WO2016147501A1 - Image pickup optical system - Google Patents

Image pickup optical system Download PDF

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Publication number
WO2016147501A1
WO2016147501A1 PCT/JP2015/084350 JP2015084350W WO2016147501A1 WO 2016147501 A1 WO2016147501 A1 WO 2016147501A1 JP 2015084350 W JP2015084350 W JP 2015084350W WO 2016147501 A1 WO2016147501 A1 WO 2016147501A1
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Prior art keywords
optical system
lens group
imaging optical
imaging
wide
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PCT/JP2015/084350
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French (fr)
Japanese (ja)
Inventor
藤原　和人
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オリンパス株式会社
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Priority to JP2016557324A priority Critical patent/JPWO2016147501A1/en
Publication of WO2016147501A1 publication Critical patent/WO2016147501A1/en

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    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B15/00—Optical objectives with means for varying the magnification
    • G02B15/14—Optical objectives with means for varying the magnification by axial movement of one or more lenses or groups of lenses relative to the image plane for continuously varying the equivalent focal length of the objective
    • G02B15/144—Optical objectives with means for varying the magnification by axial movement of one or more lenses or groups of lenses relative to the image plane for continuously varying the equivalent focal length of the objective having four groups only
    • G02B15/1441—Optical objectives with means for varying the magnification by axial movement of one or more lenses or groups of lenses relative to the image plane for continuously varying the equivalent focal length of the objective having four groups only the first group being positive
    • G02B15/144113—Optical objectives with means for varying the magnification by axial movement of one or more lenses or groups of lenses relative to the image plane for continuously varying the equivalent focal length of the objective having four groups only the first group being positive arranged +-++
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B1/00—Instruments for performing medical examinations of the interior of cavities or tubes of the body by visual or photographical inspection, e.g. endoscopes; Illuminating arrangements therefor
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B23/00—Telescopes, e.g. binoculars; Periscopes; Instruments for viewing the inside of hollow bodies; Viewfinders; Optical aiming or sighting devices
    • G02B23/24—Instruments or systems for viewing the inside of hollow bodies, e.g. fibrescopes

Definitions

  • the present invention relates to an imaging optical system, and particularly to an imaging optical system mounted on a camera head for a rigid endoscope.
  • a camera head for a rigid endoscope has been used to shoot an observation image of a rigid endoscope and display it on a monitor.
  • the camera head includes an imaging element and an imaging optical system that forms an image on the imaging surface of the imaging element with light emitted from an eyepiece provided at the proximal end of the rigid endoscope, and the proximal end of the rigid endoscope Used in connection with.
  • an imaging optical system one having a zoom function is known (see, for example, Patent Documents 1 and 2).
  • the three-plate type imaging device includes a dichroic prism that divides incident light into light of three colors of R, G, and B, and three imaging elements that photograph three colors of light divided by the dichroic prism. Yes.
  • the imaging optical systems described in Patent Documents 1 and 2 have a problem that it is difficult to suppress color shading that occurs with zooming when applied to a three-plate imaging apparatus. That is, in the state where the endoscope camera head is connected to the rigid endoscope, the exit pupil position of the rigid endoscope becomes the entrance pupil position of the imaging optical system. Therefore, when zooming is performed by the imaging optical system, the entrance pupil position of the imaging optical system is constant, and the exit pupil position of the imaging optical system moves. As the exit pupil position of the imaging optical system moves, the incident angle of the light beam incident on the dichroic prism from the imaging optical system changes, and the light beam is incident on the dichroic prism with an inclination with respect to the optical axis.
  • the dichroic prism has a reflecting surface made of a multilayer interference film that selectively transmits light of a specific wavelength and reflects light of other wavelengths in order to decompose incident light into three colors of light.
  • the incident angle of the light beam on the reflecting surface changes, the optical path length of the light beam inside the multilayer interference film changes, so that the transmission wavelength of the reflecting surface changes. Therefore, when the incident angle of the light beam from the imaging optical system to the dichroic prism is tilted with magnification, the color of the light emitted from the dichroic prism also changes, and as a result, the endoscopic image displayed on the monitor Color shading with different colors at the top and bottom occurs in the vertical direction.
  • Patent Documents 1 and 2 disclose imaging optical systems having a large zoom ratio, but these imaging optical systems have a large amount of movement of the exit pupil position at the time of zooming, so they are combined with a three-plate imaging device.
  • the change in the incident angle of the light beam to the dichroic prism cannot be suppressed, and the color shading cannot be suppressed.
  • the present invention has been made in view of the above-described circumstances, and an object thereof is to provide an imaging optical system that can suppress color shading during zooming while having a large zoom ratio.
  • the present invention provides the following means.
  • the present invention is incorporated in the camera head connected to the proximal end of the rigid endoscope so that the body-mounted surface abuts the proximal end surface of the eyepiece part including the eyepiece of the rigid endoscope, and is incident from the eyepiece
  • An imaging optical system that forms an image of light, which can be zoomed between the wide-angle end and the telephoto end, has a zoom ratio of 1.5 times or more, and in order from the object side to the image side, A first lens group having a positive refractive power; a second lens group having a negative refractive power; a third lens group having a positive refractive power; and a fourth lens group having a positive refractive power;
  • An imaging optical system that satisfies the following conditional expressions (1) and (2) is provided.
  • ffw is the front focal position of the imaging optical system at the wide-angle end with the body-mounted surface as the origin
  • fw is the focal length of the entire system of the imaging optical system at the wide-angle end
  • fft is the body-mounted surface Is the front focal position of the imaging optical system at the telephoto end with the origin as the origin
  • ft is the focal length of the entire system of the imaging optical system at the telephoto end
  • h is the maximum image height on the imaging plane of the imaging optical system
  • D is the exit pupil position of the rigid endoscope with the torso surface as the origin
  • the optical axis direction from the object side to the image side is positive.
  • the imaging optical system of the present invention is used by being disposed between the rigid endoscope and the imaging element so that the rigid endoscope is positioned on the object side and the imaging surface of the imaging element is positioned on the imaging plane.
  • the light emitted from the eyepiece of the rigid endoscope is imaged on the imaging surface of the imaging device.
  • the exit pupil position of the imaging optical system moves on the optical axis, so that the light incident from the imaging optical system to the imaging surface
  • the incident angle formed with the optical axis of the system changes.
  • conditional expression (1) is that the imaging optical system with respect to the exit pupil position of the rigid endoscope so that the incident angle of the chief ray at the maximum image height to the imaging plane is within ⁇ 3 ° at the wide angle end. This defines the amount of deviation of the front focal position.
  • Conditional expression (2) indicates that, at the telephoto end, the front focal point of the imaging optical system with respect to the exit pupil position of the rigid endoscope so that the incident angle of the chief ray at the maximum image height to the imaging plane is within ⁇ 3 °. This defines the amount of deviation from the position.
  • the incident angle to the image plane is within ⁇ 3 ° at both the wide-angle end and the telephoto end. Therefore, when the imaging optical system of the present invention is applied to a three-plate type imaging apparatus, the change in the incident angle of the light beam from the imaging optical system to the dichroic prism, which occurs with zooming, is suppressed, and color shading is suppressed. be able to.
  • conditional expression (3) 0.18 ⁇ h / fw ⁇ 0.23
  • Conditional expression (3) defines the magnification at the wide-angle end.
  • conditional expression (4) may be satisfied.
  • ⁇ 4 is the paraxial lateral magnification of the fourth lens group.
  • the fourth lens group is a group responsible for aberration correction and adjustment of the exit pupil position.
  • ⁇ 4 is 0.3 or less, the front principal point position of the fourth lens group is too close to the object side, or the refractive power of the fourth lens group becomes too strong, and it is difficult to adjust the exit pupil position. Become. Further, since the converging action of the fourth lens group becomes too strong, it is difficult to correct aberrations. When ⁇ 4 is 1 or more, the front principal point position of the fourth lens group is too close to the image plane side, so that it is difficult to adjust the exit pupil position, and the refractive power of the other groups becomes relatively strong, resulting in aberrations. Correction becomes difficult.
  • the first lens group and the fourth lens group are fixed at the time of zooming, and at the time of zooming from the wide angle end to the telephoto end, the second lens group is moved from the object side to the image side.
  • the third lens group may move from the object side to the image side and then move from the object side to the image side.
  • FIG. 1 is an overall configuration diagram of a camera head including an imaging optical system according to an embodiment of the present invention and a rigid endoscope to which the camera head is connected. It is a whole block diagram in the wide-angle end (upper stage) and telephoto end (lower stage) of the imaging optical system which concerns on one Embodiment of this invention. It is a figure explaining conditional expression (1) and (2). It is a figure explaining the relationship between conditional expression (3) and the dimension of the endoscopic image displayed on a screen. It is a figure explaining the relationship between conditional expression (3) and the dimension of the endoscopic image displayed on a screen. It is a figure explaining the relationship between conditional expression (3) and the dimension of the endoscopic image displayed on a screen. It is a figure explaining the relationship between conditional expression (3) and the dimension of the endoscopic image displayed on a screen. FIG.
  • FIG. 2 is a lens cross-sectional view at the wide-angle end (upper stage), midway state (middle stage), and telephoto end (lower stage) of the imaging optical system according to Example 1 of the present invention.
  • FIG. 8 is a diagram illustrating various aberrations at the wide-angle end of the imaging optical system in FIG. 7.
  • FIG. 8 is a diagram of various aberrations at the telephoto end of the imaging optical system in FIG. 7.
  • FIG. 6 is a lens cross-sectional view at the wide-angle end (upper stage), halfway state (middle stage), and telephoto end (lower stage) of the imaging optical system according to Example 2 of the present invention.
  • FIG. 11 is various aberration diagrams at the wide-angle end of the imaging optical system in FIG. 10.
  • FIG. 11 is various aberration diagrams at the telephoto end of the imaging optical system in FIG. 10.
  • FIG. 6 is a lens cross-sectional view at the wide-angle end (upper stage), midway state (middle stage), and telephoto end (lower stage) of an imaging optical system according to Example 3 of the present invention.
  • FIG. 15 is a diagram illustrating various aberrations at the wide-angle end of the imaging optical system in FIG. 14.
  • FIG. 15 is a diagram of various aberrations at the telephoto end of the imaging optical system in FIG. 14.
  • an imaging optical system 1 according to an embodiment of the present invention will be described with reference to FIGS. 1 to 6.
  • the rigid endoscope 20 includes, in order from the distal end side, an objective lens 21 that forms an image of light from an object, a relay lens 22, and an eyepiece lens 23 that magnifies an image formed by the objective lens 21.
  • Light incident on the objective lens 21 from the object is relayed from the objective lens 21 to the eyepiece lens 23 by the relay lens 22 and emitted from the eyepiece lens 23 of the eyepiece portion 24 provided at the proximal end of the rigid endoscope 20.
  • the camera head 10 has a built-in imaging device for photographing the light emitted from the eyepiece lens 23.
  • the imaging apparatus forms an image of light incident on the camera head 10 from the cover glass 2 and the eyepiece 23 through the cover glass 2 in order from the distal end side (object side) to the proximal end side (image side).
  • An imaging optical system 1 and a dichroic prism 3 that divides light emitted from the imaging optical system 1 into R (red), G (green), and B (blue) light are provided.
  • the imaging apparatus includes three imaging elements 4, 5, and 6 in which imaging surfaces 4a, 5a, and 6a are respectively arranged on the imaging surfaces of the three colors of light emitted from the dichroic prism 3.
  • the camera head 10 When the camera head 10 is connected to the proximal end of the rigid endoscope 20, the camera head 10 has a body surface 2a that structurally abuts against the proximal end surface of the eyepiece portion 24 including the eyepiece lens 23.
  • the object side surface of the cover glass 2 and the body surface 2a are arranged on the same plane, but the relative position of the cover glass 2 and the body surface 2a in the optical axis direction is limited to this. It is not something.
  • the optical axis of the imaging optical system 1 In a state where the camera head 10 is connected to the rigid endoscope 20, the optical axis of the imaging optical system 1 is positioned on an extension line of the optical axis of the eyepiece lens 23.
  • the dichroic prism 3 emits the separated three colors of light in different directions.
