JP3078165B2 - Aspherical zoom lens and video camera - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an aspherical zoom lens which is used in a three-panel video camera or the like and has a high zoom ratio and a long back focus, and a video camera using the aspherical zoom lens. Things.

[0002]

2. Description of the Related Art Recent video cameras are required to have high image quality as well as operability and mobility, and in response to this, imaging devices having a small size and a high resolution are becoming mainstream.
Accordingly, there is a strong demand for a high-performance zoom lens having a large aperture ratio, small size, light weight, and high performance. Further, it is desirable that the zoom lens be reduced in cost by reducing the number of components while maintaining high performance.

[0003] However, a high-magnification zoom lens generally requires not only an increase in lens diameter and lens length but also a large number of lenses to achieve more severe aberration correction. For this reason, high-magnification zoom lenses are generally large and heavy and tend to be expensive, and many are not suitable for consumer video cameras.

Next, an example of the above-mentioned conventional zoom lens for a video camera will be described with reference to the drawings (for example, disclosed in Japanese Patent Application No. 5-135016). FIG.
FIG. 1 is a configuration diagram of a conventional zoom lens for a video camera. In FIG. 21, a first lens group 21 is a lens group of a condenser section, a second lens group 22 is a lens group of a variable power section, a third lens group 23 is a lens group of a condenser section, and a fourth lens group 24 is a focus. FIG. Behind the fourth lens group 24, a color separation optical system 25, a face plate 26 including a quartz filter and an image sensor, and an image plane 27 are provided. Of the above lens groups, the third lens group 23
The central convex lens of the fourth lens group 24 is constituted by an aspherical lens, and the other lenses are constituted by spherical lenses.

The operation of the thus-configured zoom lens for a video camera will be described. The first lens group 21 fixed to the image forming plane 27 has an image forming action,
The lens group 22 moves on the optical axis to change the magnification, and changes the focal length of the entire system. Third lens group 23 which is a fixed group
Collects the divergent light generated by the second lens group 22. The fourth lens group 24 moves on the optical axis and performs a focusing action. Further, the fourth lens group 24 eliminates the fluctuation of the image plane position caused by the movement of the second lens group 22 during zooming by moving the fourth lens group 24 itself. For this reason, the imaging surface 27 is always kept at a fixed position.

[0006]

However, as described above, in a zoom lens mainly constituted by a spherical lens,
If an attempt is made to secure a long back focus with a zoom ratio of about 10 times, it becomes difficult to correct aberrations in the entire zoom area and in the entire imaging distance, leaving a problem that a high-quality image cannot be realized.

SUMMARY OF THE INVENTION The present invention has been made in view of such a conventional problem, and employs an optimal aspherical shape for the first lens unit or an optimal aspherical shape for the second lens unit. , A high-performance aspherical zoom lens with a simple configuration, a zoom ratio of about 10 times, and a long back focus that can insert a color separation optical system is realized. It is an object to provide a video camera using a spherical zoom lens.

[0008]

According to a first aspect of the present invention, there is provided a first lens unit having a positive refractive power and fixed with respect to an image plane, and an optical axis having a negative refractive power. The second lens group having a zooming action by moving upward, the third lens group having a positive refractive power fixed to the image plane and having a condensing action, the movement of the second lens group, and the movement of an object An aspherical zoom lens including a fourth lens group having a positive refractive power that moves on the optical axis so as to keep a fluctuating image plane at a fixed position from the reference plane, wherein the third lens group and the fourth lens group Has an air gap, the first lens group includes a concave lens, a convex lens, and a meniscus convex lens in order from the object side, and the second lens group includes a meniscus concave lens , a biconcave lens, and a convex lens. The three lens groups have at least one aspheric surface. It is configured to include a lens, a fourth
The lens group includes a lens having at least one or more aspheric surfaces, a cemented lens having two lenses, and one convex lens , where fW is the focal length at the wide-angle end, fi
(I = 1, 2, 3, 4) is the focal length of the ith lens group, B
F is the distance between the last lens surface and the imaging surface in air
The distance, d12, is between the air between the third lens group and the fourth lens group.
The distance r11 is the object side of the convex lens constituting the third lens group.
The radius of curvature of the surface, r13, is determined by the cementing lens constituting the fourth lens group.
The radius of curvature of the surface of the lens closest to the object, r17, is the fourth lens.
Is the radius of curvature of the image side of the convex lens that constitutes the lens group
Come, (1) 5.5 <f1 / fW <6.3 (2) 1.0 <| f2 | / fW <1.2 (3) 5.3 <f3 / fW <6.2 (4) 3 0.0 <f4 / fW <3.3 (5) 3.2 <BF / fW <4.2 (6) 0.1 <d12 / f4 <0.4 (7) 0.5 <r11 / f3 <0 there / f4 <0.8 those wherein the respectively satisfy | .9 (8) 1.1 <| r13 | / f4 <2.4 (9) 0.6 <| r17.

