JPH08179207A - Image pickup optical system - Google Patents

Abstract

PURPOSE: To improve the color reproducibility and to easily obtain an image of high resolution by making the front focal position of a rear lens group almost immobile at the time of varying a power and focusing. CONSTITUTION: A lens group 1 on more object side than a diaphragm 2 is provided with a lens group having variable power function, and the compensation of the movement of an image point at the time of varying the power and focusing are simultaneously performed by means of lens groups 4-6 on more image side than the diaphragm 2. The front focal position 11 of a rear lens group LR is made to be immobile at the time of varying the power and focusing. When the lens group 6 on more image side than the diaphragm 2 is moved e.g. as shown by an arrow 10 at the time of varying the power, at least another lens group e.g. the lens group 4 is moved as shown by an arrow 9 in order to make the front focal position 11 of the rear lens group LR spacially immobile. Namely, by moving at least two lens groups, the front focal position of the system including all moving lens groups on more image side than the aperture diaphragm 2 is made to be nearly fixed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image pickup optical system, and in particular, when the image pickup optical system is composed of a variable power optical system, the exit pupil of the variable power optical system is set at a position far from the image plane. An image side telecentric system, a separation optical system such as a color separation prism, a light beam splitting prism, and a beam splitter is provided on the image surface side, and a good image can be easily obtained when a CCD or the like is used as an image pickup means. The present invention relates to an image pickup optical system suitable for a camera or the like.

[0002]

2. Description of the Related Art Conventionally, various optical systems (zoom lenses) have been proposed which perform zooming or focusing by moving a lens group on the image plane side of a diaphragm. These zoom lenses have a feature that the entire lens system is relatively small and lightweight, and are often used as a photographing system for recent downsized video cameras.

Particularly, in a rear focus type zoom lens which performs zooming and focusing with a lens unit other than the first lens unit on the object side, a small and lightweight lens unit is moved during focusing, so that the driving force of the lens unit is small. It has features such as TESMI and quick focusing.

On the other hand, the light beam from the photographing system is divided into a plurality of light beams by the light splitting means, and an image based on each light beam is formed on a plurality of image pickup devices (CCD) to obtain high-definition image information and high resolution. Various image pickup devices such as a TV camera and a high-definition camera for color reproduction have been proposed. In order to obtain good color reproduction and high-resolution images in such an image pickup system, a so-called image in which a chief ray is made incident on a color separation system such as a color separation prism or a color filter or a CCD in a substantially vertical direction. A face-side telecentric system is used.

[0005]

In a TV camera, a video camera or the like, a color separation optical system such as a 3P prism provided on the image side has a structure in which a multilayer film is vapor-deposited on one surface of the prism for color separation. Generally, the color separation characteristic of the multilayer film has a dependency on the incident angle of the light ray, and therefore it is desirable that the incident angle of the light ray incident on the color separation optical system is substantially constant at each part of the image plane. Further, even in an image pickup system using an image pickup device such as a CCD that does not use a color separation optical system, since there is a gap between the color filter and the light receiving surface, the color separation performance also changes depending on the incident angle with respect to the image pickup device.

Therefore, the image pickup optical system is usually an image-side telecentric system so that both on-axis and off-axis rays are substantially parallel to the optical axis, and the incident angle to the multilayer film or the CCD is substantially constant. In the image side telecentric system, it is necessary that the exit pupil is located at a distance to the image plane.

However, in the case of an optical system in which the lens unit on the image side of the diaphragm moves during zooming or focusing, the exit pupil position may move as the lens unit moves. For this reason, it becomes difficult to keep the exit pupil position constant to some extent irrespective of the position of the lens group. For this reason, there is a problem that color shading or the like occurs due to a change in color separation characteristics depending on the lens group position.

On the other hand, various variable power optical systems have been proposed in which the exit pupil position is kept constant irrespective of variable power and focus. For example, in Japanese Unexamined Patent Publication No. Sho 49-112163, a focusing lens group that is fixed during zooming (magnification), a moving lens group for zooming, an aperture stop, a fixed lens group during zooming, and It is configured by arranging a lens group that moves during zooming,
The exit pupil position is kept constant by moving the diaphragm along with zooming. In this case, the aperture stop SP is used for the purpose of making the lens group closest to the object side, that is, the so-called front lens small.
Is arranged on the object side of the moving lens group in order to bring the lens closer to the object side as much as possible, and the movement of the exit pupil at that time is suppressed by moving the diaphragm itself.

