Abstract:
A zooming optical system provided with a variable angle prism member of which the vertical angle is variable, and designed such that the vertical angle of the prism member is varied by a drive force applied from outside to thereby deflect a beam of light, wherein provision is made of a first lens unit having positive refractive power and a plurality of lens units including a movable lens unit rearwardly of the first lens unit, the first lens unit is divided into a front lens unit of negative refractive power and a rear lens unit of positive refractive power, and the prism member is disposed between the front lens unit and the rear lens unit.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to a zooming optical system (variable power optical system) containing a light deflecting member therein, and is particularly suitable for the so-called optical vibration preventing system of a video camera, a photographic camera, an observation mirror or the like which uses a variable angle prism as a light deflecting member and compensates for the movement of an image even when a vibration is applied to the optical system. 
     2. Related Background Art 
     When an attempt is made to take a photograph from a moving object such as a running vehicle or a flying aircraft, vibrations are transmitted to a phototaking system to thereby cause blurring to the photographed image. 
     There have heretofore been proposed various vibration preventing optical system having the function of preventing the blurring of a photographed image. 
     For example, in Japanese Patent Publication No. 56-21133, some optical members are moved in a direction to offset the vibrational displacement of an image caused by vibrations, in conformity with an output signal from detecting means for detecting the vibrated state of an optical apparatus, thereby achieving the stabilization of the image. 
     There has also been practiced a method of detecting the vibration of a photo-taking system by the utilization of an acceleration Kensor, and vibrating a lens group forming a part of the photo-taking system in a direction orthogonal to the optical axis thereof in conformity with a signal obtained at this time, thereby obtaining a static image. 
     Besides these, U.S. Pat. No. 2,959,088 proposes a vibration preventing optical system utilizing an inertial pendulum system wherein an afocal system comprising a first unit and a second unit of negative and positive refractive powers, respectively, which are equal in the absolute value of the focal length f is disposed forwardly of a photo-taking system and when the photo-taking system vibrates, the second unit is used as a movable lens unit for vibration prevention and is gimbal-supported at the focus position thereof. 
     In Japanese Laid-Open Patent Application No. 61-223819, there is described an example in which, in a photo-taking system wherein a variable angle prism is disposed most adjacent to the object side, the vertical angle of the variable angle prism is varied correspondingly to the vibration of the photo-taking system to thereby deflect an image and achieve the stabilization of the image. 
     However, disposing the variable angle prism most adjacent to the object side has given rise to a problem that an attempt to provide a wide angle to the optical system which is the main body results in the bulkiness of the prism. In contrast, there have been proposed several systems whereby a variable angle prism is disposed in a zoom lens, but as compared with a case where the prism is disposed adjacent to the object side, the correction angle necessary during vibration prevention is liable to become great, or the size of the optical system on the object side is liable to become larger than the prism for the purpose of securing a quantity of light during vibration prevention. 
     Also, when a variable angle prism is disposed in a variable power portion or more adjacent to the image plane side than to the variable power portion, the relation between the angle of inclination of the photo-taking system and the amount of variation in the vertical angle of the prism necessary to correct it is changed by focal-length change and therefore, the information of the focal length becomes necessary during correction. 
     SUMMARY OF THE INVENTION 
     The present invention has as its first object the provision of a zooming optical system in which the optical system is not made so large as compared with a case where a variable angle prism is not contained in the optical system. 
     The present invention has as its second object the provision of a zooming optical system which need not use the information of the focal length. 
     According to a preferred embodiment of the present invention, in an optical system which is provided with a variable angle prism member of which the vertical angle is variable and which is designed such that the vertical angle of said prism member is varied by a drive force imparted from outside to thereby deflect a beam of light, there are provided a first lens unit having positive refractive power and a plurality of lens units including a movable lens unit disposed rearwardly of the first lens unit, said first lens unit being divided into a front lens unit and a rear lens unit, said prism member being disposed between said front lens unit and said rear lens unit. In this case, it is desirable that the refractive power of the front lens unit be negative and the refractive power of the rear lens unit be positive. An example of the variable angle prism is known and therefore, detailed description thereof is omitted, but there is one in which two transparent rigid members are connected together by bellows to provide a water-tight space and this space is filled with liquid such as silicone oil, or one in which the space is filled with silicon rubber instead of liquid. 