According to a second aspect of the present invention, a first lens unit having a positive refractive power and fixed to an image plane and moving on an optical axis having a negative refractive power are arranged in order from the object side. The second lens group having a zooming action, the third lens group having a positive refractive power fixed to the image plane and having a condensing action, and the image plane fluctuated by the movement of the second lens group and the movement of the object An aspherical zoom lens including a fourth lens group having a positive refractive power that moves on the optical axis so as to be kept at a fixed position from the surface, wherein the third lens group and the fourth lens group have an air gap. And
The first lens group includes, in order from an object side than <br/> a concave lens and a convex lens in order meniscus convex lens, and is configured to include a lens having at least one surface or aspherical, the second lens group, a meniscus concave lens and a biconcave lens And a convex lens, the third lens group includes a single lens having at least one aspheric surface, the fourth lens group includes a lens having at least one aspheric surface, and 2
Cemented lens and is configured to include one convex lens of the single structure
Where fW is the focal length at the wide-angle end, fi (i = 1,
2, 3, 4) are the focal length of the i-th lens group, and BF is in the air.
At the distance from the lens final surface to the image forming surface, d12
The air gap between the third lens group and the fourth lens group, r11,
Half the curvature of the object side surface of the convex lens constituting the third lens group
The diameter r13 is the most of the cemented lens constituting the fourth lens group.
The radius of curvature of the surface from the object, r17, constitutes the fourth lens group
When the radius of curvature of the image side surface of the convex lens that, (1) 3.0 <f1 / fW <8.0 (2) 0.5 <| f2 | / fW <1.6 (3) 5.3 <f3 /FW<7.0 (4) 2.0 <f4 / fW <5.0 (5) 1.5 <BF / fW <5.0 (6) 0.02 <d12 / f4 <1.0 (7) ) 0.3 <r11 / f3 <1.5 (8) 0.3 <| r13 | / f4 <3.0 (9) 0.3 <| a / f4 <1.5 that respectively satisfy | r17 It is a feature.

[0010] The invention according to claim 3 of the present application is arranged in order from the object side.
A first lens having a positive refractive power and fixed with respect to the image plane.
Group has negative refractive power and changes by moving on the optical axis.
Second lens unit having a doubling effect, fixed to the image plane
Third lens group having positive refractive power and second lens having optical action
Based on image plane that fluctuates due to movement of group and object
Positive bending moving on the optical axis to keep it at a fixed position from the surface
An aspherical zoom lens including a fourth lens group having a folding power.
The third lens group and the fourth lens group have an air gap,
The first lens group includes a concave lens and a convex lens in order from the object side.
A second lens group including a meniscus convex lens
Is a meniscus concave lens, a biconcave lens and a convex lens, and
Including a lens having at least one aspheric surface
And at least one surface of the third lens group is aspheric.
The fourth lens group includes a small number of lenses.
At least one or more aspherical lenses, and two lenses
It is comprised including the cemented lens of the structure and one convex lens,
fW is the focal length at the wide angle end, and fi (i = 1, 2, 2)
3, 4) are the focal length of the i-th lens group, and BF is in the air.
The distance from the last lens surface to the image forming surface, d12, is the third
The air gap between the lens group and the fourth lens group, r11, is third.
The radius of curvature of the object side surface of the convex lens constituting the lens group, r
13 is the most object of the cemented lens constituting the fourth lens group
The radius of curvature of the surface, r17, is the convexity of the fourth lens group.
Assuming that the radius of curvature of the image side surface of the lens is: (1) 3.0 <f1 / fW <8.0 (2) 0.5 <| f2 | / fW <1.6 (3) 5.3 <f3 / fW <7.0 (4) 2.0 <f4 / fW <5.0 (5) 1.5 <BF / fW <5.0 (6) 0.02 <d12 / f4 <1.0 (7) 0.3 <r11 / f3 <1.5 (8) 0.3 <| r13 | / f4 <3.0 (9) It is characterized by satisfying 0.3 <| r17 | / f4 <1.5 , respectively. It is assumed that.

[0011] The invention according to claim 6 of the present application is arranged in the order from the object side.
A first lens having a positive refractive power and fixed with respect to the image plane.
Group has negative refractive power and changes by moving on the optical axis.
Second lens unit having a doubling effect, fixed to the image plane
A third lens unit having a positive refractive power having an optical effect,
Image plane that fluctuates due to the movement of lens groups and the movement of objects
Move positive on the optical axis to keep it at a fixed position from the reference plane.
Aspherical zoom lens including a fourth lens group with a refractive power of
The distance between the third lens group and the fourth lens group is an air gap.
The first lens group includes a concave lens and a convex lens in order from the object side.
Lens and meniscus convex lens, and at least one surface
The second lens includes a lens having an aspherical shape.
Lens group consists of meniscus concave lens, biconcave lens and convex lens
And the third lens group has at least one surface
The fourth lens group is configured to include an aspheric single lens.
Is a lens having at least one or more aspherical shapes,
And a two-lens cemented lens and one convex lens.
FW is the focal length at the wide-angle end, fi (i =
1, 2, 3, 4) are the focal length of the i-th lens group, BF
Is the distance from the last lens surface to the imaging surface in the air,
d12 is the distance between the third lens group and the fourth lens group.
The air gap, r11, is a convex lens constituting the third lens group.
The radius of curvature r13 of the object side surface is the same as that of the fourth lens group.
Radius of curvature of the surface of the cemented lens that forms the most from the object, r1
7 is the curvature of the image side surface of the convex lens constituting the fourth lens group.
Assuming that the rate radius is (1) 5.5 <f1 / fW <6.3 (2) 1.0 <| f2 | / fW <1.2 (3) 5.3 <f3 / fW <6.2 (4) 3.0 <f4 / fW <3.3 (5) 3.2 <BF / fW <4.2 (6) 0.1 <d12 / f4 <0.4 (7) 0.5 <r11 /f3<0.9 (8) 1.1 <| r13 | / f4 <2.4 (9) 0.6 <| r17 | / is characterized in that the f4 a <0.8 respectively satisfying .

