JPH10123416A - Image pickup size conversion optical system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image pickup size conversion optical system which is constituted so that the angle of view may not be changed even when a photographing lens is attached to a camera whose image pickup element size is different and it can cope with many kinds of cameras, and which is made small in size and light in weight and bright. SOLUTION: This optical system is provided with a photographing lens having a focusing part G1 , variable power parts G2 and G3 and an image-formation part G4 , and a conversion lens group GC in order from an object side, and formed so that it can be converted to be the different kind of image pickup size by attaching/detaching the conversion lens group GC in the optical path of the photographing lens. In such a case, the image-formation part G4 of the photographing lens has a front group G4 F and a rear group G4 B. In the case of attaching the conversion lens group GC in the optical path of the photographing lens, all of or a part of the front group G4 F of the image- formation part is moved to an image surface side and the conversion lens group GC is attached to the object side of the moved lens group.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an imaging optical system such as a video camera and a silver halide film camera, and more particularly to an imaging size conversion optical system formed so as to be convertible into different types of imaging sizes.

[0002]

In recent years, the size of solid-state imaging devices used in video cameras and the like has been reduced year by year in order to reduce the size of the entire camera and improve the yield (throughput) of the solid-state imaging devices. Tend to go.
For example, in a consumer video camera that does not care much about image quality, a 1/3 inch size solid-state image sensor is mainstream,
Recently, a 1/4 inch, and even 1/5 inch size solid-state imaging device has been developed. In broadcast and professional video cameras that require high image quality, solid-state image pickup devices of 2/3 inch size and 1/2 inch size are still mainstream, and high-definition video cameras that require the highest image quality. , Solid-state imaging devices having a size of 1 inch are still mainstream. That is, as described above, at present, there are cameras equipped with various image pickup devices for various applications, and corresponding photographic lenses corresponding to the respective sizes exist.

Therefore, for example, when a photographing lens for a 2/3 inch image pickup device is mounted on a video camera equipped with a 1/2 inch image pickup device, the image forming area of the 2/3 inch photographing lens becomes 1
Since the photographing area of the / 2 inch image sensor is completely covered, there is no vignetting of light rays. However, since the imaging area of the 1/2 inch image sensor does not cover the imaging area of the 2/3 inch imaging lens, a phenomenon occurs in which the imaging area shifts to the telephoto side. In other words, if the photographing lens for a large image sensor is used for a camera equipped with a small image sensor to share the lens in order to increase the operation efficiency of the camera lens, the wide-angle side becomes insufficient.

In order to solve this problem, Japanese Patent Application Laid-Open No.
As in 6012, there is a method of inserting a re-imaging optical system between the taking lens and the camera. However, in this method, an image forming lens that makes the image forming surface of the photographing lens and the image pickup device surface have a conjugate relationship and a prism system that prevents image inversion are required, so that the optical system becomes very large and heavy. . In addition, since the size of the prism for preventing image inversion is restricted, the optical system cannot be made bright. In an imaging size conversion optical system as disclosed in Japanese Patent Application Laid-Open No. 2-262113, a conversion lens system for performing conversion must have at least a configuration of a negative lens group and a positive lens group, that is, a so-called inverted Galilean type. Accordingly, a wide space for inserting the conversion lens group must be secured, and the entire lens system becomes large.

Further, in the optical systems disclosed in JP-A-6-303469 and JP-A-6-230279, the entire image forming portion (relay lens system) of the photographing lens body or the front group is exchanged together to convert the magnification. This system is not preferable because not only the number of lenses constituting the conversion lens group must be increased but also a space for replacement must be provided. In view of the above, the present invention solves the above-mentioned drawbacks, so that the angle of view does not change even when a photographing lens is attached to cameras having different image sensor sizes, and the camera is compatible with more cameras, and is small, light and bright. It is an object to provide a size conversion optical system.

[0006]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention comprises a photographing lens having a focusing section, a variable magnification section, and an image forming section in order from the object side, and a conversion lens group. In an imaging size conversion optical system formed so as to be convertible to different types of imaging sizes by attaching / detaching a conversion lens group in the optical path of the lens, the imaging unit of the imaging lens has a front group and a rear group, When mounting the lens group in the optical path of the taking lens, all or a part of the front group of the imaging unit is moved to the image plane side, and the conversion lens group is mounted on the object side of the moved lens group. To provide an imaging size conversion optical system.