     As an example of said plurality of lens units, there are a second lens unit of negative refractive power, a third lens unit of positive refractive power and a fourth lens unit of positive refractive power, or a second lens unit of negative refractive power, a third lens unit of negative refractive power, a fourth lens unit of positive refractive power and a fifth lens unit of positive refractive power. 
     By a variable angle prism being disposed in the first lens unit of the above-described zooming optical system, the downsizing of the system becomes possible and a wider angle can also be realized by a predetermined construction, and the system is made compact, and this is useful to improve the usability of the apparatus. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a cross-sectional view of a lens according to Embodiment 1. 
     FIG. 2 is a cross-sectional view of a lens according to Embodiment 2. 
     FIG. 3 is a cross-sectional view of a lens according to Embodiment 3. 
     FIGS. 4A to 4D show aberrations at the wide angle end of Numerical Value Embodiment 1. 
     FIGS. 5A to 5D show aberrations at the medium angle of field of Numerical Value Embodiment 1. 
     FIGS. 6A to 6D show aberrations at the telephoto end of Numerical Value Embodiment 1. 
     FIGS. 7A to 7D show aberrations at the wide angle end of Numerical Value Embodiment 2. 
     FIGS. 8A to 8D show aberrations at the medium angle of field of Numerical Value Embodiment 2. 
     FIGS. 9A to 9D show aberrations at the telephoto end of Numerical Value Embodiment 2. 
     FIGS. 10A to 10D show aberrations at the wide angle end of Numerical Value Embodiment 3. 
     FIGS. 11A to 11D show aberrations at the medium angle of field of Numerical Value Embodiment 3. 
     FIGS. 12A to 12D show aberrations at the telephoto end of Numerical Value Embodiment 3. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1 shows the cross-section of a lens according to Embodiment 1 of the present invention. 
     In FIG. 1, the reference numeral 1 designates a first lens unit having positive refractive power and adapted to be fixed during focal-length change and focusing, the reference numeral 2 denotes a second lens unit having negative refractive power and having the focal-length changing function, the reference numeral 3 designates a third lens unit having positive refractive power and adapted to be fixed during focal-length change and focusing, and the reference numeral 4 denotes a fourth lens unit having positive refractive power, effecting the correction of the movement of an image plane resulting from focal-length change and having the focusing function. Zooming is done by simultaneous movement of the second lens unit and the fourth lens unit. 
     The reference characters 1a and 1b designate a front lens unit of negative refractive power and a rear lens unit of positive refractive power, respectively, and a variable angle prism VAP is disposed in a space of fixed interval. In the present embodiment, the front lens unit 1a is particularly comprised of a negative single meniscus lens for the purpose of downsizing, but alternatively may be comprised of two negative single lenses or may be comprised of negative and positive lenses for the correction of chromatic aberration. In an actual photographing system, besides one to four optical systems, there are provided vibration detecting means 12 such as an acceleration sensor for finding the amount of vibration and prism driving means 11 for driving the variable angle prism, and the vertical angle of the variable angle prism is varied in conformity with the amount of vibration to thereby achieve stabilization of photographed images. 
     On the other hand, when the focal length of the first lens unit is f1 and the focal length of the whole system is f and the magnification of the second and subsequent lens groups is β, 
     
         f=f1·β                                       (1) 
    
     and therefore, if f1 is shortened with the magnification of the second and subsequent lens units kept constant, the focal length of the whole system will become shorter, that is, a wider angle can be achieved. 
     However, shortening the focal length of the first lens unit with the objectpoint of the second lens unit, i.e., the image point of the first lens unit, kept at a predetermined location would make the principal point interval between the first lens unit and the second lens unit smaller, andthus, at the wide angle end, the first lens unit and the second lens unit would mechanically interfere with each other. 