[0012]

According to the present invention having the above features,
According to the invention described above, the first lens group includes a concave lens and a convex lens.
And a meniscus convex lens with positive refracting power
Use The second lens group includes a meniscus concave lens and a biconcave lens.
It has a lens and a convex lens, has a negative refractive power, and is on the optical axis.
The zooming action is effected by moving. The third lens group
It consists of an aspherical single lens of positive refractive power with a convex surface facing the object side.
And acts to condense light at a fixed position. The fourth lens group is an object
A cemented lens consisting of two lenses in order from the body side, with the convex side facing the image side
Convex lens and at least one aspheric surface
Has a positive refractive power and moves on the optical axis.
By doing so, the function of adjusting the focus can be obtained. or
According to the seventh aspect of the present invention, by using the aspherical zoom lens for the video camera, an image plane with good aberration can be formed on the imaging element.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Aspherical zoom lenses according to first to sixth embodiments of the present invention will be described in detail with reference to the drawings and tables. FIG. 1 is a configuration diagram of an aspherical zoom lens according to first to fifth embodiments of the present invention. In FIG. 1, the aspherical zoom lens includes a first lens group 1, a second lens group 2, a third lens group 3, and a fourth lens group arranged from an object position to an image position. And on the optical axis of each lens group,
A color separation optical system 5 and a face plate 6 are provided behind the lens group 4, and an image plane is formed on an image plane 7. The color separation optical system 5 is an optical system that separates outgoing light from the fourth lens group 4 into R, B, and G components. The face plate 6 is quartz
Equivalent to filters and image sensors and their faceplates
It is a flat plate.

Next, each lens group will be described. The first lens group 1 is composed of three lenses 1a, 1b, and 1c, and is a fixed group of lenses having a positive refractive power and performing an image forming operation. The lens 1a has a thickness d1, a radius of curvature r of the object-side surface.
1, an aspheric lens having a radius of curvature r2 of the image-side surface. The lens 1b is a spherical lens having a thickness d2, a radius of curvature r2 on the object side, and a radius of curvature r3 on the image side. The lens 1c has a thickness d4, a radius of curvature r on the object side, and a radius of curvature r on the image side.
5 is a meniscus lens. Lens 1b and lens 1c
Is zero.

The second lens group 2 includes three lenses 2a and 2a.
b, 2c, a lens group having a negative refractive power and having a zooming effect by moving on the optical axis. The lens 2a is a meniscus lens which is located rearward of the lens 1c by a variable air distance d5, has a thickness d6, a curvature radius r6 on the object side surface, and a curvature radius r7 on the image surface side. Lens 2b
The object side surface is a concave lens having a thickness d8, a curvature radius r8 of the object side surface, and a curvature radius r9 of the image side on the optical axis at a distance from the lens 2a and the air gap d7. The lens 2c is in close contact with the lens 2b, has a thickness d9, and a radius of curvature r of the object side surface.
9. A spherical lens having a radius of curvature r10 on the image plane side.

The third lens group 3 is composed of only one lens 3a and is an aspheric lens having a positive refractive power. Third
The lens group 3 is a fixed group of lenses that has a light condensing function. The lens 3a is located rearward of the lens 2c by a variable air distance d10, has a thickness d11, a radius of curvature r11 of the object side surface,
The lens has a radius of curvature r12 on the image plane side.

The fourth lens group 4 includes three lenses 4a, 4a
b, 4c, a lens group having a positive refractive power and performing focus adjustment by moving on the optical axis. The fourth lens group 4 has a relatively large air gap d12 with the third lens group 3. The lens 4a has a thickness d13,
The spherical lens has a radius of curvature r13 on the object side surface and a radius of curvature r14 on the image surface side. The lens 4b is mounted in close contact with the lens 4a, and has a thickness d14, a radius of curvature r14 of the object side surface,
This is an aspheric lens having a curvature radius r15 on the image plane side. The lens 4c is a spherical lens having a thickness d16, a radius of curvature r16 on the object side surface, and a radius of curvature r17 on the image surface side, with the air interval d15 on the optical axis being 0 and the lens 4b being in contact with the lens 4b.

FIG. 2 shows a configuration diagram of such an aspherical zoom lens. Here, the same reference numerals as in FIG. 1 are assigned to the respective lenses, and the lens configuration will be described. That is, the first lens group 1 is composed of, in order from the object side, spherical lenses 1a and 1b and a meniscus lens 1c having a positive refractive power. The second lens group 2 includes a lens having at least one or more aspherical shapes,
It is composed of a meniscus lens 2a having a negative refractive power and cemented lenses 2b and 2c. The third lens group 3 is composed of a lens 3a having at least one aspheric surface. Furthermore, the fourth
The lens group 4 includes two lenses 4a and 4b including a lens having at least one or more aspherical shapes,
It may be constituted by a convex lens 4c.