  • the imaging surfaces 4a, 5a, and 6a are disposed at the light emission positions of the three colors, respectively. Light incident on the imaging surfaces 4a, 5a, and 6a is photoelectrically converted by the imaging elements 4, 5, and 6, respectively, and then synthesized by the image processing device 30 and displayed on the monitor 40 as a color endoscope image 9. It is like that.
  • the imaging device is not limited to a three-plate type including three imaging elements, but may be a two-plate type including two imaging elements or a single-plate type including a single imaging element.
  • the imaging optical system 1 includes, in order from the object side to the image side, a first lens group G1 having a positive refractive power, a second lens group G2 having a negative refractive power, It consists of a third lens group G3 having a positive refractive power and a fourth lens group G4 having a positive refractive power.
  • the dichroic prism 3 is simplified and only the imaging surface 5 a located on the optical axis of the imaging optical system 1 is representatively shown among the three imaging surfaces 4 a, 5 a, 6 a.
  • the imaging optical system 1 may further include an arbitrary optical element having substantially no refractive power in addition to the four lens groups G1, G2, G3, and G4.
  • the second lens group G2 and the third lens group G3 move in the optical axis direction, and the first lens group G1 and the fourth lens group G4 are fixed.
  • the first lens group G1 functions as a focusing lens that collects the light incident on the imaging optical system 1 from the eyepiece lens 23.
  • the second lens group G2 functions as a variator lens having a zoom function.
  • the second lens group G2 is provided so as to be movable on the optical axis between a wide-angle position and a telephoto position closer to the image side than the wide-angle position.
  • the imaging optical system 1 has the shortest focal length when the second lens group G2 is disposed at the wide-angle position, and has a focal length when the second lens group G2 is disposed at the telephoto position. The longest telephoto end.
  • the third lens group G3 functions as a compensator for adjusting the imaging position so that the position of the imaging surface is constant regardless of the position on the optical axis of the second lens group G2.
  • the third lens group G3 is provided so as to be movable on the optical axis and moves following the movement of the image accompanying the movement of the second lens group G2. Specifically, in the process in which the second lens group G2 moves from the wide-angle position to the telephoto position, the image formed by the second lens group G2 first moves from the object side to the image side, and then turns back to the object side. Follow the trajectory. Therefore, the third lens group G3 first moves from the object side to the image side and then moves back to the object side when zooming from the wide-angle end to the telephoto end.
  • the imaging optical system 1 satisfies the conditional expressions (1) and (2).
  • ffw is the front focal position of the imaging optical system 1 at the wide-angle end with the body-mounted surface 2a as the origin (the distance from the body-mounted surface 2a to the front focal point)
  • fw is the imaging optical system 1 at the wide-angle end.
  • the focal length, fft is the front focal position of the imaging optical system 1 at the telephoto end with the body surface 2a as the origin (distance from the body surface 2a to the front focal point), and ft is the imaging optical system 1 at the telephoto end.
  • H is the maximum image height on the imaging plane (imaging plane)
  • D is the exit pupil position of the rigid endoscope 20 with the origin of the barreled surface 2a (the distance from the barreled surface 2a to the exit pupil)
  • Ffw, fft, and D are positive in the direction from the object side (cover glass side) to the image side (imaging device side)
  • the units of ffw, fw, fft, ft, h, and D are Mm.
  • FIG. 3 is a diagram for explaining conditional expressions (1) and (2).
  • conditional expression (1) ffw ⁇ D represents the distance ⁇ between the exit pupil P of the rigid endoscope 2 and the front focal point FF at the wide-angle end of the imaging optical system 1.
  • Conditional expression (1) defines ffw ⁇ D so that the incident angle ⁇ of the principal ray R on the imaging surface (imaging surface) at the maximum image height at the wide-angle end is not less than ⁇ 3 ° and not more than + 3 °. It is.
  • conditional expression (2) fft ⁇ D represents the distance ⁇ between the exit pupil P of the rigid endoscope 2 and the front focal point FF at the telephoto end of the imaging optical system 1.
  • Conditional expression (2) defines fft-D so that the incident angle ⁇ of the principal ray R on the imaging surface (imaging surface) at the maximum image height at the telephoto end is not less than ⁇ 3 ° and not more than + 3 °. It is.
  • the exit pupil position of the imaging optical system 1 is + (right side of the imaging surface in FIG. 3) with respect to the imaging surface, the incident angle ⁇ is incident on the imaging surface as a convergent light beam.
  • the sign of is +.
  • the exit pupil position of the imaging optical system 1 is ⁇ (left side of the imaging surface in FIG. 3) with respect to the imaging surface, and the light is incident on the imaging surface as a divergent light beam, the sign of the incident angle ⁇ is ⁇ . Yes.
  • Conditional expressions (1) and (2) are derived as follows.
  • the exit pupil P position of the eyepiece lens 23 of the rigid endoscope 20 is disposed at a position protruding about 10 mm from the eyepiece lens 23, and 3 mm from the eyepiece lens 23 to the body surface 2a due to the structural restrictions of the frame. About a certain interval. Therefore, the exit pupil P position of the rigid endoscope 20 is at a position about 7 mm inside the imaging optical system 1. Since the entrance pupil position of the imaging optical system 1 is the exit pupil P position of the rigid endoscope 20, the front focal FF position of the imaging optical system 1 is set to the exit of the rigid endoscope 20 in order to configure a telecentric optical system. What is necessary is to make it coincide with the pupil P position.
  • the principal ray R emitted from the imaging optical system 1 is parallel to the optical axis of the imaging optical system 1.
  • the principal ray R emitted from the imaging optical system 1 is inclined with respect to the optical axis, as shown in FIG.
  • the light enters the dichroic prism 3 and also enters the imaging surface 4a obliquely. At this time, color shading occurs in the color endoscope image 9 acquired by the imaging elements 4, 5, and 6.
  • the front focal point FF of the imaging optical system 1 moves on the optical axis, and the front focal point FF with respect to the exit pupil P is changed.
  • the position changes.
  • the difference ⁇ in the optical axis direction between the exit pupil P position and the front focus FF position increases, the incident angle ⁇ of light on the imaging surface 4a increases and the amount of color shading increases. Therefore, in order to suppress color shading, the difference ⁇ and the incident angle ⁇ at the wide-angle end and the telephoto end may be limited.
  • the difference ⁇ is expressed by the following equation (a).
  • ⁇ (f 2 / h) tan ⁇ (a) If the incident angle ⁇ of the principal ray R on the imaging surface satisfies ⁇ 3 ° ⁇ ⁇ ⁇ + 3 ° at both the wide-angle end and the telephoto end, the wide-angle end and the telephoto end hardly change with little incidence angle ⁇ . , And the occurrence of color shading accompanying the scaling can be suppressed.
  • ⁇ 0.052 (f 2 / h) (a ′)
  • the front focal point FF position needs to satisfy the following expression (b).
  • D ⁇ ⁇ ff ⁇ D + ⁇ (b) Substituting the formula (a ′) into the formula (b), the following formula (b ′) is obtained. D ⁇ 0.052 (f 2 /h) ⁇ ff ⁇ D+0.052(f 2 / h) (b ′)
  • the formula (b ′) can be transformed into the following formula (b ′′).
  • the incident angle of the light to the dichroic prism 3 is almost changed by satisfying the conditional expressions (1) and (2). It is possible to change the magnification between the wide-angle end and the telephoto end without causing the change. Thereby, there exists an advantage that the endoscopic image 9 by which color shading was suppressed in both a wide-angle end and a telephoto end can be acquired. Further, by providing the third lens group G3 only with a function as a compensator and including the fourth lens group G4 that is fixed at the time of zooming, the refractive power of the third lens group G3 can be weakened. There is an advantage that the change of the incident angle ⁇ of the principal ray R accompanying the movement of the second lens group G2 can be effectively suppressed by the third lens group G3.
  • the imaging optical system 1 further satisfies the conditional expression (3).
  • (3) 0.18 ⁇ h / fw ⁇ 0.23
  • the endoscopic image 9 displayed on the screen 41 of the monitor 40 is provided with a mask 8 having a round opening 8a and covering the periphery of the endoscopic image 9 as shown in FIG.
  • Conditional expression (3) defines the magnification at the wide-angle end so that the entire endoscopic image 9 is displayed in an appropriate size on the screen 41 even at the wide-angle end where the magnification is large.
  • the diameter dimension of the opening 8 a of the mask 8 displayed on the screen 41 is larger than the dimension of the screen 41, and the endoscopic image 9 is partly lost and part of the endoscopic image 9 cannot be observed on the screen 41.
  • h / fw is 0.23 or more, the endoscope image 9 displayed on the screen 41 is too small to be suitable for observation.
  • the imaging optical system 1 further satisfies the conditional expression (4).
  • (4) 0.3 ⁇ 4 ⁇ 1
  • ⁇ 4 is the paraxial lateral magnification of the fourth lens group G4.
  • Conditional expression (4) defines the strength of the converging action of the fourth lens group G4.
  • the fourth lens group G4 can have an appropriate convergence function, and the fourth lens group G4 can appropriately adjust the exit pupil position of the imaging optical system 1.
  • the aberration can be corrected satisfactorily.
  • ⁇ 4 When ⁇ 4 is 0.3 or less, the front principal point position of the fourth lens group G4 is too close to the object side, or the refractive power of the fourth lens group G4 is too strong, so that the emission of the imaging optical system 1 It becomes impossible to adjust the pupil position to an appropriate position, and it becomes difficult to correct the aberration.
  • ⁇ 4 is 1 or more, the front principal point position of the fourth lens group G4 is too close to the image plane side, so that the exit pupil position of the imaging optical system 1 cannot be adjusted to an appropriate position, and other The refractive powers of the lens groups G1, G2, and G3 become relatively strong, making it difficult to correct aberrations.
  • r is a radius of curvature (mm)
  • d is a surface interval (mm)
  • n is a refractive index with respect to the d line
  • ⁇ is an Abbe number with respect to the d line.
  • the first surface (r1) is a body surface.
  • the unit of f (focal length of the entire system), ffw, fft, D, and h described in various data is mm.
  • d13 minimum indicates an intermediate state when the third lens unit is disposed closest to the image side in the process of zooming from the wide-angle end to the telephoto end.
  • reference numerals other than d5, d8 and d13 are omitted.
  • FIG. 7 shows a lens configuration diagram of the imaging optical system according to Example 1 of the present invention.
  • FIG. 8 shows various aberration diagrams at the wide-angle end
  • FIG. 9 shows various aberration diagrams at the telephoto end.
  • the lens data and various data of this example are as shown below.
  • a fourth lens group is provided on the image side of the third lens group to distribute the positive refractive power to the third lens group and the fourth lens group, thereby reducing the refractive power of the third lens group. ing.
  • FIG. 10 shows a lens configuration diagram of the imaging optical system according to Example 2 of the present invention.
  • FIG. 11 shows the movement locus of the principal point position of each lens group G1, G2, G3, G4 at the time of zooming.
  • FIG. 12 shows various aberration diagrams at the wide angle end, and
  • FIG. 13 shows various aberration diagrams at the telephoto end.
  • the lens data and various data of this example are as shown below.
  • a fourth lens group is provided on the image side of the third lens group to distribute the positive refractive power to the third lens group and the fourth lens group, thereby reducing the refractive power of the third lens group. ing.
  • the fourth lens group includes a negative lens and a positive lens in order from the object side. Thereby, the principal point position of the fourth lens group is located closer to the image plane side than the third lens group, and the incident angle of light on the imaging surface can be further reduced at the telephoto end.
  • FIG. 14 shows a lens configuration diagram of an imaging optical system according to Example 3 of the present invention.
  • FIG. 15 shows the movement locus of the principal point position of each lens group at the time of zooming.
  • FIG. 16 shows various aberration diagrams at the wide-angle end, and
  • FIG. 17 shows various aberration diagrams at the telephoto end.
  • the lens data and various data of this example are as shown below.
  • a fourth lens group is provided on the image side of the third lens group to distribute the positive refractive power to the third lens group and the fourth lens group, thereby reducing the refractive power of the third lens group. ing.
  • the fourth lens group includes a positive lens and a negative lens in order from the object side.
  • the principal point position of the fourth lens group is located closer to the object side than the third lens group, and the incident angle of light on the imaging surface can be further reduced at the wide angle end.