However, this method has a problem that the front lens diameter increases because the lens unit L1 closest to the object side is used for focusing.

On the other hand, in JP-A-59-147313 and JP-A-59-222808, a first lens group that is fixed during zooming, a second lens group for zooming, an aperture stop, and a fixed third lens group. It is composed of a lens group and a fourth lens group that corrects an image plane variation due to zooming, and the diaphragm and the fourth lens group are moved according to zooming to reduce the movement of the exit pupil. This method describes that a focusing lens group may be provided on the image plane side of the diaphragm, but does not disclose a specific configuration.

According to the present invention, when zooming and focusing are performed with a part of the rear lens group on the image plane side of the aperture stop, by appropriately setting each lens group, the zoom lens can be zoomed and focused on the front side. When the color separation optical system, color filter, and image sensor are provided on the image side so that the focal position is kept constant, the color reproduction of the image capturing optical system is good and the image of high resolution can be easily obtained. For the purpose of provision.

[0012]

The image pickup optical system according to the present invention comprises: (1-1) a plurality of lens groups including a lens group that moves on the optical axis during zooming and focusing on the image plane side of the aperture stop. Is provided so that the front-side focal position of the rear lens group is substantially stationary during zooming and focusing.

(1-2) A rear lens group having a plurality of lens groups including a lens group that moves on the optical axis at the time of zooming and focusing is provided on the image plane side of the aperture stop, and the front side of the rear lens group is provided. It is characterized in that the focal position is substantially immovable with respect to the aperture stop when the magnification is changed or the focus is adjusted.

(1-3) From the object side, in order from the object side, the first group having a positive refractive power, the second group having a negative refractive power, the aperture stop, the third group having a positive refractive power, and the fourth group having a positive refractive power. The lens unit has four lens groups, and the second lens unit is moved to the image plane side to perform zooming from the wide-angle end to the telephoto end, and the image plane fluctuation due to zooming is moved to the fourth lens unit. At the same time as the correction, the fourth group is moved to perform focusing, and the aperture stop is moved on the optical axis during zooming and focusing, with respect to the front focus position of the rear lens group on the image plane side of the aperture stop. It is characterized in that the position of the aperture stop is substantially fixed.

(1-4) First group having positive refracting power, second group having negative refracting power, aperture stop, third group having positive refracting power, and fourth group having negative refracting power in order from the object side. , And a fifth lens unit having a positive refracting power, that is, the fifth lens unit, and the second lens unit is moved to the image plane side to perform zooming from the wide-angle end to the telephoto end, and the image plane fluctuation due to zooming. Is corrected by moving the fourth group and the fifth group, and the fourth group and the fifth group are moved to perform focusing, and the front focus position of the rear lens group on the image surface side of the aperture stop is substantially It is characterized by being immobile.

(1-5) First group having positive refracting power, second group having negative refracting power, aperture stop, third group having positive refracting power, and fourth group having positive refracting power in order from the object side. , And a fifth lens unit having a negative refracting power, the second lens unit is moved to the image plane side to change the magnification from the wide-angle end to the telephoto end, and the image plane fluctuation due to the magnification change Is corrected by moving the fourth group and the fifth group, and the fourth group and the fifth group are moved to perform focusing, and the front focus position of the rear lens group on the image surface side of the aperture stop is substantially It is characterized by being immobile.

(1-6) First group having positive refracting power, second group having negative refracting power, aperture stop, third group having fourth refracting power, fourth group, and fifth group, in order from the object side. Has five lens groups,
When the combined refractive power of the fourth group and the fifth group is positive, the second group is moved to the image plane side to perform zooming from the wide-angle end to the telephoto end, and It is characterized in that the group is moved to correct the image plane variation due to zooming and to focus so that the front focal position of the rear lens group on the image plane side of the aperture stop is substantially stationary.