To make a zoom lens compact, it is necessary to increase the refractive power of each lens unit. Here, the following conditions are considered. (1) f1 / fW (2) | f2 | / fW (3) f3 / fW (4) f4 / fW (5) BF / fW (6) d12 / f4 (7) r11 / f3 (8) | r13 | / F4 (9) | r17 | / f4 where fi is the focal length of the i-th lens group (i = 1, 2, 2,
3, 3, 4) fw: focal length of the zoom lens at the wide angle BF: distance from the last lens surface to the imaging surface 7 in air

The above conditions (1), (2), (3), and (4) are conditional expressions for defining the refractive power of each lens unit, and provide a strong refractive power for realizing miniaturization. In addition, there is a range where satisfactory aberration performance is satisfied by optimally setting the lens type, surface shape, and the like of each lens group.

On the other hand, when the third lens group 3 is an aspherical lens having a convex surface facing the object side, the third lens group is constituted by a single lens and has a large aperture of about 1.6 in F number. This is indispensable for correcting aberration. Especially the third
The aspherical shape of the lens group 3 has a great effect on correcting spherical aberration. The fourth lens group 4 is composed of a cemented lens having two lenses and one convex lens and having at least one aspherical surface realizes a long back focus BF and has a small number of components of three. Thus, it is indispensable to correct on-axis and off-axis chromatic aberrations, correct monochromatic off-axis aberrations, particularly coma, and loosen tolerances in the assembly process. Here, each condition described above will be described in more detail.

Condition (1) relates to the refractive power of the first lens group 1. If the value of the expression (1) is below a certain lower limit, the refractive power of the first lens group 1 becomes too large, so that it becomes difficult to correct spherical aberration on the long focal length side. If the value of the expression (1) exceeds a certain upper limit, the lens length increases, and a compact zoom lens cannot be realized.

The condition (2) is a condition relating to the refractive power of the second lens group 2. When the value of equation (2) deviates from a certain lower limit, the lens group can be made compact, but the Petzval sum of the entire system becomes significantly negative, and the field curvature cannot be corrected only by selecting the glass material. If the value of the expression (2) exceeds a certain upper limit, aberration correction is easy, but the zooming system becomes long and the whole system cannot be made compact.

The condition (3) is a condition relating to the refractive power of the third lens group 3. If the value of the expression (3) exceeds a certain lower limit, the refractive power of the third lens group 3 becomes too large, so that a back focus length in which the color separation optical system 5 can be inserted cannot be realized, and it is difficult to correct spherical aberration. Become. If the value of the expression (3) exceeds a certain upper limit, the first lens group 1, the second lens group 2,
Since the combining system of the third lens group 3 is a diverging system, it is not necessary to reduce the lens outer diameter of the fourth lens group 4 located thereafter. Further, the Petzval sum of the entire system cannot be reduced.

Condition (4) relates to the refractive power of the fourth lens unit 4. If the value of the expression (4) deviates from a certain lower limit, the screen coverage range becomes narrower, and it is necessary to increase the lens diameter of the first lens group 1 to obtain a desired range, so that reduction in size and weight cannot be realized. When the value of equation (4) exceeds a certain upper limit, aberration correction is easy, but the fourth
The amount of movement of the lens group 4 becomes large, so that not only the entire system cannot be made compact, but also it becomes difficult to correct the imbalance of off-axis aberrations at the time of short-range shooting and long-range shooting.

Condition (5) is a conditional expression relating to the back focus length. If the value of equation (5) is below a certain lower limit, it is not possible to insert a color separation optical system 5 having a sufficient length for sufficient color separation. If the value of equation (5) exceeds a certain upper limit, compactness cannot be achieved.

Condition (6) is a conditional expression relating to the air gap between the third lens unit 3 and the fourth lens unit 4. If the value of the expression (6) exceeds a certain lower limit, the off-axis ray height becomes small, and it becomes difficult to correct lateral chromatic aberration only by selecting a glass material. In addition, the amount of movement of the fourth lens unit 4 during short-range shooting is restricted, and a sufficient close-up range cannot be realized. If the value of equation (6) exceeds a certain upper limit, it is difficult to make the entire system compact. In order to secure a sufficient amount of light around the screen, the fourth lens group 4
Lens outer diameter cannot be reduced.

The condition (7) relates to the radius of curvature of the object side surface of the aspherical lens constituting the third lens unit 3.
By introducing an aspherical surface on one or both of the object side surface and the image side surface and optimally setting the shape, various aberrations can be well corrected in spite of a single lens. However, if the value of equation (7) exceeds a certain lower limit, it becomes difficult to correct spherical aberration, and if the value of equation (7) departs from a certain upper limit, it is difficult to correct coma for off-axis rays below the principal ray. Becomes

Condition (8) relates to the radius of curvature of the concave surface of the concave lens constituting the fourth lens unit 4 on the object side surface.
If the value of the expression (8) deviates from a certain lower limit, the angle of incidence on these surfaces becomes large, and it becomes difficult to correct coma for off-axis rays below the principal ray. When the value exceeds a certain upper limit, the refractive power of the concave lens cannot be increased, and a sufficient back focus cannot be obtained.