  • the most object-side surface (surface number 9) and the most image-side surface (surface number) 13 are flat surfaces. Can be reduced.

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Abstract

Image pickup optical system (1) has a variable magnification ratio of 1.5x or higher, comprises, in order from the object side toward the image side, a first lens group (G1) having positive refractive power, a second lens group (G2) having a negative refractive power, a third lens group (G3) having a positive refractive power, and a fourth lens group (G4) having a positive refractive power, and satisfies conditional expressions (1) and (2). In the formulas, ffw is the forward focal position at the wide-angle end with the barrel attachment surface (2a) as the origin, fw is the focal distance of the entire system at the wide-angle end, fft is the forward focal position at the telescopic end with the barrel attachment surface (2a) as the origin, ft is the focal distance of the entire system at the telescopic end, h is the maximum image height at the imaging surface (5a), and D is the exit pupil position of a rigid endoscope with the barrel attachment surface (2a) as the origin. (1) | (ffw–D) / fw2 | ≤ 0.052 /h (2) | (fft–D)/ft2| ≤ 0.052/h

Description

撮像光学系Imaging optical system
　本発明は、撮像光学系に関し、特に、硬性内視鏡用のカメラヘッドに搭載される撮像光学系に関するものである。 The present invention relates to an imaging optical system, and particularly to an imaging optical system mounted on a camera head for a rigid endoscope.
　従来、硬性内視鏡の観察像を撮影してモニタに表示するために硬性内視鏡用のカメラヘッドが使用されている。カメラヘッドは、撮像素子と、硬性内視鏡の基端に設けられた接眼レンズから射出された光を撮像素子の撮像面に結像する撮像光学系とを備え、硬性内視鏡の基端に接続して使用される。このような撮像光学系として、ズーム機能を備えたものが知られている（例えば、特許文献１および２参照。）。 Conventionally, a camera head for a rigid endoscope has been used to shoot an observation image of a rigid endoscope and display it on a monitor. The camera head includes an imaging element and an imaging optical system that forms an image on the imaging surface of the imaging element with light emitted from an eyepiece provided at the proximal end of the rigid endoscope, and the proximal end of the rigid endoscope Used in connection with. As such an imaging optical system, one having a zoom function is known (see, for example, Patent Documents 1 and 2).
　一方、近年、内視鏡用の撮像装置として、画質および色再現性に優れた３板式の撮像装置が使用されることが多くなってきている。３板式の撮像装置は、入射光をＲ、Ｇ、Ｂの３色の光に分割するダイクロイックプリズムと、該ダイクロイックプリズムによって分割された３色の光を撮影する３個の撮像素子とを備えている。 On the other hand, in recent years, a three-plate type imaging device excellent in image quality and color reproducibility is often used as an imaging device for an endoscope. The three-plate type imaging device includes a dichroic prism that divides incident light into light of three colors of R, G, and B, and three imaging elements that photograph three colors of light divided by the dichroic prism. Yes.
特開平１１－１２５７７０号公報Japanese Patent Laid-Open No. 11-125770 特許第４０４３５８７号公報Japanese Patent No. 4043587
　しかしながら、特許文献１，２に記載の撮像光学系は、３板式の撮像装置に適用したときに、変倍に伴って発生する色シェーディングを抑制することが難しいという問題がある。すなわち、硬性内視鏡に内視鏡用カメラヘッドを接続した状態において、硬性内視鏡の射出瞳位置が撮像光学系の入射瞳位置となる。したがって、撮像光学系によって変倍したときに、撮像光学系の入射瞳位置は一定であり、撮像光学系の射出瞳位置が移動する。この撮像光学系の射出瞳位置の移動に伴って、撮像光学系からダイクロイックプリズムへ入射する光線の入射角が変化し、光線が光軸に対して傾いてダイクロイックプリズムへ入射する。 However, the imaging optical systems described in Patent Documents 1 and 2 have a problem that it is difficult to suppress color shading that occurs with zooming when applied to a three-plate imaging apparatus. That is, in the state where the endoscope camera head is connected to the rigid endoscope, the exit pupil position of the rigid endoscope becomes the entrance pupil position of the imaging optical system. Therefore, when zooming is performed by the imaging optical system, the entrance pupil position of the imaging optical system is constant, and the exit pupil position of the imaging optical system moves. As the exit pupil position of the imaging optical system moves, the incident angle of the light beam incident on the dichroic prism from the imaging optical system changes, and the light beam is incident on the dichroic prism with an inclination with respect to the optical axis.
　ダイクロイックプリズムは、入射光を３色の光に分解するために、特定の波長の光を選択的に透過させて他の波長の光を反射する多層干渉膜からなる反射面を有する。反射面への光線の入射角が変化すると、多層干渉膜の内部における光線の光路長が変化するため、反射面の透過波長が変化する。したがって、撮像光学系からダイクロイックプリズムへの光線の入射角が変倍に伴って傾くと、ダイクロイックプリズムから射出される光の色も変化し、その結果、モニタに表示される内視鏡画像には、上部と下部とで色が異なる色シェーディングが垂直方向に発生する。 The dichroic prism has a reflecting surface made of a multilayer interference film that selectively transmits light of a specific wavelength and reflects light of other wavelengths in order to decompose incident light into three colors of light. When the incident angle of the light beam on the reflecting surface changes, the optical path length of the light beam inside the multilayer interference film changes, so that the transmission wavelength of the reflecting surface changes. Therefore, when the incident angle of the light beam from the imaging optical system to the dichroic prism is tilted with magnification, the color of the light emitted from the dichroic prism also changes, and as a result, the endoscopic image displayed on the monitor Color shading with different colors at the top and bottom occurs in the vertical direction.
　撮像光学系の変倍比が大きい程、変倍時の射出瞳位置の移動量が大きくなるため、色シェーディングの発生量も大きくなる。特許文献１，２には大きな変倍比を有する撮像光学系が開示されているが、これらの撮像光学系は変倍時の射出瞳位置の移動量が大きいため、３板式の撮像装置と組み合わせたときに、ダイクロイックプリズムへの光線の入射角の変化を抑制することができず、色シェーディングを抑制することができない。 The greater the magnification ratio of the imaging optical system, the greater the amount of movement of the exit pupil position during zooming, and the greater the amount of color shading. Patent Documents 1 and 2 disclose imaging optical systems having a large zoom ratio, but these imaging optical systems have a large amount of movement of the exit pupil position at the time of zooming, so they are combined with a three-plate imaging device. The change in the incident angle of the light beam to the dichroic prism cannot be suppressed, and the color shading cannot be suppressed.
　本発明は、上述した事情に鑑みてなされたものであって、大きな変倍比を有しつつ変倍時の色シェーディングを抑制することができる撮像光学系を提供することを目的とする。 The present invention has been made in view of the above-described circumstances, and an object thereof is to provide an imaging optical system that can suppress color shading during zooming while having a large zoom ratio.
　上記目的を達成するため、本発明は以下の手段を提供する。
　本発明は、硬性内視鏡の接眼レンズを含むアイピース部の基端面に胴付面が突き当たるように前記硬性内視鏡の基端に接続されるカメラヘッドに内蔵され、前記接眼レンズから入射した光を結像する撮像光学系であって、広角端と望遠端との間で変倍可能であり、１．５倍以上の変倍比を有するとともに、物体側から像側へ向かって順に、正の屈折力を有する第１レンズ群と、負の屈折力を有する第２レンズ群と、正の屈折力を有する第３レンズ群と、正の屈折力を有する第４レンズ群とからなり、下記の条件式（１）および（２）満足する撮像光学系を提供する。
（１）　　　　｜（ｆｆｗ－Ｄ）／ｆｗ２｜　≦　０．０５２／ｈ
（２）　　　　｜（ｆｆｔ－Ｄ）／ｆｔ２｜　≦　０．０５２／ｈ
　ただし、ｆｆｗは、前記胴付面を原点とした広角端での前記撮像光学系の前側焦点位置、ｆｗは、広角端における前記撮像光学系の全系の焦点距離、ｆｆｔは、前記胴付面を原点とした望遠端での前記撮像光学系の前側焦点位置、ｆｔは、望遠端における前記撮像光学系の全系の焦点距離、ｈは、前記撮像光学系の結像面における最大像高、Ｄは、前記胴付面を原点とした前記硬性内視鏡の射出瞳位置であり、物体側から像側へ向かう光軸方向を正とする。 In order to achieve the above object, the present invention provides the following means.
The present invention is incorporated in the camera head connected to the proximal end of the rigid endoscope so that the body-mounted surface abuts the proximal end surface of the eyepiece part including the eyepiece of the rigid endoscope, and is incident from the eyepiece An imaging optical system that forms an image of light, which can be zoomed between the wide-angle end and the telephoto end, has a zoom ratio of 1.5 times or more, and in order from the object side to the image side, A first lens group having a positive refractive power; a second lens group having a negative refractive power; a third lens group having a positive refractive power; and a fourth lens group having a positive refractive power; An imaging optical system that satisfies the following conditional expressions (1) and (2) is provided.
(1) | (ffw−D) / fw 2 | ≦ 0.052 / h
(2) | (fft−D) / ft 2 | ≦ 0.052 / h
Where ffw is the front focal position of the imaging optical system at the wide-angle end with the body-mounted surface as the origin, fw is the focal length of the entire system of the imaging optical system at the wide-angle end, and fft is the body-mounted surface Is the front focal position of the imaging optical system at the telephoto end with the origin as the origin, ft is the focal length of the entire system of the imaging optical system at the telephoto end, h is the maximum image height on the imaging plane of the imaging optical system, D is the exit pupil position of the rigid endoscope with the torso surface as the origin, and the optical axis direction from the object side to the image side is positive.
　本発明の撮像光学系は、物体側に硬性内視鏡が位置し、結像面に撮像素子の撮像面が位置するように、硬性内視鏡と撮像素子との間に配置して使用され、硬性内視鏡の接眼レンズから射出された光を撮像素子の撮像面に結像する。
　この場合に、広角端と望遠端との間で変倍したときに、撮像光学系の射出瞳位置が光軸上を移動することによって、撮像光学系から結像面へ入射する光線が撮像光学系の光軸と成す入射角が変化する。 The imaging optical system of the present invention is used by being disposed between the rigid endoscope and the imaging element so that the rigid endoscope is positioned on the object side and the imaging surface of the imaging element is positioned on the imaging plane. The light emitted from the eyepiece of the rigid endoscope is imaged on the imaging surface of the imaging device.
In this case, when the magnification is changed between the wide-angle end and the telephoto end, the exit pupil position of the imaging optical system moves on the optical axis, so that the light incident from the imaging optical system to the imaging surface The incident angle formed with the optical axis of the system changes.
　ここで、条件式（１）は、広角端において、最大像高における主光線の結像面への入射角が±３°以内となるように、硬性内視鏡の射出瞳位置に対する撮像光学系の前側焦点位置のずれ量を規定したものである。条件式（２）は、望遠端において、最大像高における主光線の結像面への入射角が±３°以内となるように、硬性内視鏡の射出瞳位置に対する撮像光学系の前側焦点位置とのずれ量を規定したものである。 Here, the conditional expression (1) is that the imaging optical system with respect to the exit pupil position of the rigid endoscope so that the incident angle of the chief ray at the maximum image height to the imaging plane is within ± 3 ° at the wide angle end. This defines the amount of deviation of the front focal position. Conditional expression (2) indicates that, at the telephoto end, the front focal point of the imaging optical system with respect to the exit pupil position of the rigid endoscope so that the incident angle of the chief ray at the maximum image height to the imaging plane is within ± 3 °. This defines the amount of deviation from the position.
　条件式（１）および（２）を満足することによって、広角端および望遠端の両方において、結像面への入射角は±３°以内となる。したがって、本発明の撮像光学系を３板式の撮像装置に適用した場合に、変倍に伴って生じる、撮像光学系からダイクロイックプリズムへの光線の入射角の変化を抑制し、色シェーディングを抑制することができる。 By satisfying conditional expressions (1) and (2), the incident angle to the image plane is within ± 3 ° at both the wide-angle end and the telephoto end. Therefore, when the imaging optical system of the present invention is applied to a three-plate type imaging apparatus, the change in the incident angle of the light beam from the imaging optical system to the dichroic prism, which occurs with zooming, is suppressed, and color shading is suppressed. be able to.