When the conversion lens group is formed to have a negative refractive power, the conversion lens group is placed in the optical path of the photographing lens, thereby reducing the image circle originally supposed to be formed by the photographing lens. Therefore, when a photographing lens for a large image pickup device is attached to a camera having a small image pickup device, an image that goes out of the image pickup region of the image pickup device is reduced, so that the image enters the image pickup region of the image pickup device.

At this time, the conversion lens group of the conventional image pickup size conversion optical system requires a lens group having a negative refractive power and a lens group having a positive refractive power. All or part of the front group of the unit is moved to the image plane side, and the conversion lens group is mounted on the object side of the moved lens group, so the conversion lens group is only one of the positive or negative lens group Can be configured. As a result, the lens configuration of the conversion lens group can be simplified. Also, for the taking lens, it is not always necessary to secure a space for mounting the conversion lens group, and it is sufficient that the conversion lens group can be mounted after moving all or a part of the front group of the imaging unit in the optical axis direction. Therefore, the size of the photographing lens is not increased. Thus, by employing the arrangement of the present invention, a good and lean lens system can be achieved.

In the present invention, Y ₁ : the maximum image height of the taking lens when the conversion lens group is not attached Y ₂ : the maximum image height of the taking lens when the conversion lens group is attached f _M : image formation of the taking lens the focal length f _R sector: when a focal length of the conversion lens _{group, 0.4 <Y 2 / Y 1} <0.95 (1) | _{becomes> Y 2 / Y 1 (2} ) | f R / f M Preferably, the condition is satisfied.

Conditional expression (1) shows the zoom ratio when the conversion lens group is mounted. If the lower limit of conditional expression (1) is exceeded, the power of the conversion lens group must be increased, and as a result, it becomes difficult to correct aberrations, particularly to correct spherical aberration. Conversely, if the value exceeds the upper limit of the conditional expression (1), the power of the conversion lens unit is weakened, but the reduction magnification is too small, and the focal length of the entire system differs between when the conversion lens unit is attached and when it is removed. Not too much, and not a use with a beneficial effect. Conditional expression (2) shows the power distribution between the conversion lens group and the imaging unit. If the power distribution is out of the range of the conditional expression (2), the fluctuation amount between the exit pupil of the projection lens when the conversion lens group is removed and the exit pupil when the conversion lens group is mounted becomes too large. It also causes color shedding.

In the present invention, when _fMf is the focal length (unit: mm) of the lens group which moves to the image plane side when the conversion lens group is mounted, 10 < _fMf <300 (3) Preferably, the condition is satisfied. If the lower limit of conditional expression (3) is exceeded, not only is it difficult to correct aberrations or it is difficult to manufacture,
For an arbitrary conversion imaging size, the amount of movement of the lens group moving to the image plane side is extremely small, and a space for mounting the conversion lens group cannot be secured. Conversely, when the value exceeds the upper limit of conditional expression (3), the power of the lens unit that moves to the image plane side becomes weak, but the amount of movement becomes extremely large for an arbitrary converted imaging size, and the amount of movement becomes large. In this case, the entire length of the photographing lens of the main body becomes too long.