Condition (9) is a condition for the second lens group 4
It relates to the radius of curvature of the image side surface of the convex lens located on the image side among the convex lenses. When the value of the expression (9) deviates from a certain lower limit, the exit angle from these surfaces increases,
It becomes difficult to correct coma for off-axis rays above the principal ray and to correct distortion on the wide-angle side. If the value of the expression (9) exceeds a certain upper limit, the refractive power of the intermediate convex lens becomes large, so that a sufficient back focus cannot be obtained.

Next, Table 1 shows specific numerical examples of the aspherical zoom lens of the first embodiment.

[Table 1] In Table 1, the numbers in the first column indicate the lens groups,
The number j in the second column is the radius of curvature rj (j of each lens shown in FIG.
= 1 to 20), which is the j-th surface. In the following columns, r is the radius of curvature of each lens surface, d is the thickness of each lens or the air gap between lenses, n is the refractive index of each lens for d-line, and ν is the Abbe number of each lens for d-line. is there.

The aspheric shape is defined by the following equation.

(Equation 1) Here, Z: the distance from the aspherical vertex of the point on the aspherical surface at the height Y from the optical axis Y: the height from the optical axis C: the curvature of the aspherical vertex (= 1 / r) D, E, F, G: Aspheric coefficient K: Conical constant

The first surface, the eleventh surface, the twelfth surface, the fifteenth surface
The surface is aspherical, and the aspherical coefficients are shown in Table 2 below.

[Table 2] In Table 2, the first line is the radius of curvature r1, r11, r1.
The numbers of the lens surfaces of the lenses 1a, 3a, and 4b having 2, r15 are shown.

Next, Table 3 shows the case where the object point is adjusted to infinity by zooming of the aspherical zoom lens of this embodiment. In Table 3, when the aspherical zoom lens is set at the wide-angle end, the standard, and the telephoto end, the focal length at the wide-angle end of the entire lens system is f, and the F number at the telephoto end is F / NO. The value of d has been calculated by simulation.

[Table 3]

Table 4 shows a case where the object point was measured from the front end of the aspherical zoom lens by zooming and adjusted to a position of 2 m. The numerical values in Table 4 are displayed in the same format as in Table 3.

[Table 4]

Similarly, Table 5 shows a case where the object point was measured from the front end of the aspherical zoom lens by zooming and adjusted to a position of 1 m.

[Table 5]

In Tables 3 to 5, the air distance d12 at the standard position is smaller than the other distances, and is the zoom position where the fourth lens group 4 comes closest to the third lens group 3 at each object point position.

In the case of having the above numerical values, formula (1)
The value of equation (9) was determined, and the results are shown in Table 6.

[Table 6]

Next, an aspherical zoom lens according to a second embodiment of the present invention will be described. The configuration of the aspherical zoom lens of the second embodiment is the same as that shown in FIG.
3a and 4b were aspherical lenses, respectively, and the values of the radius of curvature r, the thickness, and the air gap d of each lens constituting each lens group were changed and evaluated. These values are shown in Table 7 in the same format as in Table 1.

[Table 7]

The third, eleventh, twelfth, and fifteenth surfaces
The surfaces are aspherical, and their aspherical coefficients are shown in Table 8 in the same format as in Table 2.

[Table 8]

Next, as an example of the variable air gap by zooming of the aspherical zoom lens of the present embodiment, Table 2 shows a case where the object point is measured from the front end of the lens and the position is adjusted to 2 m.

[Table 9]

In the case of having such numerical values, equations (1) to
The value of equation (9) was determined, and the results are shown in Table 10.

[Table 10]

Next, an aspherical zoom lens according to a third embodiment of the present invention will be described. The configuration of the aspherical zoom lens of the third embodiment is the same as that shown in FIG.
3a and 4b were aspherical lenses, respectively, and the values of the radius of curvature r, the thickness, and the air gap d of each lens constituting each lens group were changed and evaluated. These values are shown in Table 11.

[Table 11]

The fourth, eleventh, twelfth, and fifteenth surfaces
The surface is aspherical, and the aspherical surface coefficients are shown in Table 12.

[Table 12]

Next, as an example of a variable air gap by zooming of the aspherical zoom lens of this embodiment, a case where the object point is measured from the front end of the lens and adjusted to a position of 2 m is shown in Table 13.
Shown in

[Table 13]

In the case of having such numerical values, equations (1) to
The value of equation (9) was determined, and the results are shown in Table 14.

[Table 14]

Next, an aspherical zoom lens according to a fourth embodiment of the present invention will be described. The configuration of the aspherical zoom lens of the fourth embodiment is the same as that shown in FIG.
1b, 3a, and 4b were aspherical lenses, respectively, and evaluated by changing the values of the radius of curvature r, the thickness, and the air gap d of each lens constituting each lens group. Table 15 shows these values.

[Table 15]

The first, third, eleventh, and twelfth surfaces
The fifteenth surface is an aspheric surface, and the aspheric surface coefficients are shown in Table 16.

[Table 16]

Next, as an example of a variable air gap by zooming of the aspherical zoom lens of this embodiment, a case where an object point is measured from the front end of the lens and adjusted to a position of 2 m is shown in Table 17.
Shown in

[Table 17]

In the case of having such numerical values, equations (1) to
The value of equation (9) was determined, and the results are shown in Table 18.

[Table 18]

Next, an aspheric lens according to a fifth embodiment of the present invention will be described. The configuration of the aspherical lens of the fourth embodiment is also the same as that shown in FIG. 1. The lenses 3a and 4b are aspherical lenses, respectively, and the radii of curvature r, wall thickness, and air of each lens constituting each lens group. The value of the interval d was changed and evaluated. These values are shown in Table 19.

