JP2981897B2 - camera - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a low-cost camera having a small number of components, and more particularly to an optical system mounted on such a camera.

(Prior Art) Conventionally, many low-cost cameras, particularly a lens mounted on a film with a lens as a prominent example, generally lack correction of spherical aberration. By increasing the number, a practically sufficient resolving power is obtained, and the depth of field is increased so that it can be used over a wide range of shooting distances. When trying to use such a camera in a state where the brightness is insufficient such as indoor photographing, a strobe having a large guide number must be combined in order to compensate for the insufficient brightness. However, it is difficult to give a large guide number to a strobe combined with a low-cost camera in terms of cost. Therefore, when the image is taken in a state where the brightness is insufficient, the image taken on the film is limited to only a small area at a very short distance due to the insufficient light amount of the strobe, and the area close to the imaging distance range of the fixed focus lens is close. I had to shoot only in the vicinity, which resulted in a so-called out-of-focus shot.

On the other hand, various cameras having a fixed focus lens provided with a strobe and a variable aperture mechanism are commercially available, and among these cameras, the lens mounted on an intermediate or higher class camera has a relatively high F-number. In many cases, the number is bright and the spherical aberration is corrected relatively well. In addition, since a strobe with a relatively large guide number is mounted on the strobe and the aperture is also a variable aperture mechanism, there is no problem seen in the low-cost camera as described above.

However, of course, the mechanism becomes more complicated and the cost cannot be avoided.

(Problems to be Solved by the Invention) The present invention overcomes such disadvantages of the prior art, is low-cost, and is suitable for short-distance shooting in a low-illuminance environment where the brightness is insufficient such as in a room. It is an object of the present invention to obtain a camera having good performance in a close range direction over a wide range of shooting distance. More specifically, an attempt is made to obtain a low-cost camera having a lens having an F number of about 5.6 to 8.0.

(Means for Solving the Problem) The features of the camera of the present invention are as follows. (1) First, in a camera having a fixed focus lens provided with a variable aperture mechanism, the fixed focus lens is provided with a spherical aberration caused by the lens. Utilizing the movement of the best image point position of the lens along with the aperture, the aperture is narrowed down at the time of long-distance shooting, the aperture is opened at the time of short-distance shooting, and a lens having spherical aberration that can change the focused object distance. In addition to the above, the variable aperture mechanism is characterized in that the aperture is stopped down at the time of long-distance shooting, and is opened at the time of short-distance shooting.

(2) Secondly, a stroboscope is made to emit light at the time of close-up shooting.

(3) It is desirable that the number of the lenses is two or less.

(4) Further, the amount of movement of the focused object position △ X due to the movement of the MTF best focus position of the lens due to the narrowing down due to the spherical aberration of the lens, the hyperfocus position at the time of long-distance shooting, the maximum reach distance of the strobe light, It is desirable that the difference ΔY is approximately equal.

(Operation) The camera of the present invention has the fixed focus lens provided with the variable aperture mechanism as described above, and is provided with a strobe as necessary, and utilizes the movement of the MTF best focus position of the lens. In addition, a lens having a spherical aberration capable of changing the focused object distance by opening the aperture down for a long distance shooting and opening the aperture for a short distance shooting is mounted. This solves the problems described in the section of the prior art described above, and is low-cost, and when shooting at a close distance in a low-illumination environment where the brightness is insufficient such as in a room, a wider range is obtained in a closer distance direction. This makes it possible to obtain a good image over the shooting distance.

More specifically, as described in the section of the prior art, the lens mounted on a low-cost camera generally has insufficient correction of spherical aberration. It has a so-called undercorrection spherical aberration that focuses at a point closer to the lens.

When such a lens is incorporated into a camera as a fixed focus lens and the aperture is variable, if this aperture is changed according to the object distance, the movement of the MTF best focus position of the lens due to the aperture stop due to the spherical aberration of the lens In other words, when the aperture is set to a small aperture, the camera focuses on a distant object, and when the aperture is open, the camera focuses on a close object. The inventors have found and applied this to a low-priced camera with a fixed focus, so that a camera that can obtain a practically sufficient focus over a wide range of shooting distances by changing the aperture while having a fixed focus. Was obtained.

 Considering the present invention in terms of the depth of focus, the following is obtained.

In the fixed focus lens, the film plane is set to the best image point position with respect to the hyperfocal distance so that the infinity and the close distance are within the depth of focus with respect to a predetermined allowable circle of confusion. Here, assuming that the F number is F and the allowable confusion circle diameter is δ, the focal depth t on one side is approximated by t = F · δ.

The F number is represented by F = f (1+ | M |) / D, where f is the focal length, M is the photographing magnification, and D is the entrance pupil diameter. Since M | << 1, the change in the F-number due to the photographing magnification is not considered here.