By attaching and detaching the conversion lens group in the optical path of the imaging lens, not only the focal length of the photographing lens can be changed, but also by moving the conversion lens group in the optical axis direction, the focus at the time of focusing can be obtained. It is also possible to correct the movement. Further, by moving the conversion lens group in the optical axis direction, it is possible to obtain a zooming effect. By moving the conversion lens group in a direction intersecting the optical axis, it is also possible to obtain a blur prevention function. is there.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of an imaging size conversion optical system according to the present invention will be described below. FIG. 1 is a lens configuration diagram of a photographic lens when no conversion lens group is mounted on the first embodiment and the second embodiment. FIGS. 2 and 3 show the main parts of the taking lens when the conversion lens groups of the first embodiment and the second embodiment are mounted, respectively. That is, the first embodiment and the second embodiment have the same configuration of the photographic lens body, although the conversion lens group is different.
The photographic lens of each of the embodiments includes, in order from the object side, a focusing unit, a variable power unit, and an imaging unit, and the focusing unit includes a first lens having a positive refractive power.
It is constituted by a lens group G _1. The zooming unit has a negative refractive power and moves from the object side to the image plane side along the optical axis when zooming from the wide-angle end to the telephoto end.
_2, is constituted by the third lens group G ₃ to move along the optical axis so as to correct image plane variation due to zooming. The imaging unit is a fourth lens group front group G _4F having a positive refractive power.
And a rear group G _{4B of} the fourth lens group having a positive refractive power. The imaging size of the photographic lens is converted as follows. That is, in the first embodiment, the fourth
All of front group G _4F moves toward the image plane side, on the object side of the fourth front group G _4F moved, mounting the conversion lens group G _C having a negative refractive power. In the second embodiment, the fourth
A part of the front lens group G _4F is moved to the image plane side, and the conversion lens group G having a negative refractive power is placed on the object side of the moved lens group.
_The image pickup size is converted by attaching _C.

Table 1 below shows the specifications of the photographic lenses of the first embodiment and the second embodiment. In Table 1, in [overall specifications], f represents the focal length of the entire system, and Y represents the image height. In [Lens Specifications], the first column No is the number of each lens surface from the object side, the second column r is the radius of curvature of each lens surface, the third column d is the distance between each lens surface, and the fourth column ν is D-line of each lens (λ = 58
7.6 nm) Abbe number based on the refractive index column 5 n _d for the d-line of each lens, at column 6 represents the lens number belongs each lens. The lens surface marked with * in the first column indicates an aspheric surface, and r of the aspheric lens surface indicates the radius of curvature of the vertex. The aspherical shape is a shape represented by the following equation. The conic constant κ and the aspheric coefficient C _n of the aspheric lens surface are shown in [Aspheric Data]. All aspheric coefficients C _n not shown in [Aspheric data] are zero. Here, y: height from the optical axis S (h): distance in the optical axis direction from the aspheric surface to the tangent plane at height y from the optical axis r: paraxial radius of curvature κ: conical constant C _n : n-th The following aspheric coefficient is In each of the embodiments, a parallel plane plate such as a color separation prism and various filters is disposed between the final surface of the lens and the image surface, and aberrations are corrected including these. The original is also shown.

The following Tables 2 and 3 respectively show the first
The specifications of the taking lens when the conversion lens group G _{C according} to the embodiment and the second embodiment are mounted will be described. However, the first embodiment shown in Table 2 is the same as Table 1 from the first surface to the twentieth surface and the twenty-eighth surface and thereafter, and therefore will not be described. Similarly, for the second embodiment shown in Table 3, the first to 21st surfaces and the second
Since the eight surfaces are the same as those in Table 1, the description is omitted. In Table 2, the lens surfaces a1 to a3 are the conversion lens groups G _C , and in Table 3, the lens surfaces b1 to b3 are the conversion lens groups G _C.

[0016]

[Table 1]

[0017]

[Table 2] [General _{Data] f = 6.77~124.3 Y 2 = 4.5mm} f R = -155.0 f M = 54.6 f Mf = 35.6 [ Lens _{Data] No r d ν n d 20} -138.389 (d 20) _{a1 -34.199 2.50 27.61 1.75520 G C a2} -32.073 1.50 82.52 1.49780 G C a3 -70.761 2.70 21 -105.322 4.70 64.10 1.51680 G 4F 22 -30.168 0.10 23 54.182 5.20 69.98 1.51860 G 4F 24 -115.102 0.10 25 50.239 6.70 65.77 1.46450 G 4F _{26 -54.000 2.00 39.82 1.86994 G 4F 27} 561.006 31.54 28 41.484 6.10 65.77 1.46450 G 4B [ condition correspondence _{value] Y 2 / Y 1 = 0.82} | f R / f M | = 2.84

[0018]