[Table 19]

The eleventh, twelfth, and fifteenth surfaces are aspherical, and the aspherical coefficients are shown in Table 20.

[Table 20]

Next, as an example of a variable air gap by zooming of the aspherical zoom lens of this embodiment, a case where the object point is measured from the front end of the lens and adjusted to a position of 2 m is shown in Table 21.
Shown in

[Table 21]

In the case of having such numerical values, equations (1) to
The value of equation (9) was determined, and the results are shown in Table 22.

[Table 22]

Finally, an aspheric lens according to a sixth embodiment of the present invention will be described. The configuration of the aspherical lens of the sixth embodiment is the same as that shown in FIG. 2, and the lenses 2b, 3a, 4b
Were aspherical lenses, and the values of the radius of curvature r, the thickness, and the air gap d of each lens constituting each lens group were changed and evaluated. Table 23 shows these values.

[Table 23]

The eighth, eleventh, twelfth, and fifteenth surfaces
The surface is aspherical, and the aspherical surface coefficients are shown in Table 24.

[Table 24]

Next, as an example of a variable air gap by zooming of the aspherical zoom lens of this embodiment, a case where the object point is measured from the front end of the lens and adjusted to a position of 2 m is shown in Table 25.
Shown in

[Table 25]

In the case of having such numerical values, equations (1) to
The value of equation (9) was determined, and the results are shown in Table 26.

[Table 26]

In the aspherical zoom lenses of the first to sixth embodiments designed as described above, five aberrations for which the characteristics of the lens system are evaluated will be described. 3 to 20 are explanatory diagrams showing aberrations of the aspherical smooth lens. In each of the drawings, (a) is spherical aberration, (b) is astigmatism, (c) is distortion, and (d) is axial chromatic aberration. And (e) are graphs showing chromatic aberration of magnification.

In (a) of each figure, the abscissa indicates the aberration (mm) from the ideal image plane, and the ordinate indicates the pupil height of the on-axis ray by F number. The solid curve represents the characteristic for the d-line, and the dotted line represents the sine condition. The sine condition means that when a spherical aberration is removed from a set of conjugate points on the axis of the optical system, a small area perpendicular to the axis passing through these conjugate points is imaged without aberration. Is a necessary condition.

In (b) of each figure, W on the vertical axis is the intersection angle between the optical axis of the object point and the central axis of the lens. The solid curve indicates sagittal field curvature, and the dotted curve indicates meridional field curvature. In (c), the horizontal axis represents the distortion rate when the rectangular object is distorted into a barrel or pincushion.
In (d) and (e), the solid curve is the d-line, the dotted curve is the F-line, and the dashed curve (sometimes overlapped with the solid line) is the chromatic aberration with respect to the C-line.

FIGS. 3, 4 and 5 are aberration diagrams of the aspherical zoom lens of the first embodiment shown in Table 1 at the wide-angle end, the standard position, and the telephoto end, respectively. Similarly, FIGS. 6, 7, and 8
9A and 9B are aberration diagrams of the aspherical zoom lens of the second example shown in Table 7, respectively. FIGS. 9, 10 and 11 are aberration diagrams of the aspherical zoom lens of the third embodiment shown in Table 11. FIGS. 12, 13 and 14 are aberration diagrams of the aspherical zoom lens of the fourth embodiment shown in Table 15, respectively. FIGS. 15, 16 and 17 are aberration diagrams of the aspherical zoom lens of the fifth embodiment shown in Table 19, respectively. 18 and 19,
FIG. 20 is an aberration diagram of the aspherical zoom lens of the sixth example shown in Table 23.

Judging from these FIGS. 3 to 20, it can be seen that the aspherical zoom lens of each embodiment has good optical performance. Also, since these aspherical zoom lenses have a long back focus BF, a space for installing a color separation optical system 5 between the fourth lens group 4 and the image plane 7 as shown in FIG. The color separation optical system 5 of a three-plate type, which can be made sufficiently large, is composed of a prism, and is larger than a single-plate type, can be provided. And CCD
A three-panel type with excellent performance by integrating a mechanism that inputs pixel signals output from an image sensor such as a video signal into a signal processing circuit and records a video signal on a recording medium, and a viewfinder that monitors an image field of view. Video camera can be realized.

[0064]

As described above , according to the first to sixth aspects of the present invention,
For example , a high-performance aspherical zoom lens having an F-number of about 1.6 and a zoom ratio of about 10 times and having a long back focus can be realized, and the total number of lenses constituting each lens group can be realized. Can be realized with a configuration as small as ten, and a compact, lightweight, and high-performance zoom lens can be obtained.

According to the seventh aspect of the present invention , a small, lightweight and high-performance three-plate video camera can be realized by using this aspherical zoom lens.

[Brief description of the drawings]

FIG. 1 is a lens arrangement diagram illustrating a configuration of an aspherical zoom lens according to first to fifth embodiments of the present invention.

FIG. 2 is a lens arrangement diagram showing a configuration of an aspherical zoom lens according to a sixth embodiment of the present invention.

FIG. 3 is an aberration diagram at a wide-angle end of the aspherical zoom lens according to the first example.