　上記発明においては、下記の条件式（３）を満足していてもよい。
（３）　　　　０．１８　＜　ｈ／ｆｗ　＜　０．２３
　条件式（３）は、広角端における倍率を規定したものである。条件式（３）を満足することによって、撮像素子によって取得された内視鏡画像の全体をモニタの画面上に適切な大きさで表示することができる。ｈ／ｆｗが０．１８以下である場合、画面における内視鏡画像の寸法が大きくなり、内視鏡画像の端部が画面からはみ出してしまう可能性がある。ｈ／ｆｗが０．２３以上である場合、画面に対して内視鏡画像が小さ過ぎて観察に適さない。 In the said invention, the following conditional expression (3) may be satisfied.
(3) 0.18 <h / fw <0.23
Conditional expression (3) defines the magnification at the wide-angle end. By satisfying conditional expression (3), the entire endoscopic image acquired by the image sensor can be displayed on the monitor screen in an appropriate size. When h / fw is 0.18 or less, the size of the endoscopic image on the screen becomes large, and the end portion of the endoscopic image may protrude from the screen. When h / fw is 0.23 or more, the endoscopic image is too small for the screen and is not suitable for observation.
　上記発明においては、下記の条件式（４）を満足してもよい。
（４）　　　　０．３　＜　β４　＜　１
　ただし、β４は、第４レンズ群の近軸横倍率である。
　第４レンズ群は、収差補正および射出瞳位置の調整を担う群である。条件式（４）を満足することで、第４レンズ群が有する収斂作用の強さが適切となり、収差を良好に補正し、かつ、射出瞳位置を適切に調整することができる。 In the above invention, the following conditional expression (4) may be satisfied.
(4) 0.3 <β4 <1
Where β4 is the paraxial lateral magnification of the fourth lens group.
The fourth lens group is a group responsible for aberration correction and adjustment of the exit pupil position. By satisfying conditional expression (4), the strength of the convergence action of the fourth lens group becomes appropriate, aberrations can be corrected well, and the exit pupil position can be adjusted appropriately.
　β４が０．３以下である場合、第４レンズ群の前側主点位置が物体側に寄り過ぎるか、または、第４レンズ群の屈折力が強くなり過ぎるため、射出瞳位置の調整が困難となる。さらに、第４レンズ群の収斂作用が強くなり過ぎるため、収差の補正が困難となる。β４が１以上である場合、第４レンズ群の前側主点位置が像面側に寄り過ぎるため、射出瞳位置の調整が困難となり、さらに他の群の屈折力が相対的に強くなって収差の補正が困難となる。 If β4 is 0.3 or less, the front principal point position of the fourth lens group is too close to the object side, or the refractive power of the fourth lens group becomes too strong, and it is difficult to adjust the exit pupil position. Become. Further, since the converging action of the fourth lens group becomes too strong, it is difficult to correct aberrations. When β4 is 1 or more, the front principal point position of the fourth lens group is too close to the image plane side, so that it is difficult to adjust the exit pupil position, and the refractive power of the other groups becomes relatively strong, resulting in aberrations. Correction becomes difficult.
　上記発明においては、前記第１レンズ群および前記第４レンズ群が、変倍時に固定であり、前記広角端から前記望遠端への変倍時に、前記第２レンズ群が、物体側から像側へ一方向に移動し、前記第３レンズ群が、物体側から像側へ移動し、その後に物体側から像側へ移動してもよい。
　第２レンズ群および第３レンズ群の両方の近軸横倍率が等倍である場合、変倍時の入射角の変動を抑制することが難しい。そこで、第２レンズ群の近軸横倍率を等倍とし、第３レンズ群をコンペンセータとして機能させることによって、変倍時の入射角の変動をさらに効果的に抑制することができる。 In the above invention, the first lens group and the fourth lens group are fixed at the time of zooming, and at the time of zooming from the wide angle end to the telephoto end, the second lens group is moved from the object side to the image side. The third lens group may move from the object side to the image side and then move from the object side to the image side.
When the paraxial lateral magnifications of both the second lens group and the third lens group are equal, it is difficult to suppress the change in the incident angle at the time of zooming. Therefore, by changing the paraxial lateral magnification of the second lens group to the same magnification and causing the third lens group to function as a compensator, it is possible to more effectively suppress the variation in the incident angle during zooming.
　本発明によれば、大きな変倍比を有しつつ変倍時の色シェーディングを抑制することができるという効果を奏する。 According to the present invention, there is an effect that color shading at the time of zooming can be suppressed while having a large zoom ratio.
本発明の一実施形態に係る撮像光学系を備えるカメラヘッドと、該カメラヘッドが接続される硬性内視鏡の全体構成図である。1 is an overall configuration diagram of a camera head including an imaging optical system according to an embodiment of the present invention and a rigid endoscope to which the camera head is connected. 本発明の一実施形態に係る撮像光学系の広角端（上段）および望遠端（下段）における全体構成図である。It is a whole block diagram in the wide-angle end (upper stage) and telephoto end (lower stage) of the imaging optical system which concerns on one Embodiment of this invention. 条件式（１）および（２）を説明する図である。It is a figure explaining conditional expression (1) and (2). 条件式（３）と、画面に表示される内視鏡画像の寸法との関係を説明する図である。It is a figure explaining the relationship between conditional expression (3) and the dimension of the endoscopic image displayed on a screen. 条件式（３）と、画面に表示される内視鏡画像の寸法との関係を説明する図である。It is a figure explaining the relationship between conditional expression (3) and the dimension of the endoscopic image displayed on a screen. 条件式（３）と、画面に表示される内視鏡画像の寸法との関係を説明する図である。It is a figure explaining the relationship between conditional expression (3) and the dimension of the endoscopic image displayed on a screen. 本発明の実施例１に係る撮像光学系の広角端（上段）、途中状態（中段）および望遠端（下段）におけるレンズ断面図である。FIG. 2 is a lens cross-sectional view at the wide-angle end (upper stage), midway state (middle stage), and telephoto end (lower stage) of the imaging optical system according to Example 1 of the present invention. 図７の撮像光学系の広角端における各種収差図である。FIG. 8 is a diagram illustrating various aberrations at the wide-angle end of the imaging optical system in FIG. 7. 図７の撮像光学系の望遠端における各種収差図である。FIG. 8 is a diagram of various aberrations at the telephoto end of the imaging optical system in FIG. 7. 本発明の実施例２に係る撮像光学系の広角端（上段）、途中状態（中段）および望遠端（下段）におけるレンズ断面図である。FIG. 6 is a lens cross-sectional view at the wide-angle end (upper stage), halfway state (middle stage), and telephoto end (lower stage) of the imaging optical system according to Example 2 of the present invention. 図１０の撮像光学系の広角端（上段）、途中状態（中段）および望遠端（下段）における各レンズ群の主点位置を示す図である。It is a figure which shows the principal point position of each lens group in the wide-angle end (upper stage), middle state (middle stage), and telephoto end (lower stage) of the imaging optical system of FIG. 図１０の撮像光学系の広角端における各種収差図である。FIG. 11 is various aberration diagrams at the wide-angle end of the imaging optical system in FIG. 10. 図１０の撮像光学系の望遠端における各種収差図である。FIG. 11 is various aberration diagrams at the telephoto end of the imaging optical system in FIG. 10. 本発明の実施例３に係る撮像光学系の広角端（上段）、途中状態（中段）および望遠端（下段）におけるレンズ断面図である。FIG. 6 is a lens cross-sectional view at the wide-angle end (upper stage), midway state (middle stage), and telephoto end (lower stage) of an imaging optical system according to Example 3 of the present invention. 図１４の撮像光学系の広角端（上段）、途中状態（中段）および望遠端（下段）における各レンズ群の主点位置を示す図である。It is a figure which shows the principal point position of each lens group in the wide-angle end (upper stage), middle state (middle stage), and telephoto end (lower stage) of the imaging optical system of FIG. 図１４の撮像光学系の広角端における各種収差図である。FIG. 15 is a diagram illustrating various aberrations at the wide-angle end of the imaging optical system in FIG. 14. 図１４の撮像光学系の望遠端における各種収差図である。FIG. 15 is a diagram of various aberrations at the telephoto end of the imaging optical system in FIG. 14.
　以下に、本発明の一実施形態に係る撮像光学系１について図１から図６を参照して説明する。
　まず、本実施形態の撮像光学系１が搭載されるカメラヘッド１０および該カメラヘッド１０が適用される硬性内視鏡２０の概要について説明する。カメラヘッド１０は、図１に示されるように、硬性内視鏡２０の基端に接続して使用されるものである。硬性内視鏡２０は、先端側から順に、物体からの光を結像する対物レンズ２１と、リレーレンズ２２と、対物レンズ２１によって形成された像を拡大する接眼レンズ２３とを備えている。物体から対物レンズ２１に入射した光は、リレーレンズ２２によって対物レンズ２１から接眼レンズ２３までリレーされ、硬性内視鏡２０の基端に設けられたアイピース部２４の接眼レンズ２３から射出される。 Hereinafter, an imaging optical system 1 according to an embodiment of the present invention will be described with reference to FIGS. 1 to 6.
First, an outline of a camera head 10 on which the imaging optical system 1 of the present embodiment is mounted and a rigid endoscope 20 to which the camera head 10 is applied will be described. As shown in FIG. 1, the camera head 10 is used by being connected to the proximal end of the rigid endoscope 20. The rigid endoscope 20 includes, in order from the distal end side, an objective lens 21 that forms an image of light from an object, a relay lens 22, and an eyepiece lens 23 that magnifies an image formed by the objective lens 21. Light incident on the objective lens 21 from the object is relayed from the objective lens 21 to the eyepiece lens 23 by the relay lens 22 and emitted from the eyepiece lens 23 of the eyepiece portion 24 provided at the proximal end of the rigid endoscope 20.
　カメラヘッド１０には、接眼レンズ２３から射出された光を撮影するための撮像装置が内蔵されている。撮像装置は、先端側（物体側）から基端側（像側）へ向かって順に、カバーガラス２と、接眼レンズ２３からカバーガラス２を介してカメラヘッド１０内に入射した光を結像させる撮像光学系１と、該撮像光学系１から射出された光をＲ（赤）、Ｇ（緑）およびＢ（青）の光に分割するダイクロイックプリズム３とを備えている。さらに、撮像装置は、ダイクロイックプリズム３から射出された３色の光の結像面に撮像面４ａ，５ａ，６ａがそれぞれ配置された３個の撮像素子４，５，６を備えている。 The camera head 10 has a built-in imaging device for photographing the light emitted from the eyepiece lens 23. The imaging apparatus forms an image of light incident on the camera head 10 from the cover glass 2 and the eyepiece 23 through the cover glass 2 in order from the distal end side (object side) to the proximal end side (image side). An imaging optical system 1 and a dichroic prism 3 that divides light emitted from the imaging optical system 1 into R (red), G (green), and B (blue) light are provided. Furthermore, the imaging apparatus includes three imaging elements 4, 5, and 6 in which imaging surfaces 4a, 5a, and 6a are respectively arranged on the imaging surfaces of the three colors of light emitted from the dichroic prism 3.
　カメラヘッド１０は、硬性内視鏡２０の基端に接続される際に、接眼レンズ２３を含むアイピース部２４の基端面と構造的に突き当たる胴付面２ａを有している。本実施形態においては、カバーガラス２の物体側面と胴付面２ａとが同一平面上に配置されているが、カバーガラス２と胴付面２ａとの光軸方向の相対位置はこれに限定されるものではない。カメラヘッド１０が硬性内視鏡２０に接続された状態において、撮像光学系１の光軸は、接眼レンズ２３の光軸の延長線上に位置するようになっている。 When the camera head 10 is connected to the proximal end of the rigid endoscope 20, the camera head 10 has a body surface 2a that structurally abuts against the proximal end surface of the eyepiece portion 24 including the eyepiece lens 23. In the present embodiment, the object side surface of the cover glass 2 and the body surface 2a are arranged on the same plane, but the relative position of the cover glass 2 and the body surface 2a in the optical axis direction is limited to this. It is not something. In a state where the camera head 10 is connected to the rigid endoscope 20, the optical axis of the imaging optical system 1 is positioned on an extension line of the optical axis of the eyepiece lens 23.