[0018]

Embodiment 1 FIG. 1 is a schematic diagram of an image pickup optical system (variable magnification optical system) according to Embodiment 1 of the present invention. In the figure, 2 is an aperture stop.
Reference numeral 1 (LF) is a front lens group on the object side of the aperture stop 2 and has, for example, a lens group for zooming. Reference numeral LR denotes a rear lens group on the image plane side of the aperture stop 2. 3, 5,
Reference numeral 7 denotes a lens group that is fixed during zooming and focusing, 4 is a lens group that moves during zooming and / or focusing, and 6 is a lens group that corrects image plane variation due to zooming and performs focusing. Is the image plane (Gauss image plane).

Reference numeral 11 denotes a front focal position of the rear lens group LR (composite system of lens groups 3 to 7) closer to the image plane than the aperture stop 2. In this embodiment, the respective elements are appropriately set so that the front principal point position 11 is located in the vicinity of the aperture stop 2 so that the optical system as a whole becomes an image side telecentric system.

Then, a lens group having a zooming function is provided in the lens group 1 on the object side of the diaphragm 2, and the lens groups 4 to 6 on the image side of the diaphragm 2 simultaneously correct the image point movement due to zooming and focus. ing. The front focus position 11 of the rear lens group LR is configured to be stationary during zooming and focusing.

In this embodiment, when the lens group 6 on the image side of the aperture stop 2 is moved as shown by an arrow 10 during zooming, as shown in the figure, the front focus position 11 of the rear lens group LR is spatially divided. At least one more to immobilize
One lens group, for example, the lens group 4 is moved as shown by an arrow 9. That is, by moving at least two lens groups, the front focal position of the system including all the moving lens groups on the image side of the aperture stop 2 is made substantially constant.

In the present embodiment, in order to keep the front focal position constant, at least two lens groups of the rear lens group LR may be moved during zooming or focusing. As a result, the entire optical system becomes an image side telecentric system.

FIG. 2 is a schematic view of the essential parts of an image pickup optical system according to the second embodiment of the present invention. In this embodiment, 3P is provided on the image plane side of the image pickup optical system.
The case where the color separation optical system 22 including a prism is provided is shown. In the figure, reference numeral 21 denotes a rear lens group on the image plane side of the aperture stop 2, which has the same lens configuration as in FIG. The color separation prism 22 is a blue prism PB provided with a dichroic film (multilayer film) 28 for reflecting blue light.
It comprises a red prism PR provided with a red reflecting dichroic film (multilayer film) 29 and a green prism PG. Reference numerals 23, 24 and 25 denote image pickup surfaces, for example, provided with image pickup elements such as CCDs.

In the present embodiment, the light flux emitted from the lens group 1 on the object side of the diaphragm 2 is the lens group 21 on the image side of the diaphragm 2.
The light is collected by and enters the color separation optical system 22. At this time, the front focus position 11 of the lens group 21 is immovable with respect to the movement of each lens group in the lens group 21, and is in the vicinity of the stop 2 position. The entire optical system is an image-side telecentric system.

As a result, the angles at which the respective light beams are incident on the multilayer films 28 and 29 of the color separation optical system are substantially the same for the on-axis light beam 26 and the off-axis light beam 27, and the color shading is performed. Deterioration due to the incident angle dependency such as is reduced.

FIG. 3 is a schematic view of the essential portions of the paraxial refractive power arrangement of Numerical Example 1 of the variable power optical system as the image pickup optical system of the present invention. In the figure, L1 is a first group having a positive refractive power, L2 is a second group having a negative refractive power, SP is an aperture stop, and L3 is a third group having a positive refractive power.
L4 is a fourth lens unit having a negative refractive power, L5 is a fifth lens unit having a positive refractive power, and IP is an image plane.

In the present embodiment, the second lens unit is moved to the image plane side as indicated by the arrow when the magnification is changed from the wide-angle end to the telephoto end, and the image plane variation caused by the magnification change is caused by the fourth lens unit and the fifth lens unit. It is corrected by moving it while having a convex locus on the side.

Further, a focus type is adopted in which the fourth group and the fifth group have a predetermined relationship and are moved on the optical axis for focusing. Solid curves 3 of the fourth and fifth groups shown in FIG.
The curves 0 and 31 and the dotted curves 32 and 33 indicate the movement loci for correcting the image plane variation due to the zooming from the wide-angle end to the telephoto end when focusing on an infinite object and a short-distance object, respectively. Shows.