FIG. 4 is an aberration diagram at a standard point of the aspherical zoom lens according to the first example.

FIG. 5 is an aberration diagram at a telephoto end of the aspherical zoom lens according to the first example.

FIG. 6 is an aberration diagram at a wide-angle end of an aspherical zoom lens according to a second example.

FIG. 7 is an aberration diagram at a standard point of the aspherical zoom lens according to the second example.

FIG. 8 is an aberration diagram at a telephoto end of an aspherical zoom lens according to a second example.

FIG. 9 is an aberration diagram at a wide-angle end of the aspherical zoom lens according to Example 3;

FIG. 10 is an aberration diagram at a standard point of the aspherical zoom lens according to the third example.

FIG. 11 is an aberration diagram at a telephoto end of the aspherical zoom lens according to Example 3;

FIG. 12 is an aberration diagram at a wide-angle end of an aspherical zoom lens according to a fourth example.

FIG. 13 is an aberration diagram at a standard point of the aspherical zoom lens according to the fourth example.

FIG. 14 is an aberration diagram at a telephoto end of an aspherical zoom lens according to a fourth example.

FIG. 15 is an aberration diagram at a wide-angle end of an aspherical zoom lens according to a fifth example.

FIG. 16 is an aberration diagram at a standard point of the aspherical zoom lens of the fifth example.

FIG. 17 is an aberration diagram at a telephoto end of the aspherical zoom lens of Example 5;

FIG. 18 is an aberration diagram at a wide-angle end of the aspherical zoom lens according to the sixth example.

FIG. 19 is an aberration diagram at a standard point of the aspherical zoom lens in the sixth example.

FIG. 20 is an aberration diagram at a telephoto end of an aspherical zoom lens according to a sixth example.

FIG. 21 is a lens arrangement diagram showing a configuration of a conventional zoom lens.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 1st lens group 1a-1c, 2a-2c, 3a, 4a-4c Lens 2 2nd lens group 3 3rd lens group 4 4th lens group 5 Color separation optical system 6 Face plate 7 Imaging surface

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-5-72474 (JP, A) JP-A-6-265786 (JP, A) JP-A-6-347697 (JP, A) (58) Field (Int.Cl. ⁷ , DB name) G02B 9/00-17/08 G02B 21/02-21/04 G02B 25/00-25/04

Claims (7)