　ダイクロイックプリズム３は、分解した３色の光を互いに異なる方向に射出する。撮像面４ａ，５ａ，６ａは、３色の光の射出位置にそれぞれ配置されている。撮像面４ａ，５ａ，６ａに入射した光は、撮像素子４，５，６によってそれぞれ光電変換された後、画像処理装置３０において合成されてカラーの内視鏡画像９としてモニタ４０に表示されるようになっている。
　なお、撮像装置は、３個の撮像素子を備える３板式に限定されるものではなく、２個の撮像素子を備える２板式、または、単一の撮像素子を備える単板式であってもよい。 The dichroic prism 3 emits the separated three colors of light in different directions. The imaging surfaces 4a, 5a, and 6a are disposed at the light emission positions of the three colors, respectively. Light incident on the imaging surfaces 4a, 5a, and 6a is photoelectrically converted by the imaging elements 4, 5, and 6, respectively, and then synthesized by the image processing device 30 and displayed on the monitor 40 as a color endoscope image 9. It is like that.
The imaging device is not limited to a three-plate type including three imaging elements, but may be a two-plate type including two imaging elements or a single-plate type including a single imaging element.
　次に、本実施形態に係る撮像光学系１について説明する。
　撮像光学系１は、図２に示されるように、物体側から像側へ向かって順に、正の屈折力を有する第１レンズ群Ｇ１と、負の屈折力を有する第２レンズ群Ｇ２と、正の屈折力を有する第３レンズ群Ｇ３と、正の屈折力を有する第４レンズ群Ｇ４とからなる。図２において、ダイクロイックプリズム３は簡略化して示し、３つの撮像面４ａ，５ａ，６ａのうち、撮像光学系１の光軸上に位置する撮像面５ａのみを代表して示している。撮像光学系１は、４個のレンズ群Ｇ１，Ｇ２，Ｇ３，Ｇ４に加えて、実質的に屈折力を有さない任意の光学素子をさらに備えていてもよい。 Next, the imaging optical system 1 according to the present embodiment will be described.
As shown in FIG. 2, the imaging optical system 1 includes, in order from the object side to the image side, a first lens group G1 having a positive refractive power, a second lens group G2 having a negative refractive power, It consists of a third lens group G3 having a positive refractive power and a fourth lens group G4 having a positive refractive power. In FIG. 2, the dichroic prism 3 is simplified and only the imaging surface 5 a located on the optical axis of the imaging optical system 1 is representatively shown among the three imaging surfaces 4 a, 5 a, 6 a. The imaging optical system 1 may further include an arbitrary optical element having substantially no refractive power in addition to the four lens groups G1, G2, G3, and G4.
　撮像光学系１は、広角端と望遠端との間で変倍するズーム機能を有し、１．５倍以上の変倍比（＝望遠端における全系の焦点距離ｆｔ／広角端における全系の焦点距離ｆｗ）を有している。変倍の際に、第２レンズ群Ｇ２および第３レンズ群Ｇ３が光軸方向に移動し、第１レンズ群Ｇ１および第４レンズ群Ｇ４は固定である。 The imaging optical system 1 has a zoom function that varies between the wide-angle end and the telephoto end, and has a magnification ratio of 1.5 or more (= the focal length ft of the entire system at the telephoto end / the entire system at the wide-angle end) Focal length fw). During zooming, the second lens group G2 and the third lens group G3 move in the optical axis direction, and the first lens group G1 and the fourth lens group G4 are fixed.
　第１レンズ群Ｇ１は、接眼レンズ２３から撮像光学系１に入射した光を集光させるフォーカシングレンズとして機能する。
　第２レンズ群Ｇ２は、変倍機能を担うバリエータレンズとして機能する。第２レンズ群Ｇ２は、広角位置と、該広角位置よりも像側の望遠位置との間で光軸上を移動可能に設けられている。撮像光学系１は、第２レンズ群Ｇ２が広角位置に配置されているときに、焦点距離が最も短い広角端となり、第２レンズ群Ｇ２が望遠位置に配置されているときに、焦点距離が最も長い望遠端となる。 The first lens group G1 functions as a focusing lens that collects the light incident on the imaging optical system 1 from the eyepiece lens 23.
The second lens group G2 functions as a variator lens having a zoom function. The second lens group G2 is provided so as to be movable on the optical axis between a wide-angle position and a telephoto position closer to the image side than the wide-angle position. The imaging optical system 1 has the shortest focal length when the second lens group G2 is disposed at the wide-angle position, and has a focal length when the second lens group G2 is disposed at the telephoto position. The longest telephoto end.
　第３レンズ群Ｇ３は、第２レンズ群Ｇ２の光軸上の位置によらずに結像面の位置が一定となるように、結像位置を調整するためのコンペンセータとして機能する。第３レンズ群Ｇ３は、光軸上を移動可能に設けられており、第２レンズ群Ｇ２の移動に伴う像の移動に追従して移動する。具体的には、第２レンズ群Ｇ２が広角位置から望遠位置に移動する過程において、第２レンズ群Ｇ２が形成する像は、まず、物体側から像側へ移動し、その後に物体側へ折り返すような軌跡を辿る。したがって、第３レンズ群Ｇ３は、広角端から望遠端に変倍する際に、まずは物体側から像側へ移動し、その後に物体側へ折り返すように移動する。 The third lens group G3 functions as a compensator for adjusting the imaging position so that the position of the imaging surface is constant regardless of the position on the optical axis of the second lens group G2. The third lens group G3 is provided so as to be movable on the optical axis and moves following the movement of the image accompanying the movement of the second lens group G2. Specifically, in the process in which the second lens group G2 moves from the wide-angle position to the telephoto position, the image formed by the second lens group G2 first moves from the object side to the image side, and then turns back to the object side. Follow the trajectory. Therefore, the third lens group G3 first moves from the object side to the image side and then moves back to the object side when zooming from the wide-angle end to the telephoto end.
　撮像光学系１は、条件式（１）および（２）を満足している。
（１）　　　　｜（ｆｆｗ－Ｄ）／ｆｗ２｜　≦　０．０５２／ｈ
（２）　　　　｜（ｆｆｔ－Ｄ）／ｆｔ２｜　≦　０．０５２／ｈ
　ただし、ｆｆｗは、胴付面２ａを原点とした広角端での撮像光学系１の前側焦点位置（（胴付面２ａから前側焦点までの距離）、ｆｗは、広角端における撮像光学系１の焦点距離、ｆｆｔは、胴付面２ａを原点とした望遠端での撮像光学系１の前側焦点位置（胴付面２ａから前側焦点までの距離）、ｆｔは、望遠端での撮像光学系１の焦点距離、ｈは、結像面（撮像面）における最大像高、Ｄは、胴付面２ａを原点とした硬性内視鏡２０の射出瞳位置（胴付面２ａから射出瞳までの距離）である。ｆｆｗ、ｆｆｔおよびＤは、物体側（カバーガラス側）から像側（撮像素子側）へ向かう方向を正としている。また、ｆｆｗ、ｆｗ、ｆｆｔ、ｆｔ、ｈおよびＤの単位は、ｍｍである。 The imaging optical system 1 satisfies the conditional expressions (1) and (2).
(1) | (ffw−D) / fw 2 | ≦ 0.052 / h
(2) | (fft−D) / ft 2 | ≦ 0.052 / h
Here, ffw is the front focal position of the imaging optical system 1 at the wide-angle end with the body-mounted surface 2a as the origin (the distance from the body-mounted surface 2a to the front focal point), and fw is the imaging optical system 1 at the wide-angle end. The focal length, fft is the front focal position of the imaging optical system 1 at the telephoto end with the body surface 2a as the origin (distance from the body surface 2a to the front focal point), and ft is the imaging optical system 1 at the telephoto end. , H is the maximum image height on the imaging plane (imaging plane), D is the exit pupil position of the rigid endoscope 20 with the origin of the barreled surface 2a (the distance from the barreled surface 2a to the exit pupil) Ffw, fft, and D are positive in the direction from the object side (cover glass side) to the image side (imaging device side), and the units of ffw, fw, fft, ft, h, and D are Mm.
　図３は、条件式（１）および（２）を説明する図である。条件式（１）において、ｆｆｗ－Ｄは、硬性内視鏡２の射出瞳Ｐと撮像光学系１の広角端における前側焦点ＦＦとの間の距離Δを表している。条件式（１）は、広角端において最大像高における主光線Ｒの撮像面（結像面）への入射角θが－３°以上＋３°以下となるように、ｆｆｗ－Ｄを規定したものである。条件式（２）において、ｆｆｔ－Ｄは、硬性内視鏡２の射出瞳Ｐと撮像光学系１の望遠端における前側焦点ＦＦとの間の距離Δを表している。条件式（２）は、望遠端において最大像高における主光線Ｒの撮像面（結像面）への入射角θが－３°以上＋３°以下となるように、ｆｆｔ－Ｄを規定したものである。 FIG. 3 is a diagram for explaining conditional expressions (1) and (2). In conditional expression (1), ffw−D represents the distance Δ between the exit pupil P of the rigid endoscope 2 and the front focal point FF at the wide-angle end of the imaging optical system 1. Conditional expression (1) defines ffw−D so that the incident angle θ of the principal ray R on the imaging surface (imaging surface) at the maximum image height at the wide-angle end is not less than −3 ° and not more than + 3 °. It is. In conditional expression (2), fft−D represents the distance Δ between the exit pupil P of the rigid endoscope 2 and the front focal point FF at the telephoto end of the imaging optical system 1. Conditional expression (2) defines fft-D so that the incident angle θ of the principal ray R on the imaging surface (imaging surface) at the maximum image height at the telephoto end is not less than −3 ° and not more than + 3 °. It is.
　入射角θの符号に関して、撮像光学系１の射出瞳位置が撮像面に対して＋（図３において撮像面よりも右側）であり撮像面に光が収束光束として入射する場合に、入射角θの符号を＋としている。一方、撮像光学系１の射出瞳位置が撮像面に対して－（図３において撮像面よりも左側）であり撮像面に光が発散光束として入射する場合に、入射角θの符号を－としている。 Regarding the sign of the incident angle θ, when the exit pupil position of the imaging optical system 1 is + (right side of the imaging surface in FIG. 3) with respect to the imaging surface, the incident angle θ is incident on the imaging surface as a convergent light beam. The sign of is +. On the other hand, when the exit pupil position of the imaging optical system 1 is − (left side of the imaging surface in FIG. 3) with respect to the imaging surface, and the light is incident on the imaging surface as a divergent light beam, the sign of the incident angle θ is −. Yes.
　条件式（１）および（２）は、以下のようにして導かれる。
　一般に、硬性内視鏡２０の接眼レンズ２３の射出瞳Ｐ位置は、接眼レンズ２３よりも１０ｍｍ程突出した位置に配され、枠の構造上の制約から接眼レンズ２３から胴付面２ａまでは３ｍｍ程度の間隔が空く。そのため、硬性内視鏡２０の射出瞳Ｐ位置は撮像光学系１の内部に７ｍｍ程入った位置にある。撮像光学系１の入射瞳位置は硬性内視鏡２０の射出瞳Ｐ位置となるため、テレセントリック光学系を構成するためには、撮像光学系１の前側焦点ＦＦ位置を硬性内視鏡２０の射出瞳Ｐ位置と一致させればよい。 Conditional expressions (1) and (2) are derived as follows.
In general, the exit pupil P position of the eyepiece lens 23 of the rigid endoscope 20 is disposed at a position protruding about 10 mm from the eyepiece lens 23, and 3 mm from the eyepiece lens 23 to the body surface 2a due to the structural restrictions of the frame. About a certain interval. Therefore, the exit pupil P position of the rigid endoscope 20 is at a position about 7 mm inside the imaging optical system 1. Since the entrance pupil position of the imaging optical system 1 is the exit pupil P position of the rigid endoscope 20, the front focal FF position of the imaging optical system 1 is set to the exit of the rigid endoscope 20 in order to configure a telecentric optical system. What is necessary is to make it coincide with the pupil P position.