Next, a paraxial numerical example of the numerical value example 1 will be shown. In the numerical examples, fi: focal length of i-th group f: focal length of entire system ei: distance between i-th lens group and (i + 1) th lens group e2-s: distance between second lens group and aperture es-3 : Distance between diaphragm and second lens group fb: Back focus f45: Position of front focus of fourth / fifth lens group composition system measured from first lens group.

(Numerical Example 1) f1 = 27.581 f2 = -5.800 f3 = 17.066 f4 = -8.970 f5
= 10.000

[0031]

[Table 1] In the present embodiment, the amounts of movement of the fourth group and the fifth group when focusing on an object at infinity to a near object are m4 and m, respectively.
5, P4 and P5 are the refracting powers of the fourth and fifth groups, respectively, and P45 is the combined refracting power of the fourth and fifth groups when focusing on an object at infinity.

[0032]

[Equation 1] The fourth group and the fifth group are moved to the object side as indicated by arrow 34 so as to satisfy the above condition.

As a result, the front focal point of the rear lens group (L3, L4, L5) on the image side of the diaphragm SP is made to substantially coincide with the diaphragm SP position, and the exit pupil position is infinity in the entire zoom range and the entire object distance. I am trying to become. In this embodiment, the first and third groups are fixed during zooming and focusing.

FIG. 4 is a schematic view of a principal part of a paraxial refractive power arrangement of Numerical Example 2 of a variable power optical system as an image pickup optical system of the present invention. In the numerical example 2, the optical system on the object side of the aperture stop SP has the same configuration as the numerical example 1. Aperture stop SP
On the image side, the third lens unit L3 has a fixed positive refractive power, the fourth lens unit L4 has a positive refractive power, and the fifth lens unit L5 has a negative refractive power. The fourth and fifth groups move while maintaining the relationship represented by the equation (1) for focusing.

The solid curves 40 and 41 and the dotted curves 42 and 43 of the fourth and fifth groups are used for zooming from the wide-angle end to the telephoto end when focusing on an object at infinity and a near object, respectively. It is a movement locus when correcting the accompanying image plane variation. In this embodiment, with such a configuration, the front focal point of the rear lens group (L3, L4, L5) on the image side of the aperture stop SP is substantially aligned with the aperture SP position, and the exit pupil is in the front zoom range and the front object distance. The position is set to infinity.

Next, the numerical values of Numerical Example 2 are converted into Numerical Example 1
Similar to

Numerical Embodiment 2 f1 = 27.581 f2 = -5.740 f3 = 17.066 f4 = 15.000 f5
= -20.000

[0038]

[Table 2] FIG. 5 is a schematic view of a main part of a paraxial refractive power arrangement of Numerical Example 3 of a variable power optical system as an imaging optical system of the present invention. L in the figure
1 is the first group of positive refractive power, L2 is the second group of negative refractive power,
L3 is a third group having a positive refractive power, and L4 is a fourth group having a positive refractive power. SP is an aperture stop, which is arranged in front of the third lens unit L3. IP is the image plane.

In this embodiment, the second lens unit is moved to the image plane side as indicated by the arrow when the magnification is changed from the wide-angle end to the telephoto end, and the fourth lens unit is convex toward the object side due to the image plane variation due to the magnification change. It is corrected by moving while having the locus of. Further, the fourth group is moved to focus. The aperture stop SP is moved as shown by a curve 50 (52) during zooming from the wide-angle end to the telephoto end.

The aperture stop SP, the solid curves 50 and 51, and the dotted curves 52 and 53 of the fourth group shown in the figure are from the wide-angle end to the telephoto end when focusing on an infinite object and a short-distance object, respectively. The moving locus at the time of zooming is shown. still,
The first and third groups are fixed during zooming and focusing.

In the present embodiment, for example, when focusing on an object at infinity from a near object at the telephoto end,
As shown by the straight line 54 in the figure, this is done by moving the aperture stop SP and the fourth lens unit forward.

In this embodiment, the aperture stop SP is moved on the optical axis as described above at the time of zooming and focusing.
The front focal point of the rear lens group LR on the image side of the aperture stop SP is substantially aligned with the stop position so that the exit pupil position is substantially infinity over the entire zoom range and the entire object distance.