(57) [Claims] 1. A first lens unit having a positive refractive power and fixed to an image plane, and a second lens unit having a negative refractive power and having a zooming effect by moving on an optical axis in order from the object side. A lens group, a third lens group having a positive refractive power fixed to the image plane and having a condensing action, and an image plane that fluctuates due to the movement of the second lens group and the movement of the object are placed at a fixed position from the reference plane. A fourth lens group having a positive refractive power that moves on the optical axis to maintain
Wherein the third lens group and the fourth lens group have an air gap, and the first lens group includes a concave lens, a convex lens, and a meniscus convex lens in order from the object side. Wherein the second lens group includes a meniscus concave lens , a biconcave lens, and a convex lens; the third lens group includes a lens having at least one aspheric surface; and the fourth lens group includes: It is configured to include a lens having at least one aspherical surface, a cemented lens having two lenses, and one convex lens , where fW is a focal length at a wide-angle end, and fi (i = 1, 2, 2).
3, 4) are the focal length of the i-th lens group, and BF is in air.
At the distance from the lens final surface to the image forming surface, d12
An air gap between the third lens group and the fourth lens group,
r11 is the object side of the convex lens constituting the third lens group
The radius of curvature of the surface, r13, is
The radius of curvature of the surface of the compound lens closest to the object, r17, is
The radius of curvature of the image side surface of the convex lens constituting the fourth lens group
To time, (1) 5.5 <f1 / fW <6.3 (2) 1.0 <| f2 | / fW <1.2 (3) 5.3 <f3 / fW <6.2 (4) 3.0 <f4 / fW <3.3 (5) 3.2 <BF / fW <4.2 (6) 0.1 <d12 / f4 <0.4 (7) 0.5 <r11 / f3 < 0.9 (8) 1.1 <| r13 | / f4 <2.4 (9) An aspherical zoom lens that satisfies 0.6 <| r17 | / f4 <0.8 . 2. A first lens unit having a positive refractive power and fixed with respect to an image plane, and a second lens unit having a negative refractive power and having a zooming effect by moving on an optical axis in order from the object side. A lens group, a third lens group having a positive refractive power fixed to the image plane and having a condensing action, and an image plane that fluctuates due to the movement of the second lens group and the movement of the object are placed at a fixed position from the reference plane. A fourth lens group having a positive refractive power that moves on the optical axis to maintain
Wherein the third lens group and the fourth lens group have an air gap, and the first lens group has a concave lens, a convex lens , a meniscus convex lens, and at least one lens in order from the object side. is configured to include a lens having a surface or aspherical, the second lens group is configured to include a meniscus concave lens and a biconcave lens and a convex lens, the third lens group, at least one surface is aspherical single The fourth lens group includes a lens having at least one aspheric surface, a cemented lens having two lenses, and one convex lens , and fW is a focal length at a wide-angle end. , Fi (i = 1, 2, 2)
3, 4) are the focal length of the i-th lens group, and BF is in air.
At the distance from the lens final surface to the image forming surface, d12
An air gap between the third lens group and the fourth lens group,
r11 is the object side of the convex lens constituting the third lens group
The radius of curvature of the surface, r13, is
The radius of curvature of the surface of the compound lens closest to the object, r17, is
The radius of curvature of the image side surface of the convex lens constituting the fourth lens group
When, (1) 3.0 <f1 / fW <8.0 (2) 0.5 <| f2 | / fW <1.6 (3) 5.3 <f3 / fW <7.0 (4) 2.0 <f4 / fW <5.0 (5) 1.5 <BF / fW <5.0 (6) 0.02 <d12 / f4 <1.0 (7) 0.3 <r11 / f3 < 1.5 (8) 0.3 <| r13 | / f4 <3.0 (9) An aspherical zoom lens characterized by satisfying 0.3 <| r17 | / f4 <1.5 , respectively . 3. An image surface having a positive refractive power in order from the object side.
1st lens group fixed with respect to light with negative refractive power
Second lens having zooming effect by moving on axis
Positive refractive power fixed to the group and the image plane and having a condensing effect
The third lens group, the movement of the second lens group, and the
The image plane that fluctuates due to movement is kept at a fixed position from the reference plane.
A fourth lens group having a positive refractive power that moves on the optical axis
A aspheric zoom lens comprising, said third lens group and the fourth lens group have a air gap
And, wherein the first lens group, a concave lens and a convex lens from the object side
And the second lens group includes a meniscus concave lens and a biconcave lens.
And a convex lens, and at least one aspheric surface
It is configured to include a lens, the third lens group, at least one surface is aspherical Les
Is configured to include a lens, the fourth lens group has at least one surface or aspherical
, A two-element cemented lens and one convex
Is configured to include a lens, the focal length at the wide angle end to fW, fi (i = 1,2,
3, 4) are the focal length of the i-th lens group, and BF is in air.
At the distance from the lens final surface to the image forming surface, d12
An air gap between the third lens group and the fourth lens group,
r11 is the object side of the convex lens constituting the third lens group
The radius of curvature of the surface, r13, is
The radius of curvature of the surface of the compound lens closest to the object, r17, is
The radius of curvature of the image side surface of the convex lens constituting the fourth lens group
When, (1) 3.0 <f1 / fW <8.0 (2) 0.5 <| f2 | / fW <1.6 (3) 5.3 <f3 / fW <7.0 (4) 2.0 <f4 / fW <5.0 (5) 1.5 <BF / fW <5.0 (6) 0.02 <d12 / f4 <1.0 (7) 0.3 <r11 / f3 < 1.5 (8) 0.3 <| r13 | / f4 <3.0 (9) An aspherical zoom lens characterized by satisfying 0.3 <| r17 | / f4 <1.5 , respectively . 4. The third lens group has a convex surface facing the object side.
Aspherical single lens with positive refractive power
The aspherical zoom lens according to claim 1 . 5. The fourth lens group includes, in order from the object side,
Two-element cemented lens, convex lens with convex surface facing the image side
And at least one surface has an aspherical shape.
The method according to any one of claims 1 to 3, wherein
Aspherical zoom lens. 6. An image surface having a positive refractive power in order from the object side.
1st lens group fixed with respect to light with negative refractive power
Second lens having zooming effect by moving on axis
Positive refractive power fixed to the group and the image plane and having a condensing effect
The third lens group, the movement of the second lens group, and the
The image plane that fluctuates due to movement is kept at a fixed position from the reference plane.
A fourth lens group having a positive refractive power that moves on the optical axis
A aspheric zoom lens comprising, said third lens group and the fourth lens group have a air gap
And, wherein the first lens group, a concave lens and a convex lens from the object side
Lens and meniscus convex lens, and at least one
It is configured to include a lens having a spherical shape, the second lens group, a meniscus concave lens and a biconcave lens
And the third lens group includes a single lens having at least one aspheric surface.
The fourth lens group is configured to include at least one aspheric surface.
, A two-element cemented lens and one convex
Is configured to include a lens, the focal length at the wide angle end to fW, fi (i = 1,2,
The 3,4) focal length of the i-th lens group, the distance BF from the last lens surface in air to the imaging plane, the d12
Air space between the fourth lens group and the third lens group,
r11 the radius of curvature of the object side surface of the convex lens constituting the third lens group, and most surface of the from the object of the radius of curvature of the cemented lens constituting the fourth lens group r13, the <br/> fourth lens r17 Assuming that the radius of curvature of the image side surface of the convex lens constituting the group is: (1) 5.5 <f1 / fW <6.3 (2) 1.0 <| f2 | / fW <1.2 (3) 3 <f3 / fW <6.2 (4) 3.0 <f4 / fW <3.3 (5) 3.2 <BF / fW <4.2 (6) 0.1 <d12 / f4 <0. 4 (7) 0.5 <r11 / f3 <0.9 (8) 1.1 <| r13 | / f4 <2.4 (9) 0.6 <| r17 | / f4 <0.8 respectively satisfying An aspherical zoom lens. 7. The non-sphere according to any one of claims 1 to 6.
A surface zoom lens, a color separation optical system that splits the output light of the aspherical zoom lens into R, G, and B wavelength bands, and R, G, and B wavelength bands that are split by the color separation optical system And a plurality of image sensors that convert the image of the image into pixel signals.