ... Cam Pin 5 ... Cam Cylinder 5a ... Cam Groove 6 ... Lens Cylinder 6a ... Stepped Part 7 ... Focus Ring 8 ... Limit Ring a ... Focus Detection Device Luminous flux used by P ... Focus position by focus detection device Q ... Best focus position A ... Play

Claims (1)

[Claims] 1. An outer cylinder attached to a camera having a focus detection device, an intermediate cylinder arranged coaxially with the outer cylinder, and an inner cylinder arranged coaxially with the intermediate cylinder to which a soft focus lens is attached. The intermediate cylinder and the inner cylinder are arranged so as to be movable integrally with the outer cylinder along the optical axis, and the inner cylinder is arranged so as to be movable with respect to the intermediate cylinder along the optical axis. The maximum amount of movement between the barrel and the inner barrel is the position of the soft focus lens at which the focus detection device of the camera regards the subject at a predetermined distance as the focus, and the highest solution for the subject. A lens barrel for a soft focus lens, characterized in that the distance between the position of the soft focus lens and the position where the image is obtained is set to be substantially equal.