     In the present embodiment, the first lens unit 1 is comprised of the front lens unit 1a having negative refractive power and the rear lens unit 1b having positive refractive power, and the spacing therebetween is appropriately kept, whereby the rear principal point is moved rearwardly (toward the image point) to thereby shorten the focal length of the first lens unit and also secure a space between the first lens unit and the second lens unit. By the variable angle prism being disposed between the front lens unit 1a and the rear lens unit 1b, the whole system is made more compact than when the variable angle prism is simply disposed most adjacent to the object side, while a wider angle of the lens system is realized. The front lens unit 1a also has the function as a protective glass for preventing any force from being applied directly from outside tothe variable angle prism. 
     Usually, when such a protective glass is constructed of a planar plate, rays of light will and return between the image pickup surface and the surface of the protective glass to cause a ghost. 
     In the present embodiment, this protective glass corresponds to a case where it has a suitable curvature, and therefore the intensity of such ghost can be made small. 
     Further, to achieve a wider angle with a splendid optical performance maintained, it is desirable that the following condition be satisfied: 
     
         3.0&lt;|f1a/f1|&lt;7.0                         (2) 
    
     where f1a and f1 are the focal lengths of the front lens unit 1a and the first lens unit, respectively. It is more preferable to set the upper limit value of this conditional expression to 6.0, or it will be more effective if the lower limit value of this conditional expression is set to 3.5. If the focal length of the front lens unit becomes short beyond the lower limit of conditional expression (2), it will be advantageous fora wider angle, but the correction of spherical aberration and coma at the telephoto end will become difficult and eccentric coma occurring during vibration prevention will become great, and this is not good. 
     If conversely, the focal length of the front lens unit becomes long beyond the upper limit of the conditional expression (2), a wider angle could notbe sufficiently achieved. 
     In the present embodiment, the first lens unit is fixed during focal-lengthchange or during focusing, but may be moved during focal-length change or focusing to such a degree as not to affect the control of the variable angle prism. 
     The cross-sectional shape of the lens of FIG. 2 corresponds to numerical value Embodiment 2, and each lens shape differs from the lens system of FIG. 1, but the basic arrangement is the same as that of FIG. 1. 
     FIG. 3 is a cross-sectional view of a lens corresponding to Numerical ValueEmbodiment 3. The reference numeral 1 designates a first lens unit of positive refractive power, the reference numeral 2 denotes a second lens unit of negative refractive power, the reference numeral 3 designates a third lens unit of negative refractive power, the reference numeral 4 denotes a fourth lens unit of positive refractive power, and the referencenumeral 5 designates a fifth lens unit of positive refractive power. 
     The second lens unit has the focal-length changing function, the third lensunit has the function of such a compensator that image plane fluctuation during focal-length change becomes null for a particular object distance, and the fifth lens unit has the focusing function. 
     By the third lens unit being made to have the function as a compensator fora particular object distance, the influence of the focus movement during zooming is reduced. 
     In the present embodiment, the fifth lens unit becomes fixed during focal-length change for an object distance 385 (when the focal length at the wide angle end is 1), and when the object distance is greater than this, the fifth lens unit is moved toward the image plane side during the focal-length change from the wide angle and to the telephoto end, and whenthe object distance is shorter than this, the fifth lens unit is moved toward the object side. 
     Some numerical value embodiments of the present invention are shown below. 
     In the numerical value embodiments, Ri represents the radius of curvature of the ith lens surface from the object side, Di represents the lens thickness or air space of the ith lens from the object side, ni and νi represent the refractive index and Abbe number, respectively, of the glassof the ith lens from the object side. 
     The plane parallel glass disposed most adjacent to the image plane side is an equivalent member such as a face plate or a filter. 
     The relations between conditional expression (1) and the various numerical values in the numerical value embodiments are shown in Table 1 below. 