Also, F-number F ₂ when if F number is ₁ aperture diameter phi when the F _1, the aperture diameter becomes phi ₂
Is F ₂ = F ₁ · φ ₁ / φ ₂

Next, a description will be given assuming that the open F number and the aperture diameter on the far side are F ₁ and φ ₁ , respectively, and the open F number and the aperture diameter on the short distance side are F ₂ and φ ₂ , respectively. That is, F ₁ > F ₂ ,
φ ₁ <φ ₂ .

FIG. 1 shows the depth of focus at the time of shooting on the far side. For the object distance from infinity to a finite distance U ₁ lies within the depth of focus, but if the short distance from U ₁ becomes unusable exceeds the permissible circle of confusion δ on the film surface. In conventional fixed-focus lens, the U ₁ has been a minimum shooting distance.

Here, assuming that the F number is F ₂ at the subject distance U ₁ , the depth of focus is halved as shown in FIG. 2, but the movement of the best image point position ΔB (the traveling direction of the light ray is positive) is , (F ₁ −F ₂ ) · δ <− △ B In other words, if (1−φ ₁ / φ ₂ ) F ₁ δ <− △ B, both the near side and the object can be within the depth of focus than U _1. it can, close distance is shortened up to U _2. However,-△
If B exceeds (F ₁ + F ₂ ) · δ = (1 + φ ₁ / φ ₂ ) F ₁ δ, B goes out of the depth of focus on the opposite side.
ΔB needs to satisfy the following conditions.

(1−φ ₁ / φ ₂ ) F ₁ δ <− △ B <(1 + φ ₁ / φ ₂ ) F ₁ δ Note that there is some discussion about the best image point. Gaussian method using distribution,
Although a method using a spot diagram (for example, “Optical Technology Research Association“ Lens Design Technique ”) is famous, in the embodiment of the present invention, the point at which the MTF for a spatial frequency of 30 lines / mm takes the maximum value is regarded as an improved image point. I have. The minimum diameter of the circle of confusion is considered to be 0.03 mm for a 35 mm film. (Photo camera publisher "Camera Technology Handbook") In the case of a low-priced camera according to the present invention, as described in the section of the prior art, the strobe combined with the camera has a very large guide number in terms of cost. It is difficult to provide a camera that can focus on a wide range of shooting distances in the closest distance direction when shooting at a short distance in a low-light environment where the brightness is insufficient such as in a room. However, the flash performance cannot keep up with the camera. In order to prevent this, it is desirable to emit a strobe light at the time of short-range shooting as shown in the condition (2). At the time of close-up shooting, the aperture is open, so that a sufficient amount of exposure can be obtained even with a low-emission flash, and in the case of a low-priced camera according to the present invention, when the aperture is opened, In addition, since an object at a short distance is brought into focus, particularly excellent performance can be exhibited in a low-illuminance and short-distance shooting environment.

Applying this to general shooting conditions, when the aperture is narrowed down, the aperture value is suitable for shooting in a bright environment, for example, outdoors in sunny weather. A focused photograph can be obtained from an object at a short distance to an object at a short distance. Conversely, when the aperture is wide open, the aperture value is suitable for shooting in a dark environment, for example, indoors. You can get a photo. In addition, the lack of light from the strobe is not a problem for objects at short distances, so a strobe with a small guide number may be used,
This makes it suitable for low-cost cameras.

In consideration of the cost of the low-priced camera, it is desirable that the number of lenses is two or less as shown in the condition (3). In the lens having such a simple structure, the spherical aberration tends to be undercorrected, and the condition (1)
The configuration as described in (2) can be utilized. If the number of lenses exceeds two, the cost increases, and the object of the present invention to obtain a camera having good performance at low cost cannot be achieved.

It is of course possible to implement a low-priced camera according to the present invention as a film with a lens, and in this case, a film with a lens having a wider range of use can be provided.

(Example) Hereinafter, an example of the camera of the present invention will be described. Table 1 shows lens data of the first embodiment of the lens system mounted on the camera of the present invention. Table 2 shows lens data of a second embodiment of the lens system mounted on the camera of the present invention. FIG. 3 is a sectional view of a first embodiment of a lens system mounted on the camera of the present invention. FIG. 4 is a cross-sectional view of a second embodiment of the lens system mounted on the camera of the present invention. The figure is a spherical aberration diagram of a first embodiment of a lens system mounted on a camera of the present invention,
FIG. 6 shows a second example of the lens system mounted on the camera of the present invention.
FIG. 7 shows a spherical aberration diagram of the embodiment, and FIG. 7 shows a spatial frequency of 30 lines / mm of the first embodiment of the lens system mounted on the camera of the present invention.
8 shows the MTF versus defocus characteristic curve at the spatial frequency of 30 lines / mm in the second embodiment.