　撮像光学系１の前側焦点ＦＦ位置が硬性内視鏡２０の射出瞳Ｐ位置と一致しているときには、撮像光学系１から射出された主光線Ｒは、撮像光学系１の光軸に平行にダイクロイックプリズム３へ沿って入射し、撮像面４ａに垂直に入射する（すなわち、入射角θ＝０°である。）。一方、撮像光学系１の前側焦点ＦＦ位置が射出瞳Ｐ位置からずれているときには、図３に示されるように、撮像光学系１から射出された主光線Ｒは、光軸に対して斜めにダイクロイックプリズム３に入射し、撮像面４ａにも斜めに入射する。このときに、撮像素子４，５，６によって取得されたカラーの内視鏡画像９には色シェーディングが発生する。 When the front focal point FF position of the imaging optical system 1 coincides with the exit pupil P position of the rigid endoscope 20, the principal ray R emitted from the imaging optical system 1 is parallel to the optical axis of the imaging optical system 1. The light enters along the dichroic prism 3 and enters the imaging surface 4a perpendicularly (that is, the incident angle θ = 0 °). On the other hand, when the front focal point FF position of the imaging optical system 1 is deviated from the exit pupil P position, the principal ray R emitted from the imaging optical system 1 is inclined with respect to the optical axis, as shown in FIG. The light enters the dichroic prism 3 and also enters the imaging surface 4a obliquely. At this time, color shading occurs in the color endoscope image 9 acquired by the imaging elements 4, 5, and 6.
　ここで、第２レンズ群Ｇ２の移動によって広角端と望遠端との間で変倍する際に、撮像光学系１の前側焦点ＦＦが光軸上を移動し、射出瞳Ｐに対する前側焦点ＦＦの位置が変化する。そして、射出瞳Ｐ位置と前側焦点ＦＦ位置との光軸方向の差Δが大きくなると、撮像面４ａへの光の入射角θが大きくなり、色シェーディングの発生量も大きくなる。したがって、色シェーディングを抑制するためには、広角端および望遠端における差Δおよび入射角θを制限すればよい。 Here, when the magnification is changed between the wide-angle end and the telephoto end by the movement of the second lens group G2, the front focal point FF of the imaging optical system 1 moves on the optical axis, and the front focal point FF with respect to the exit pupil P is changed. The position changes. When the difference Δ in the optical axis direction between the exit pupil P position and the front focus FF position increases, the incident angle θ of light on the imaging surface 4a increases and the amount of color shading increases. Therefore, in order to suppress color shading, the difference Δ and the incident angle θ at the wide-angle end and the telephoto end may be limited.
　図３において、差Δは下式（ａ）で表される。
　Δ＝（ｆ２／ｈ）ｔａｎθ　・・・（ａ）
　広角端および望遠端の両方において、主光線Ｒの撮像面への入射角θが－３°≦θ≦＋３°を満足すれば、入射角θの変動をほとんど生じることなく広角端と望遠端との間で変倍することができ、変倍に伴う色シェーディングの発生を抑制することができる。式（ａ）においてθ＝３°とすると、下式（ａ’）が得られる。
　Δ＝０．０５２（ｆ２／ｈ）　・・・（ａ’） In FIG. 3, the difference Δ is expressed by the following equation (a).
Δ = (f 2 / h) tan θ (a)
If the incident angle θ of the principal ray R on the imaging surface satisfies −3 ° ≦ θ ≦ + 3 ° at both the wide-angle end and the telephoto end, the wide-angle end and the telephoto end hardly change with little incidence angle θ. , And the occurrence of color shading accompanying the scaling can be suppressed. When θ = 3 ° in the formula (a), the following formula (a ′) is obtained.
Δ = 0.052 (f 2 / h) (a ′)
　また、前側焦点ＦＦ位置は、下式（ｂ）を満たす必要がある。
　Ｄ－Δ≦ｆｆ≦Ｄ＋Δ　・・・（ｂ）
　式（ｂ）に式（ａ’）を代入すると、下式（ｂ’）が得られる。
　Ｄ－０．０５２（ｆ２／ｈ）≦ｆｆ≦Ｄ＋０．０５２（ｆ２／ｈ）　・・・（ｂ’）
　さらに、式（ｂ’）は下式（ｂ”）のように変形することができる。
　|（ｆｆ－Ｄ）／ｆ２|≦０．０５２／ｈ　・・・（ｂ”） Further, the front focal point FF position needs to satisfy the following expression (b).
D−Δ ≦ ff ≦ D + Δ (b)
Substituting the formula (a ′) into the formula (b), the following formula (b ′) is obtained.
D−0.052 (f 2 /h)≦ff≦D+0.052(f 2 / h) (b ′)
Furthermore, the formula (b ′) can be transformed into the following formula (b ″).
| (Ff−D) / f 2 | ≦ 0.052 / h (b ″)
　このように、本実施形態に係る撮像光学系１およびこれを備える撮像装置によれば、条件式（１）および（２）を満足することで、ダイクロイックプリズム３への光の入射角をほとんど変化させることなく、広角端と望遠端との間で変倍することができる。これにより、広角端および望遠端の両方において色シェーディングが抑制された内視鏡画像９を取得することができるという利点がある。さらに、第３レンズ群Ｇ３にコンペンセータとしての機能をのみを付与し、変倍の際に固定である第４レンズ群Ｇ４を備えることによって、第３レンズ群Ｇ３の屈折力を弱くすることができ、第２レンズ群Ｇ２の移動に伴う主光線Ｒの入射角θの変化を第３レンズ群Ｇ３によって効果的に抑制することができるという利点がある。 As described above, according to the imaging optical system 1 and the imaging apparatus including the imaging optical system 1 according to the present embodiment, the incident angle of the light to the dichroic prism 3 is almost changed by satisfying the conditional expressions (1) and (2). It is possible to change the magnification between the wide-angle end and the telephoto end without causing the change. Thereby, there exists an advantage that the endoscopic image 9 by which color shading was suppressed in both a wide-angle end and a telephoto end can be acquired. Further, by providing the third lens group G3 only with a function as a compensator and including the fourth lens group G4 that is fixed at the time of zooming, the refractive power of the third lens group G3 can be weakened. There is an advantage that the change of the incident angle θ of the principal ray R accompanying the movement of the second lens group G2 can be effectively suppressed by the third lens group G3.
　なお、本実施形態においては、撮像光学系１が条件式（３）をさらに満足していることが好ましい。
（３）　　　　０．１８　＜　ｈ／ｆｗ　＜　０．２３
　モニタ４０の画面４１に表示される内視鏡画像９には、図４に示されるように、丸い開口部８ａを有し、内視鏡画像９の周囲を覆うマスク８が施される。特に細径の硬性内視鏡２０を使用する場合、内視鏡画像９を可能な限り大きく、かつ、内視鏡画像９の端部が欠けることなく、画面４１に表示したいというニーズがある。条件式（３）は、倍率が大きい広角端においても内視鏡画像９の全体が画面４１内に適切な大きさで表示されるように、広角端における倍率を規定したものである。 In the present embodiment, it is preferable that the imaging optical system 1 further satisfies the conditional expression (3).
(3) 0.18 <h / fw <0.23
The endoscopic image 9 displayed on the screen 41 of the monitor 40 is provided with a mask 8 having a round opening 8a and covering the periphery of the endoscopic image 9 as shown in FIG. In particular, when the small-diameter rigid endoscope 20 is used, there is a need to display the endoscope image 9 on the screen 41 without making the end portion of the endoscope image 9 as large as possible. Conditional expression (3) defines the magnification at the wide-angle end so that the entire endoscopic image 9 is displayed in an appropriate size on the screen 41 even at the wide-angle end where the magnification is large.
　特に関節鏡のような細径の硬性内視鏡と組み合わせる場合、図４に示されるように、開口部８ａの直径寸法を、画面４１の縦寸法の９０％程度にするためには、ｈ／ｆｗが０．１８となる。図５に示されるように、開口部８ａの直径寸法を、画面４１の縦寸法の６５％程度にするためには、ｈ／ｆｗが０．２３となる。したがって、条件式（３）を満足することで、画面４１上において内視鏡画像９を適切な大きさで表示することができ、画面４１の中心に対して内視鏡画像９が偏心したとしても、内視鏡画像９が欠けてしまうことを防止することができる。 In particular, when combined with a thin rigid endoscope such as an arthroscope, as shown in FIG. 4, in order to make the diameter of the opening 8a about 90% of the vertical dimension of the screen 41, h / fw is 0.18. As shown in FIG. 5, in order to make the diameter of the opening 8a about 65% of the vertical dimension of the screen 41, h / fw is 0.23. Therefore, when the conditional expression (3) is satisfied, the endoscopic image 9 can be displayed in an appropriate size on the screen 41, and the endoscopic image 9 is decentered with respect to the center of the screen 41. Also, it is possible to prevent the endoscopic image 9 from being lost.
　ｈ／ｆｗが０．１８以下である場合、図６に示されるように、画面４１上に表示されるマスク８の開口部８ａの直径寸法が画面４１の寸法よりも大きくなって内視鏡画像９の一部が欠けてしまい、内視鏡画像９の一部を画面４１上で観察できなくなる。ｈ／ｆｗが０．２３以上である場合、画面４１上に表示される内視鏡画像９が小さ過ぎて観察に適さない。 When h / fw is 0.18 or less, as shown in FIG. 6, the diameter dimension of the opening 8 a of the mask 8 displayed on the screen 41 is larger than the dimension of the screen 41, and the endoscopic image 9 is partly lost and part of the endoscopic image 9 cannot be observed on the screen 41. When h / fw is 0.23 or more, the endoscope image 9 displayed on the screen 41 is too small to be suitable for observation.
　本実施形態においては、撮像光学系１が条件式（４）をさらに満足していることが好ましい。
（４）　　　　０．３　＜　β４　＜　１
　ただし、β４は、第４レンズ群Ｇ４の近軸横倍率である。
　条件式（４）は、第４レンズ群Ｇ４の収斂作用の強さを規定したものである。条件式（４）を満足することで、第４レンズ群Ｇ４に適度な収斂作用を持たせることができ、第４レンズ群Ｇ４によって、撮像光学系１の射出瞳位置を適切に調整することができるとともに、収差を良好に補正することができる。 In the present embodiment, it is preferable that the imaging optical system 1 further satisfies the conditional expression (4).
(4) 0.3 <β4 <1
Where β4 is the paraxial lateral magnification of the fourth lens group G4.
Conditional expression (4) defines the strength of the converging action of the fourth lens group G4. When the conditional expression (4) is satisfied, the fourth lens group G4 can have an appropriate convergence function, and the fourth lens group G4 can appropriately adjust the exit pupil position of the imaging optical system 1. In addition, the aberration can be corrected satisfactorily.
　β４が０．３以下である場合、第４レンズ群Ｇ４の前側主点位置が物体側に寄り過ぎるか、または、第４レンズ群Ｇ４の屈折力が強過ぎることにより、撮像光学系１の射出瞳位置を適切な位置に調整することができなくなるとともに、収差を補正することが困難となる。β４が１以上である場合、第４レンズ群Ｇ４の前側主点位置が像面側に寄り過ぎるため、撮像光学系１の射出瞳位置を適切な位置に調整することができなくなるとともに、他のレンズ群Ｇ１，Ｇ２，Ｇ３の屈折力が相対的に強くなって収差を補正することが困難となる。 When β4 is 0.3 or less, the front principal point position of the fourth lens group G4 is too close to the object side, or the refractive power of the fourth lens group G4 is too strong, so that the emission of the imaging optical system 1 It becomes impossible to adjust the pupil position to an appropriate position, and it becomes difficult to correct the aberration. When β4 is 1 or more, the front principal point position of the fourth lens group G4 is too close to the image plane side, so that the exit pupil position of the imaging optical system 1 cannot be adjusted to an appropriate position, and other The refractive powers of the lens groups G1, G2, and G3 become relatively strong, making it difficult to correct aberrations.
　次に、上述した実施形態の実施例１から３について、図７から図１７を参照して以下に説明する。
　各実施例のレンズデータにおいて、ｒは曲率半径（ｍｍ）、ｄは面間隔（ｍｍ）、ｎはｄ線に対する屈折率、νはｄ線に対するアッべ数を示している。また、レンズデータにおいて、第１面（ｒ１）は、胴付面である。各種データに記載のｆ（全系の焦点距離）、ｆｆｗ、ｆｆｔ、Ｄおよびｈの単位は、ｍｍである。 Next, Examples 1 to 3 of the above-described embodiment will be described below with reference to FIGS.
