JPH0961707A - Standard lens system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a standard lens system for photographing lens and electronic video apparatus having high depiction performance by improving sagittal comatic aberrations and curvature of field to meet a trend toward a larger aperture diameter. SOLUTION: This standard lens system consists of a positive first lens group G1, a diaphragm, a positive second lens group G2 and a negative third lens group G3. The first lens group G1 includes at least one element of a positive meniscus lens of which the convex face is directed to an object side and the second lens group G2 included at least one set of the combined lens of a negative lens and a positive meniscus lens. The third lens group G3 is a lens system including at least one element of positive lens and negative lens. The purposes are achieved by adequately arranging the refracting power of the lens groups.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a large-aperture-ratio standard lens having high drawing performance.

[0002]

2. Description of the Related Art In a so-called standard lens having an angle of view of about 46 °, an image forming lens for a single-lens reflex camera is of a deformed Gauss type which is asymmetrical when viewed from the refractive power arrangement because of the necessity of providing a mirror movable space. It was adopted to secure the back focus. However, such a lens system having an asymmetrical refractive power arrangement causes deterioration of various off-axis aberrations. In particular, as the aperture ratio increases, chromatic aberration of magnification, field curvature, sagittal coma and the like tend to become more prominent. Furthermore, there is a limit in trying to correct coma by increasing the refractive index of glass, and chromatic aberration and field curvature become problems.

On the other hand, a camera having a range finder has a loose back focus, but a lens system used for this is actually a Gaussian type having many cemented surfaces.

Further, US Pat. No. 5,299,065 discloses a lens system for a night vision device, which has an angle of view of 40 ° and an aperture ratio of 1: 1.2. However, this lens system
Distortion aberration is extremely large due to the asymmetric lens configuration. The lens system described in German Patent No. 1286776 is also an optical system for night-vision devices, in which a lens group having a meniscus lens with a concave surface facing the image side is arranged in the rear. These lens systems need to have a large diameter in order to compensate for the lack of light quantity, and the wavelength range used is also limited.

Further, the lens system described in Japanese Patent Publication No. 39-22079 and Japanese Patent Publication No. 45-14839 is a copying lens for finite distance photography and is used at a specific magnification. Different from a lens.

[0006]

SUMMARY OF THE INVENTION The present invention is directed to a general photographic lens that uses the entire visible range and a standard lens for an optical system for electronic image equipment, and sagittal coma aberration and a sagittal coma aberration even when the aperture ratio is increased. It is an object of the present invention to provide an optical system which has improved field curvature and has high drawing performance.

[0007]

A lens system to which the present invention is directed is a lens group composed of a positive lens and a negative lens having a relatively small refractive power behind a modified Gauss type converging system including an aperture stop. Is arranged. The lens system of the present invention having such a configuration not only removes the limitation of the back focus of the conventional lens system, but also utilizes the portion that is originally a space to flatten the off-axis image surface. This is an improvement in performance, which allows it to have a unique optical arrangement that could not be realized with a lens system used in the visible range.

A lens system in a so-called standard system having an angle of view of about 40 ° to 52 ° is generally required to have a large aperture. Therefore, the modified Gaussian type, which has a proven record in the past, is desirable in that the lens system can be configured easily from the passing state of the light flux. However, since the Gauss type lens system has a symmetrical basic configuration, the principal point position is near the central aperture stop, and when this is used for a single-lens reflex, as a result, the refractive power arrangement becomes asymmetric. , This leaves some dissatisfaction with the opening performance.

In the present invention, it is assumed that the back focus is loosely restricted, and thereby the refracting power arrangement is made more symmetrical. On the other hand, with a photographic lens that requires good correction of aberrations from an object point at infinity to a finite object point, it is not possible to give strict symmetry to the refractive power arrangement, but off-axis coma aberration, chromatic aberration of magnification, Correction of distortion is extremely easy. On the other hand, the conventional standard lens has a relatively remarkable field curvature. The present invention has the following configuration aiming at correcting this field curvature.

That is, the lens system of the present invention comprises, in order from the object side, a first lens group having a positive refractive power, a second lens group having a positive refractive power with an aperture stop interposed therebetween, and a second lens group having a negative refractive power. It is configured by three basic lens groups of three lens groups, and further, the first lens group includes at least one positive meniscus lens having a convex surface facing the object side, a positive meniscus lens, and at least one set of negative lenses. The second lens group has at least one set of a negative lens and a positive lens cemented with a doublet and a positive lens, and the third lens group has at least one positive lens and a negative lens. The standard lens system satisfies the following conditions (1) to (4) at the same time.