Looking at the first embodiment, as can be seen from the characteristic curve in FIG. 7, when the lens is used as F13.0,
The image point position where the MTF value of the spatial frequency 30 lines / mm is the maximum is at a position of -0.4 mm with respect to the Gaussian surface of the lens as a zero reference, and when used as F8.5, the spatial frequency 30 lines / mm M
It can be seen that the image point position where the TF value is maximum is at the position of -0.6 mm. The difference between the image point positions at F13.0 and F8.0
The fact that there is 0.2 mm means that when the hyperfocal position of the lens at F8.0 is set to 3.0 m and the lens is fixed, when the aperture is stopped down to F13.0, an object near 6.0 m is in focus.

Similarly, in the second embodiment, as can be seen from FIG. 8, when the lens is used at F11.6, the MT of the spatial frequency is 30 / mm.
The image point position at which F is the maximum is at a position of -0.2 mm with the Gaussian surface of the lens being zero, and when used as F5.8,
The image point position at which the MTF value at a spatial frequency of 30 lines / mm is the maximum is-
It can be seen that it is located at 0.4 mm. The difference of 0.2 mm between the image point positions at F11.6 and F5.8 is that when the hyperfocal position of the lens at F5.8 is set to 1.7 m and the lens is fixed, at F11.6 the object near 3.6 m You will be in focus.

The aspherical shape in the lens data in the table is represented by a rectangular coordinate system with the vertex of the surface as the origin and the optical axis direction as the X axis.
When the vertex curvature is C, the conic coefficient is K, the aspheric coefficient is A _i , and the width of the aspheric surface is P _i , It is represented by

 Each symbol in the table indicates the following.

r _i : paraxial radius of curvature d _i : interplanar spacing n _d : refractive index at d-line of lens material ν _d : Atsube number Open stop diameter for long distance φ ₁ = 2.26 mm (F13.0) Open stop diameter for short distance φ ₂ = 3.45 mm (F8.50) B = -0.20 (U = 3.0 m) When δ = 0.03 ( _{1-φ 1 / φ 2)} F 1 δ = 0.13 (1 + φ 1 / φ 2) F 1 δ = 0.65 Long range open aperture diameter φ ₁ = 2.70mm (F11.6) short-distance open aperture diameter _{φ 2 = 5.40mm (F5.80) △} B = 0.23 (U = 1.8m) when the [delta] = 0.03 (1 -Φ ₁ / φ ₂ ) F ₁ δ = 0.17 (1 + φ ₁ / φ ₂ ) F ₁ δ = 0.52 In addition, the flash emission control works in conjunction with changing the distance between the apertures and only when the aperture is changed to the short distance aperture. What is necessary is just to emit light.

(Effects of the Invention) As can be seen from the above embodiment and the drawings, the camera of the present invention has a very simple structure with a fixed-focus type lens mount, but the brightness of the room or the like can be adjusted by adjusting the aperture. In short-distance photography in a low-illuminance environment where the brightness is insufficient, a camera having excellent performance over a wide range of photographing distances by a closer distance method can be obtained at low cost and with excellent performance.

[Brief description of the drawings]

FIG. 1 is a conceptual diagram of the depth of focus for a long distance for explaining the operation of the present invention, FIG. 2 is a conceptual diagram of the depth of focus for the short distance, and FIG. 3 is a conceptual diagram of a lens system mounted on the camera of the present invention. FIG. 4 is a sectional view of the second embodiment, FIG. 5 is a spherical aberration chart of the first embodiment, FIG. 6 is a spherical aberration chart of the second embodiment, FIG. The figure shows the MTF versus defocus characteristic curve at a spatial frequency of 30 lines / mm of the first embodiment, and FIG. 8 shows the MTF versus defocus characteristic curve at a spatial frequency of 30 lines / mm of the second embodiment.

Claims (3)

(57) [Claims] 1. A camera having a fixed focal length lens provided with a variable aperture mechanism, wherein the fixed focal length lens is photographed at a long distance by utilizing the movement of the best image point position of the lens as the lens is narrowed down by spherical aberration. Sometimes narrow the aperture,
At the time of close-up shooting, the aperture is opened, and a lens having a spherical aberration that can change the focused object distance is used, and the variable aperture mechanism closes down the aperture at the time of long-range shooting, and opens the aperture at the time of short-range shooting. Camera characterized by the following 2. A camera according to claim 1, wherein a strobe light is emitted at the time of a short-distance photographing. 3. The camera according to claim 1, wherein the number of said lenses is two or less.