     Also, when the direction of the optical axis from the object side toward the image plane is the X-axis and the direction perpendicular to the optical axis is the H-axis, and R is the paraxial radius of curvature, andK is the come constant, and B, C, D and E are aspherical surface coefficients, the aspherical surface is expressed by the following equation: ##EQU1## 
     
         ______________________________________Numerical Value Embodiment 1______________________________________f = 1 to 12.66      fno = 1:1.85 to 3.59                       2ω = 59° to 5.1°r1 = 7.2491      d1 = 0.3011 n1 = 1.60311                              ν1 = 60.7r2 = 4.8359      d2 = variabler3 = ∞      d3 = 0.2125 n2 = 1.52300                              ν2 = 58.6r4 = ∞      d4 = 0.5845 n3 = 1.41650                              ν3 = 52.2r5 = ∞      d5 = 0.2125 n4 = 1.52300                              ν4 = 58.6r6 = ∞      d6 = 0.1417r7 = 7.9937      d7 = 0.2125 n5 = 1.84666                              ν5 = 23.8r8 = 3.9434      d8 = 0.7261 n6 = 1.60311                              ν6 = 60.7r9 = -189.8373      d9 = 0.0354r10 = 4.2844      d10 = 0.5756                  n7 = 1.77250                              ν7 = 49.6r11 = 51.2942      d11 = variabler12 = 4.0459      d12 = 0.1063                  n8 = 1.88300                              ν8 = 40.8r13 = 1.1525      d13 = 0.4343r14 = -1.5931      d14 = 0.1063                  n9 = 1.69680                              ν9 = 55.5r15 = 2.7898      d15 = 0.1594r16 = 3.2370      d16 = 0.2834                  n10 = 1.84666                              ν10 = 23.8r17 = -8.9972      d17 = variabler18 = (stop)      d18 = 0.21r19 = aspherical      d19 = 0.6730                  n11 = 1.58313                              ν11 = 59.4r20 = -2.7974      d20 = 0.0705r21 = -2.2248      d21 = 0.1594                  n12 = 1.77250                              ν12 = 49.6r22 = -3.5587      d22 = variabler23 = 7.6081      d23 = 0.1240                  n13 = 1.84666                              ν13 = 23.8r24 = 2.2485      d24 = 0.5490                  n14 = 1.51742                              ν14 = 52.4r25 = -7.2195      d25 = 0.0354r26 = 4.3184      d26 = 0.4073                  n15 = 1.51633                              ν15 = 4.2r27 = -5.8237      d27 = 0.8855r28 = ∞      d28 = 0.8855                  n16 = 1.51633                              ν16 = 64.2r29 = ∞______________________________________focal length      1.00        4.22        12.66variable spacingd2         1.13        1.13        1.13d11        0.19        2.69        3.76d17        3.85        1.35        0.28d22        2.30        1.39        2.92______________________________________Aspherical surface19th surface r = 4.87464 K = -1.06095 B = 6.72813D 04 C = -1.70127D 03 D = 2.73867D 03 E = -7.07303D 04 &#34;DOil&#34; represents &#34;X10.sup.-i &#34;. 
    
     
         ______________________________________Numerical Value Embodiment 2______________________________________f = 1 to 12.05      fno = 1:1.65 to 3.31                       2ω = 60.8° to 5.6°r1 = 24.8798      d1 = 0.3178 n1 = 1.60311                              ν1 = 60.7r2 = 8.8590      d2 = 0.9780r3 = ∞      d3 = 0.2934 n2 = 1.52300                              ν2 = 58.6r4 = ∞      d4 = 0.8068 n3 = 1.41650                              ν3 = 52.2r5 = ∞      d5 = 0.2934 n4 = 1.52300                              ν4 = 58.6r6 = ∞      d6 = 0.1956r7 = 8.7614      d7 = 0.22   n5 = 1.84666                              ν5 = 23.8r8 = 4.6304      d8 = 1.0147 n6 = 1.60311                              ν6 = 60.7r9 = -19.2998      d9 = 0.0489r10 = 4.4664      d10 = 0.5868                  n7 = 1.71300                              ν7 = 53.8r11 = 15.6609      d11 = variabler12 = 14.9152      d12 = 0.1467                  n8 = 1.77250                              ν8 = 49.6r13 = 1.1820      d13 = 0.4841r14 = -3.0606      d14 = 0.1467                  n9 = 1.69680                              ν9 = 55.5r15 = 3.0606      d15 = 0.1834r16 = 2.6739      d16 = 0.3178                  n10 = 1.84666                              