In the lens data of each example, r is a radius of curvature (mm), d is a surface interval (mm), n is a refractive index with respect to the d line, and ν is an Abbe number with respect to the d line. In the lens data, the first surface (r1) is a body surface. The unit of f (focal length of the entire system), ffw, fft, D, and h described in various data is mm.
　図７，１０，１４のレンズ断面図において、「ｄ１３最小」は、広角端から望遠端に変倍する過程において第３レンズ群が最も像側に配置されるときの途中状態を示している。同図のｄ１３最小および望遠端において、図面が複雑になるのを防ぐために、ｄ５、ｄ８およびｄ１３以外の符号は省略している。 In the lens cross-sectional views of FIGS. 7, 10, and 14, “d13 minimum” indicates an intermediate state when the third lens unit is disposed closest to the image side in the process of zooming from the wide-angle end to the telephoto end. In order to prevent the drawing from becoming complicated at the minimum d13 and the telephoto end in the same figure, reference numerals other than d5, d8 and d13 are omitted.
　図８，９，１２，１３，１６，１７の球面収差、倍率色収差、歪曲収差およびコマ収差において、Ｃ線（６５６．２７ｎｍ）、ｄ線（５８７．５６ｎｍ）、ｅ線（５４６．０７ｎｍ）、Ｆ線（４８６．１３ｎｍ）およびｇ線（４３５．８３ｎｍ）における収差曲線を示している。同図の非点収差において、Ｍはメリジオナル像面を、Ｓはサジタル像面をそれぞれ示している。 In the spherical aberration, lateral chromatic aberration, distortion aberration and coma aberration in FIGS. 8, 9, 12, 13, 16, and 17, the C line (656.27 nm), d line (587.56 nm), e line (546.07 nm), The aberration curves for the F-line (486.13 nm) and the g-line (435.83 nm) are shown. In the astigmatism in the figure, M indicates a meridional image plane, and S indicates a sagittal image plane.
（実施例１）
　本発明の実施例１に係る撮像光学系のレンズ構成図を図７に示す。図８は広角端における各種収差図を示し、図９は望遠端における各種収差図を示している。本実施例のレンズデータおよび各種データは以下に示す通りである。
　本実施例においては、第３レンズ群の像側に第４レンズ群を設けて正の屈折力を第３レンズ群と第４レンズ群とに分配し、第３レンズ群の屈折力を低減している。これにより、第３レンズ群の移動に伴うダイクロイックプリズムおよび撮像面への入射角の変動を抑制し、色シェーディングの発生を抑制することができる。 (Example 1)
FIG. 7 shows a lens configuration diagram of the imaging optical system according to Example 1 of the present invention. FIG. 8 shows various aberration diagrams at the wide-angle end, and FIG. 9 shows various aberration diagrams at the telephoto end. The lens data and various data of this example are as shown below.
In this embodiment, a fourth lens group is provided on the image side of the third lens group to distribute the positive refractive power to the third lens group and the fourth lens group, thereby reducing the refractive power of the third lens group. ing. As a result, it is possible to suppress the variation in the incident angle to the dichroic prism and the imaging surface due to the movement of the third lens group, and to suppress the occurrence of color shading.
レンズデータ
面番号　　　　　　　　　ｒ　　　　　ｄ　　　　　　　ｎ　　　　　　ν
　　１　　　　　　　　　∞　　１．００　　１．７６８２　　７１．７０
　　２　　　　　　　　　∞　　４．１１
　　３　　　１３．９２６９　　１．７０　　１．５１７４　　５２．４３
　　４　　　－９．９３９２　　０．８０　　１．８４６７　　２３．７８
　　５　　　１７．７１２０　　　　ｄ５
　　６　　　－６．７０７３　　２．００　　２．００３３　　２８．２７
　　７　　　－３．７３２７　　０．９０　　１．７５５０　　５２．３２
　　８　　　１１．２５７２　　　　ｄ８
　　９　－１２２．９６６５　　２．６０　　１．７２００　　５０．２３
　１０　　－１４．４４７４　　０．３０
　１１　　　２６．５０１７　　２．４０　　１．７２００　　５０．２３
　１２　　－１３．０６４１　　１．５０　　１．８４６７　　２３．７８
　１３　　－５６．３０５２　　　ｄ１３
　１４　　　１３．６９２０　　２．３０　　１．７５５０　　５２．３２
　１５　－１４３．６４４９　　０．２０
　１６　　　８０．２６０４　　１．４０　　１．８４６７　　２３．７８
　１７　　　１４．２０７４　　４．０３ Lens data surface number rd n ν
1 ∞ 1.00 1.7682 71.70
2 ∞ 4.11
3 13.9269 1.70 1.5174 52.43
4 -9.9392 0.80 1.8467 23.78
5 17.7120 d5
6-6.7073 2.00 2.0033 28.27
7 -3.7327 0.90 1.7550 52.32
8 11.2572 d8
9 -122.9966 2.60 1.7200 50.23
10 -14.4474 0.30
11 26.5017 2.40 1.7200 50.23
12 -13.0641 1.50 1.8467 23.78
13 -56.3052 d13
14 13.6920 2.30 1.7550 52.32
15-143.6449 0.20
16 80.2604 1.40 1.8467 23.78
17 14.2074 4.03
各種データ
　　　　　　　広角端　　　　　　　ｄ１３最小　　　　　　　望遠端
ｄ５　　　　２．０８　　　　　　　　５．７８　　　　　　７．６６
ｄ８　　　　６．８９　　　　　　　　５．３１　　　　　　２．２５
ｄ１３　　　８．０４　　　　　　　　５．９２　　　　　　７．１０
ｆ　　１４．０１３２（ｆｗ）　１９．９３３２　　９．０９２０（ｆｔ）
ｆｆｗ＝８．５９３
ｆｆｔ＝－２．６７８
Ｄ＝７．００
ｈ＝３．００ Various data Wide angle end d13 minimum Telephoto end d5 2.08 5.78 7.66
d8 6.89 5.31 2.25
d13 8.04 5.92 7.10
f 14.0132 (fw) 19.3332 9.0920 (ft)
ffw = 8.593
fft = −2.678
D = 7.00
h = 3.00
　本実施例において、
　｜（ｆｆｗ－Ｄ）／ｆｗ２｜＝０．００８
　｜（ｆｆｔ－Ｄ）／ｆｔ２｜＝０．０１１
　０．０５２／ｈ＝０．０１７
　ｈ／ｆｗ＝０．２１４
　β４＝０．６２９
であり、条件式（１），（２），（３），（４）を満足している。 In this example,
| (Ffw−D) / fw 2 | = 0.008
| (Fft−D) / ft 2 | = 0.011
0.052 / h = 0.17
h / fw = 0.214
β4 = 0.629
It satisfies the conditional expressions (1), (2), (3), (4).
（実施例２）
　本発明の実施例２に係る撮像光学系のレンズ構成図を図１０に示す。図１１は、変倍時における各レンズ群Ｇ１、Ｇ２，Ｇ３，Ｇ４の主点位置の移動軌跡を示している。図１２は、広角端における各種収差図を示し、図１３は、望遠端における各種収差図を示している。本実施例のレンズデータおよび各種データは以下に示す通りである。 (Example 2)
FIG. 10 shows a lens configuration diagram of the imaging optical system according to Example 2 of the present invention. FIG. 11 shows the movement locus of the principal point position of each lens group G1, G2, G3, G4 at the time of zooming. FIG. 12 shows various aberration diagrams at the wide angle end, and FIG. 13 shows various aberration diagrams at the telephoto end. The lens data and various data of this example are as shown below.
　本実施例においては、第３レンズ群の像側に第４レンズ群を設けて正の屈折力を第３レンズ群と第４レンズ群とに分配し、第３レンズ群の屈折力を低減している。これにより、第３レンズ群の移動に伴うダイクロイックプリズムおよび撮像面への入射角の変動を抑制し、色シェーディングの発生を抑制することができる。さらに、本実施例において、第４レンズ群は、物体側から順に負レンズと正レンズとからなる。これにより、第４レンズ群の主点位置が第３レンズ群よりも像面側に位置し、望遠端において撮像面への光の入射角をさらに小さくすることができる。 In this embodiment, a fourth lens group is provided on the image side of the third lens group to distribute the positive refractive power to the third lens group and the fourth lens group, thereby reducing the refractive power of the third lens group. ing. As a result, it is possible to suppress variations in the incident angle to the dichroic prism and the imaging surface accompanying the movement of the third lens group, and it is possible to suppress the occurrence of color shading. Furthermore, in the present embodiment, the fourth lens group includes a negative lens and a positive lens in order from the object side. Thereby, the principal point position of the fourth lens group is located closer to the image plane side than the third lens group, and the incident angle of light on the imaging surface can be further reduced at the telephoto end.
レンズデータ
面番号　　　　　　　　　ｒ　　　　　ｄ　　　　　　　ｎ　　　　　　ν
　　１　　　　　　　　　∞　　１．００　　１．７６８２　　７１．７０
　　２　　　　　　　　　∞　　４．０１
　　３　　　１３．８０７１　　１．７０　　１．５１７４　　５２．４３
　　４　　　－８．７５０３　　０．８０　　１．８４６７　　２３．７８
　　５　　－１４．９４４７　　　　ｄ５
　　６　　　－６．３９９８　　２．４０　　２．００３３　　２８．２７
　　７　　　－３．５９５２　　０．９０　　１．７５５０　　５２．３２
　　８　　　１０．３２４８　　　　ｄ８
　　９　　　６７．５３３５　　２．９０　　１．７８８０　　４７．３７
　１０　　－１７．６９１７　　０．３０
　１１　　　２４．５５０５　　３．６０　　１．７２９２　　５４．６８
　１２　　－１１．４４３３　　１．５０　　１．８４６７　　２３．７８
　１３　　－５８．５８９０　　　ｄ１３
　１４　　－１２．５７５８　　１．４０　　１．７５５２　　２７．５１
　１５　　－５３．６６５９　　０．２０
　１６　　１１７．２４３０　　２．００　　１．７５５０　　５２．３２
　１７　　－１５．５１９９　　４．０３ Lens data surface number rd n ν
1 ∞ 1.00 1.7682 71.70
2 ∞ 4.01
3 13.8071 1.70 1.5174 52.43
4 -8.7503 0.80 1.8467 23.78
5-14.9447 d5
6-6.3998 2.40 2.0033 28.27
7 -3.5952 0.90 1.7550 52.32
8 10.3248 d8
9 67.5335 2.90 1.7880 47.37
10 -17.6917 0.30
11 24.5505 3.60 1.7292 54.68
12 -11.4433 1.50 1.8467 23.78
13-58.5890 d13
14 -12.75858 1.40 1.7552 27.51
15 -53.66659 0.20
16 117.2430 2.00 1.7550 52.32
17-155.5199 4.03
各種データ
　　　　　　　広角端　　　　　　　ｄ１３最小　　　　　　　　望遠端
ｄ５　　　　２．４２　　　　　　　　５．１２　　　　　　　６．８８
ｄ８　　　　６．５１　　　　　　　　５．９７　　　　　　　７．４４
ｄ１３　　　９．６９　　　　　　　　７．４４　　　　　　　９．３５
ｆ　１５．９１２０（ｆｗ）　１９．９１２０　　３１．６０６０（ｆｔ）
ｆｆｗ＝１０．５８５
ｆｆｔ＝３．８４１
Ｄ＝７．００
ｈ＝３．００ Various data Wide angle end d13 minimum Telephoto end d5 2.42 5.12 6.88
d8 6.51 5.97 7.44
d13 9.69 7.44 9.35
f 15.9120 (fw) 19.9120 31.6060 (ft)
ffw = 10.585
fft = 3.841
D = 7.00
h = 3.00
　本実施例において、
　｜（ｆｆｗ－Ｄ）／ｆｗ２｜＝０．０１４
　｜（ｆｆｔ－Ｄ）／ｆｔ２｜＝０．００３
　０．０５２／ｈ＝０．０１７
　ｈ／ｆｗ＝０．１８９
　β４＝０．９０８
であり、条件式（１），（２），（３），（４）を満足している。 In this example,
| (Ffw−D) / fw 2 | = 0.014
| (Fft−D) / ft 2 | = 0.003
0.052 / h = 0.17
h / fw = 0.189
β4 = 0.908
It satisfies the conditional expressions (1), (2), (3), (4).