[Table 3] [General _{Data] f = 6.77~124.3 Y 2 = 4.5mm} f R = -440.7 f M = 35.6 f Mf = 66.3 [ Lens _{Data] No r d ν n d 21} -105.322 4.70 64.10 1.51680 G _{4F 22 -30.168 4.10 b1 -57.068 1.50 82.52} 1.49780 G C b2 -194.775 2.50 27.61 1.75520 G C b3 -99.216 4.70 23 54.182 5.20 69.98 1.51860 G 4F 24 -115.102 0.10 25 50.239 6.70 65.77 1.46450 G 4F 26 -54.000 2.00 39.82 1.86994 G _{4F 27 561.006 25.54 28 41.484 6.10 65.77} 1.46450 G 4B [ condition correspondence _{value] Y 2 / Y 1 = 0.82} | f R / f M | = 12.38

FIG. 4 shows the first embodiment and the second embodiment.
5 shows spherical aberration, astigmatism, and distortion at the wide-angle end and the telephoto end of the taking lens when no conversion lens group is attached. FIGS. 5 and 6 show various aberrations of the taking lens when the conversion lens units of the first and second embodiments are mounted, respectively. In the astigmatism diagram, a dotted line indicates a meridional image plane, and a solid line indicates a sagittal image plane. As is clear from the aberration diagrams, both examples have good imaging performance both when the conversion lens group is removed and when the conversion lens group is attached.

[0020]

As described above, according to the present invention, it is possible to obtain an imaging size conversion optical system in which the angle of view does not change even when the imaging lens is attached to cameras having different imaging element sizes, and the conversion lens group can be appropriately adjusted. Because of the arrangement, a compact, lightweight and high-performance imaging size conversion optical system is realized while simplifying the lens system.

[Brief description of the drawings]

FIG. 1 is a lens configuration diagram of a photographing lens when a conversion lens group according to a first embodiment and a second embodiment of the present invention is not mounted.

FIG. 2 is a diagram illustrating a main part of a taking lens when the conversion lens group according to the first embodiment is mounted.

FIG. 3 is a diagram illustrating a main part of a taking lens when a conversion lens group according to a second embodiment is mounted.

FIG. 4 is a diagram illustrating various aberrations of the photographing lens when the conversion lens unit according to the first embodiment and the second embodiment is not mounted.

FIG. 5 is a diagram illustrating various aberrations of the photographing lens when the conversion lens unit according to the first embodiment is mounted.

FIG. 6 is a diagram illustrating various aberrations of the photographing lens when the conversion lens unit according to the second embodiment is mounted.

[Explanation of symbols]

G ₁ … first lens group (focusing part) G ₂ … second
Lens group (magnification section) G ₃ ... third lens group (magnification section) G _4F ... fourth
Lens group front group (imaging unit) G _4B ... fourth lens group rear group (imaging unit) G _C ... conversion lens group

Claims (5)

[Claims] 1. A photographing lens having a focusing unit, a zooming unit, and an image forming unit in order from an object side, and a conversion lens group. By attaching and detaching the conversion lens group in the optical path of the photographing lens, In an imaging size conversion optical system formed so as to be convertible to different types of imaging sizes, the imaging unit of the imaging lens has a front group and a rear group, and when the conversion lens group is mounted on the optical path of the imaging lens. An imaging size conversion optical system, wherein the whole or a part of the front group of the imaging unit is moved to the image plane side, and the conversion lens group is mounted on the object side of the moved lens group. 2. The imaging size conversion optical system according to claim 1, wherein the lens group moving to the image plane side has a positive refractive power, and the conversion lens group has a negative refractive power. 3. The conversion lens group includes at least one negative lens, and at least one of the negative lenses has an object-side surface concave toward the object surface. 3. The imaging size conversion optical system according to 1 or 2. 4. The imaging size conversion optical system according to claim 1, wherein said conversion lens group has at least one cemented lens. 5. The imaging size conversion optical system according to claim 1, wherein the following condition is satisfied. _{0.4 <Y 2 / Y 1 <} 0.95 | f R / f M |> Y 2 / Y 1 where, Y _1: The conversion lens of the taking lens when not wearing the group maximum image height Y _2: the The maximum image height f _M of the photographing lens when the conversion lens group is attached: f _M : focal length of the imaging portion of the photographing lens f _R : focal length of the conversion lens group.