ν10 = 23.8r17 = 18.3932      d17 = variabler18 = (stop)      d18 = 0.2689r19 = aspherical      d19 = 0.6112                  n11 = 1.58313                              ν11 = 59.4r20 = -11.4207      d20 = variabler21 = 3.2544      d21 = 0.1467                  n12 = 1.84666                              ν12 = 23.8r22 = 1.5923      d22 = 0.0274r23 = 1.7369      d23 = 0.9046                  n13 = 1.58313                              ν13 = 59.4r24 = aspherical      d24 = 0.7335r25 = ∞      d25 = 1.0611                  n14 = 1.51633                              ν14 = 64.2r26 = ∞______________________________________focal length      1.00        3.56        12.05variable spacingd11        0.22        2.80        4.32d17        4.40        1.82        0.31d20        1.99        0.91        1.98______________________________________Aspherical surface19th surface K = 3.27803 b = 3.96486D 01 c = -1.05281D 02 D = 4.73325D 04 = -3.78976D 0424th surface K = -4.31741 B = 1.07211D + 01 C = 1.34349D 02 D = 2.31038D 0E = 2.03980D 03 
    
     
         ______________________________________Numerical Value Embodiment 3______________________________________f = 1 to 11.51      fno = 1:1.65 to 2.77                       2ω = 58.5° to 5.6°r1 = 38.7375      d1 = 0.2626 n1 = 1.60311                              ν1 = 60.7r2 = 12.2336      d2 = 0.7002r3 = ∞      d3 = 0.2101 n2 = 1.52300                              ν2 = 58.6r4 = ∞      d4 = 0.5777 n3 = 1.41650                              ν3 = 52.2r5 = ∞      d5 = 0.2101 n4 = 1.52300                              ν4 = 58.6r6 = ∞      d6 = 0.1751r7 = 7.7081      d7 = 0.2451 n5 = 1.84666                              ν5 = 23.8r8 = 3.9667      d8 = 1.1028 n6 = 1.60311                              ν6 = 60.7r9 = -19.8893      d9 = 0.0350r10 = 3.7864      d10 = 0.6127                  n7 = 1.77250                              ν7 = 49.6r11 = 10.5603      d11 = variabler12 = 8.0018      d12 = 0.1225                  n8 = 1.77250                              ν8 = 49.6r13 = 1.1709      d13 = 0.5094r14 = -5.3150      d14 = 0.1050                  n9 = 1.71300                              ν9 = 53.8r15 = 1.9159      d15 = 0.1663r16 = 2.0181      d16 = 0.3501                  n10 = 1.84666                              ν10 = 23.8r17 = 13.0216      d17 = variabler18 = -2.4853      d18 = 0.1400                  n11 = 1.71300                              ν11 = 53.8r19 = -32.2760      d19 = variabler20 = (stop      d20 = 0.3501r21 = 10.0139      d21 = 0.5252                  n12 = 1.51823                              ν12 = 59.0r22 = -3.4547      d22 = 0.0263r23 = 4.9535      d23 = 0.4726                  n13 = 1.60311                              ν13 = 60.7r24 = -11.3311      d24 = 0.0263r25 = 3.8040      d25 = 0.3676                  n14 = 1.51633                              ν14 = 64.2r26 = 24.4906      d26 = 0.1838r27 = -5.1796      d27 = 0.1400                  n15 = 1.80518                              ν15 = 25.4r28 = 10.8253      d28 = variabler29 = 3.5539      d29 = 0.4201                  n16 = 1.51633                              ν16 = 64.2r30 = -10.1088      d30 = 0.0263r31 = 1.8311      d31 = 0.1751                  n17 = 1.84666                              ν17 = 23.8r32 = 1.4193      d32 = 0.1663r33 = 2.5917      d33 = 0.3676                  n18 = 1.48749                              ν18 = 70.2r34 = 6.8372      d34 = 0.8753r35 = ∞      d35 = 0.8753                  n19 = 1.51633                              ν19 = 64.2r36 = ∞______________________________________focal length      1.00        4.05        11.51variable spacingd11        0.16        2.54        3.33d17        3.00        0.48        0.70d19        1.17        1.31        0.29d28        1.14        1.14        1.14______________________________________A distance to an object is 385 (constant). 
    
     
                       TABLE 1______________________________________Numerical valueEmbodiment  1            2      3______________________________________|fla/fl|       4.692        5.645  3.780______________________________________