Next, the numerical values of Numerical Example 3 are set to Numerical Example 1
Similar to

Numerical Example 3 f1 = 28.0 f2 = -5.8 f3 = 21.0 f4 = 20.0

[0045]

[Table 3]

[0046]

As described above, according to the present invention, when performing zooming and focusing with a part of the rear lens group on the image plane side of the diaphragm, each lens group is appropriately set. When the magnification is changed and the focus is adjusted so that the front focal position is constant and a color separation optical system, color filter, and image sensor are provided on the image side, images with good color reproducibility and high resolution can be obtained. It is possible to achieve an imaging optical system that can easily obtain

[Brief description of drawings]

FIG. 1 is a schematic diagram of an optical system according to a first embodiment of the present invention.

FIG. 2 is a schematic diagram of an optical system according to a second embodiment of the present invention.

FIG. 3 is an explanatory diagram of a paraxial refractive power arrangement of an optical system according to Numerical Example 1 of the present invention.

FIG. 4 is an explanatory diagram of a paraxial refractive power arrangement of an optical system according to Numerical Example 2 of the present invention.

FIG. 5 is an explanatory diagram of a paraxial refractive power arrangement of an optical system according to Numerical Example 3 of the present invention.

[Explanation of symbols]

 L1 1st group L2 2nd group L3 3rd group L4 4th group L5 5th group SP Aperture stop IP image plane LF Front lens group LR Rear lens group

Claims (6)

[Claims] 1. A rear lens group having a plurality of lens groups including a lens group that moves on the optical axis at the time of zooming and focusing is provided closer to the image surface side than the aperture stop, and the front focus position of the rear lens group is An image pickup optical system characterized by being substantially fixed during zooming and focusing. 2. A rear lens group having a plurality of lens groups including a lens group that moves on the optical axis at the time of zooming and focusing is provided closer to the image surface side than the aperture stop, and the front focus position of the rear lens group is An imaging optical system characterized in that it is substantially immovable with respect to the aperture stop during zooming or focusing. 3. A first group having a positive refractive power, a second group having a negative refractive power, an aperture stop, a third group having a positive refractive power, and a fourth group having a positive refractive power in order from the object side. The second lens unit has two lens units, and the second lens unit is moved to the image plane side to change the magnification from the wide-angle end to the telephoto end, and the image plane variation due to the magnification change is corrected by moving the fourth lens unit. The fourth lens group is moved to perform focusing, and the aperture diaphragm is moved on the optical axis during zooming and focusing to adjust the aperture diaphragm to the front focus position of the rear lens group on the image plane side of the aperture diaphragm. The imaging optical system is characterized in that the position of is substantially fixed. 4. A first group having a positive refractive power, a second group having a negative refractive power, an aperture stop, a third group having a positive refractive power, a fourth group having a negative refractive power, and a positive group in order from the object side. Of the fifth lens group having a refracting power of 5, the second lens group is moved to the image plane side to change the magnification from the wide-angle end to the telephoto end, The fourth lens unit and the fifth lens unit are moved for correction, and the fourth lens unit and the fifth lens unit are moved for focusing, so that the front focus position of the rear lens unit on the image plane side of the aperture stop becomes substantially stationary. An imaging optical system characterized by the above. 5. A first group having a positive refractive power, a second group having a negative refractive power, an aperture stop, a third group having a positive refractive power, a fourth group having a positive refractive power, and a negative group in order from the object side. Of the fifth lens group having a refracting power of 5, the second lens group is moved to the image plane side to change the magnification from the wide-angle end to the telephoto end, The fourth lens unit and the fifth lens unit are moved for correction, and the fourth lens unit and the fifth lens unit are moved for focusing, so that the front focus position of the rear lens unit on the image plane side of the aperture stop becomes substantially stationary. An imaging optical system characterized by the above. 6. A first group having a positive refractive power, a second group having a negative refractive power, an aperture stop, a third group having a positive refractive power, a fourth group, and a fifth group in order from the object side. In a lens having a lens group and having a positive combined refractive power of the fourth group and the fifth group, the second group is moved to the image plane side to perform zooming from the wide-angle end to the telephoto end, The fourth lens group and the fifth lens group are moved to perform image plane variation correction and focusing due to zooming so that the front focus position of the rear lens group on the image plane side of the aperture stop is substantially immovable. Characteristic imaging optical system.