（実施例３）
　本発明の実施例３に係る撮像光学系のレンズ構成図を図１４に示す。図１５は、変倍時における各レンズ群の主点位置の移動軌跡を示している。図１６は、広角端における各種収差図を示し、図１７は、望遠端における各種収差図を示している。本実施例のレンズデータおよび各種データは以下に示す通りである。 (Example 3)
FIG. 14 shows a lens configuration diagram of an imaging optical system according to Example 3 of the present invention. FIG. 15 shows the movement locus of the principal point position of each lens group at the time of zooming. FIG. 16 shows various aberration diagrams at the wide-angle end, and FIG. 17 shows various aberration diagrams at the telephoto end. The lens data and various data of this example are as shown below.
　本実施例においては、第３レンズ群の像側に第４レンズ群を設けて正の屈折力を第３レンズ群と第４レンズ群とに分配し、第３レンズ群の屈折力を低減している。これにより、第３レンズ群の移動に伴うダイクロイックプリズムおよび撮像面への入射角の変動を抑制し、色シェーディングの発生を抑制することができる。さらに、本実施例において、第４レンズ群は、物体側から順に正レンズと負レンズとからなる。これにより、第４レンズ群の主点位置が第３レンズ群よりも物体側に位置し、広角端において撮像面への光の入射角をさらに小さくすることができる。また、本実施例においては、第３レンズ群のレンズ面の内、最も物体側の面（面番号９）および最も像側の面（面番号）１３が平面であるので、レンズの加工コストを低減することができる。 In this embodiment, a fourth lens group is provided on the image side of the third lens group to distribute the positive refractive power to the third lens group and the fourth lens group, thereby reducing the refractive power of the third lens group. ing. As a result, it is possible to suppress variations in the incident angle to the dichroic prism and the imaging surface accompanying the movement of the third lens group, and it is possible to suppress the occurrence of color shading. Further, in the present embodiment, the fourth lens group includes a positive lens and a negative lens in order from the object side. Thereby, the principal point position of the fourth lens group is located closer to the object side than the third lens group, and the incident angle of light on the imaging surface can be further reduced at the wide angle end. In the present embodiment, among the lens surfaces of the third lens group, the most object-side surface (surface number 9) and the most image-side surface (surface number) 13 are flat surfaces. Can be reduced.
レンズデータ
面番号　　　　　　　　　ｒ　　　　　ｄ　　　　　　　ｎ　　　　　　ν
　　１　　　　　　　　　∞　　１．００　　１．７６８２　　７１．７０
　　２　　　　　　　　　∞　　４．２２
　　３　　　１４．９０７０　　１．７０　　１．５１７４　　５２．４３
　　４　　　－８．８３５０　　０．８０　　１．８４６７　　２３．７８
　　５　　－１５．２９８０　　　　ｄ５
　　６　　　－７．２９９０　　２．４０　　２．００３３　　２８．２７
　　７　　　－４．０２１０　　０．９０　　１．７５５０　　５２．３２
　　８　　　１１．６５３０　　　　ｄ８
　　９　　　　　　　　　∞　　２．９０　　１．７２９２　　５４．６８
　１０　　－１６．６８３０　　０．３０
　１１　　　１９．０２３０　　３．６０　　１．７２９２　　５４．６８
　１２　　－１９．０２３０　　１．５０　　１．８４６７　　２３．７８
　１３　　　　　　　　　∞　　　ｄ１３
　１４　　－１６．３９８０　　２．３０　　１．７２９２　　５４．６８
　１５　　　　　　　　　∞　　１．４０　　１．８４６７　　２３．７８
　１６　　　２１．０９５０　　４．０３ Lens data surface number rd n ν
1 ∞ 1.00 1.7682 71.70
2 ∞ 4.22
3 14.9070 1.70 1.5174 52.43
4 -8.8350 0.80 1.8467 23.78
5-15.2980 d5
6 -7.2990 2.40 2.0033 28.27
7 -4.0210 0.90 1.7550 52.32
8 11.6530 d8
9 ∞ 2.90 1.7292 54.68
10-16.6830 0.30
11 19.0230 3.60 1.7292 54.68
12-19.0230 1.50 1.8467 23.78
13 ∞ d13
14-16.3980 2.30 1.7292 54.68
15 ∞ 1.40 1.8467 23.78
16 21.0950 4.03
各種データ
　　　　　　　広角端　　　　　　　ｄ１３最小　　　　　　　　望遠端
ｄ５　　　　２．４９　　　　　　　　４．６２　　　　　　　６．８０
ｄ８　　　　７．６２　　　　　　　　６．８７　　　　　　　２．３２
ｄ１３　　　７．２１　　　　　　　　５．８５　　　　　　　８．２２
ｆ　　１５．９４１（ｆｗ）　　　１９．１２９　　３１．３０９（ｆｔ）
ｆｆｗ＝７．９４４
ｆｆｔ＝－９．９０４
Ｄ＝７．００
ｈ＝３．００ Various data Wide angle end d13 minimum Telephoto end d5 2.49 4.62 6.80
d8 7.62 6.87 2.32
d13 7.21 5.85 8.22
f 15.941 (fw) 19.129 31.309 (ft)
ffw = 7.944
fft = -9.904
D = 7.00
h = 3.00
　本実施例において、
　｜（ｆｆｗ－Ｄ）／ｆｗ２｜＝０．００４
　｜（ｆｆｔ－Ｄ）／ｆｔ２｜＝０．０１７
　０．０５２／ｈ＝０．０１７
　ｈ／ｆｗ＝０．１８８
　β４＝０．８０４
であり、条件式（１），（２），（３），（４）を満足している。 In this example,
| (Ffw−D) / fw 2 | = 0.004
| (Fft−D) / ft 2 | = 0.177
0.052 / h = 0.17
h / fw = 0.188
β4 = 0.804
It satisfies the conditional expressions (1), (2), (3), (4).
１　撮像光学系
２　カバーガラス
３　ダイクロイックプリズム
４，５，６　撮像素子
４ａ，５ａ，６ａ　撮像面
８　マスク
８ａ　開口部
９　内視鏡画像
１０　カメラヘッド
２０　硬性内視鏡
２３　接眼レンズ
３０　画像処理装置
４０　モニタ
４１　画面
Ｇ１　第１レンズ群
Ｇ２　第２レンズ群
Ｇ３　第３レンズ群
Ｇ４　第４レンズ群 DESCRIPTION OF SYMBOLS 1 Imaging optical system 2 Cover glass 3 Dichroic prism 4, 5, 6 Image pick-up element 4a, 5a, 6a Imaging surface 8 Mask 8a Opening part 9 Endoscopic image 10 Camera head 20 Hard endoscope 23 Eyepiece 30 Image processing apparatus 40 Monitor 41 Screen G1 First lens group G2 Second lens group G3 Third lens group G4 Fourth lens group

Claims (4)

  1. 　硬性内視鏡の接眼レンズを含むアイピース部の基端面に胴付面が突き当たるように前記硬性内視鏡の基端に接続されるカメラヘッドに内蔵され、前記接眼レンズから入射した光を結像する撮像光学系であって、
    　広角端と望遠端との間で変倍可能であり、１．５倍以上の変倍比を有するとともに、
    　物体側から像側へ向かって順に、正の屈折力を有する第１レンズ群と、負の屈折力を有する第２レンズ群と、正の屈折力を有する第３レンズ群と、正の屈折力を有する第４レンズ群とからなり、
    　下記の条件式（１）および（２）満足する撮像光学系。
    （１）　　　　｜（ｆｆｗ－Ｄ）／ｆｗ２｜　≦　０．０５２／ｈ
    （２）　　　　｜（ｆｆｔ－Ｄ）／ｆｔ２｜　≦　０．０５２／ｈ
    　ただし、
    　ｆｆｗは、前記胴付面を原点とした広角端での前記撮像光学系の前側焦点位置、
    　ｆｗは、広角端における前記撮像光学系の全系の焦点距離、
    　ｆｆｔは、前記胴付面を原点とした望遠端での前記撮像光学系の前側焦点位置、
    　ｆｔは、望遠端における前記撮像光学系の全系の焦点距離、
    　ｈは、前記撮像光学系の結像面における最大像高、
    　Ｄは、前記胴付面を原点とした前記硬性内視鏡の射出瞳位置
    であり、物体側から像側へ向かう光軸方向を正とする。     Built in the camera head connected to the proximal end of the rigid endoscope so that the body surface abuts the proximal end surface of the eyepiece part including the eyepiece of the rigid endoscope, and forms an image of light incident from the eyepiece An imaging optical system,
    The zoom ratio can be changed between the wide-angle end and the telephoto end, and has a zoom ratio of 1.5 times or more,
    In order from the object side to the image side, a first lens group having a positive refractive power, a second lens group having a negative refractive power, a third lens group having a positive refractive power, and a positive refractive power A fourth lens group having
    An imaging optical system that satisfies the following conditional expressions (1) and (2).
    (1) | (ffw−D) / fw 2 | ≦ 0.052 / h
    (2) | (fft−D) / ft 2 | ≦ 0.052 / h
    However,
    ffw is the front focal position of the imaging optical system at the wide-angle end with the body-mounted surface as the origin,
    fw is the focal length of the entire imaging optical system at the wide-angle end,
    fft is the front focal position of the imaging optical system at the telephoto end with the body-mounted surface as the origin,
    ft is the focal length of the entire imaging optical system at the telephoto end,
    h is the maximum image height on the imaging plane of the imaging optical system;
    D is the exit pupil position of the rigid endoscope with the torso surface as the origin, and the optical axis direction from the object side to the image side is positive.
  2. 　下記の条件式（３）を満足する請求項１の撮像光学系。
    （３）　　　　０．１８　＜　ｈ／ｆｗ　＜　０．２３     The imaging optical system according to claim 1, wherein the following conditional expression (3) is satisfied.
    (3) 0.18 <h / fw <0.23
  3. 　下記の条件式（４）を満足する請求項１または請求項２に記載の撮像光学系。
    （４）　　　　０．３　＜　β４　＜　１
    　ただし、
    　β４は、前記第４レンズ群の近軸横倍率
    である。     The imaging optical system according to claim 1 or 2, wherein the following conditional expression (4) is satisfied.
    (4) 0.3 <β4 <1
    However,
    β4 is the paraxial lateral magnification of the fourth lens group.
  4. 　前記第１レンズ群および前記第４レンズ群が、変倍時に固定であり、
    　前記広角端から前記望遠端への変倍時に、前記第２レンズ群が、物体側から像側へ一方向に移動し、前記第３レンズ群が、物体側から像側へ移動し、その後に物体側から像側へ移動する請求項１から請求項３のいずれかに記載の撮像光学系。     The first lens group and the fourth lens group are fixed at the time of zooming,
    At the time of zooming from the wide-angle end to the telephoto end, the second lens group moves in one direction from the object side to the image side, and the third lens group moves from the object side to the image side. The imaging optical system according to any one of claims 1 to 3, wherein the imaging optical system moves from the object side to the image side.
PCT/JP2015/084350 2015-03-18 2015-12-08 Image pickup optical system WO2016147501A1 (en)

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Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPH0545584A (en) * 1990-10-09 1993-02-23 Asahi Optical Co Ltd Power varying projection lens
JPH08179207A (en) * 1994-12-22 1996-07-12 Canon Inc Image pickup optical system
JPH11125770A (en) * 1997-10-21 1999-05-11 Olympus Optical Co Ltd Zoom image pickup optical system for endoscope
WO2010137238A1 (en) * 2009-05-26 2010-12-02 オリンパスメディカルシステムズ株式会社 Objective lens of endoscope

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPH0545584A (en) * 1990-10-09 1993-02-23 Asahi Optical Co Ltd Power varying projection lens
JPH08179207A (en) * 1994-12-22 1996-07-12 Canon Inc Image pickup optical system
JPH11125770A (en) * 1997-10-21 1999-05-11 Olympus Optical Co Ltd Zoom image pickup optical system for endoscope
WO2010137238A1 (en) * 2009-05-26 2010-12-02 オリンパスメディカルシステムズ株式会社 Objective lens of endoscope

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