(1) 2.0 <f ₁ / f <10 (2) 1.0 <f ₁ / f ₂ <8 (3) 0.8 <β ₃ <1.3 (4) 0.1 < f _b /f<0.5 where f ₁ is the focal length of the first lens group, f ₂ is the focal length of the second lens group, f is the focal length of the entire system, and β ₃ is the third lens at infinity. The image forming magnification of the group, f _b, is the back focus of the entire system.

In the lens system having the above structure, the first lens group and the second lens group, which are arranged with the diaphragm interposed therebetween, are:
Since it is originally a convergent system, it is natural for both lens groups to have a positive refractive power, and in order to take advantage of the symmetry of the lens configuration, it is necessary to use a lens system with the above-mentioned refractive power arrangement for aberration. It is clear in principle that the correction is desirable. Further, in order to maintain the flatness of the off-axis image surface, that is, in order to correct the field curvature, in consideration of the downsizing of the lens system, the refractive power of the third lens group having a negative refractive power is reduced. It is preferable. From these points, the present invention comprises, in order from the object side as described above, the first lens group having a positive refractive power, the second lens group having a positive refractive power, and the third lens group having a negative refractive power. , The first lens group and the second lens group are configured to be nearly symmetrical to realize image plane correction.

The condition (1) defines the refractive power of the first lens group. This condition differs from the refractive power arrangement of the conventional lens system for single-lens reflex lenses in that the first lens group has a symmetrical refractive power. This is an important condition for getting close to the force distribution.

When the lower limit of 2.0 of the condition (1) is exceeded, it is preferable for the purpose of downsizing the lens system.
The refracting power of the lens group becomes large, making it difficult to correct field curvature and coma. Although it may be advantageous for aberration correction for a specific finite object point, it is not desirable in the shooting distance range used. On the other hand, when the upper limit of 10 is exceeded, it is advantageous in terms of aberration correction, but the lens system becomes large, which is not preferable. In addition, the symmetry defined by the condition (2) collapses and the refractive power arrangement of the single-lens reflex lens system is approached, which tends to increase the asymmetrical aberration.

The condition (2) defines the ratio of the focal lengths of the first lens group and the second lens group having a positive refractive power. This represents a symmetry factor, and is for determining the refractive power of the second lens group when the refractive power of the first lens group is determined.

When the lower limit of 1.0 of the condition (2) is exceeded,
While the symmetry of the refractive power with respect to the aperture stop becomes strong, appropriate aberration correction cannot always be obtained near infinity. That is, it means that it is not always good to have perfect symmetry in the case of a lens system such as a photographic lens that is used by focusing in a wide range. When the upper limit of 8 of the condition (2) is exceeded, asymmetry becomes strong, and coma aberration, astigmatism, chromatic aberration of magnification, etc. remain large.

The condition (3) defines the image forming magnification of the third lens group. When the lower limit value of 0.8 is exceeded, it is advantageous for aberration correction, but when the aperture is increased, the lens system is enlarged. However, the desired results cannot be obtained due to the large size. When the upper limit of 1.3 is exceeded, the combined focal length of the first lens group and the second lens group becomes large, making it difficult to correct aberrations, and at the same time, in proportion to the square of the magnification β ₃ of the third lens group. The longitudinal aberration may change, and it becomes difficult to balance the large aperture and the small size.

The condition (4) defines the range in which the lens system of the present invention is used, by direct back focus. When the upper limit of 0.5 of the condition (4) is exceeded, the lens system approaches a single-lens reflex lens system and deviates from the spirit of the present invention. Further, the refractive power arrangement also becomes asymmetrical, which is not preferable. On the other hand, when the lower limit of 0.1 is exceeded, the back focus becomes extremely short, the image formation by stray light increases, and the lens outer diameter increases, which is not desirable in terms of mechanism and driving.

Next, the lens system of the present invention will be specifically described. In FIG. 1, a cross-sectional view and an optical path of Example 1 shown later are drawn. As shown in this figure, the lens system of the present invention comprises three lens groups G1, G2, G3, of which the front side is the first lens group G1, the back side is the second lens group G2, and the rear side thereof is behind the aperture stop. At a specific interval to the third
The lens group G3 is arranged. Of these lens groups, the first and second lens groups G1 and G2, which are main lens systems, form a converging system, and the third lens group G3 is an optical system for image plane correction.

Table 1 below shows aberration coefficients at infinity of the lens system of Example 1 described later.

Table 1 SA ₃ SA ₅ CM ₃ CM ₅ AS ₃ AS ₅ G1 0.61592 0.27272 -0.63433 0.1169 0.12398 0.05623 G2 -0.53235 -0.18676 -0.18712 -0.35025 -0.50777 -0.16709 G3 -0.12537 -0.04311 0.75385 0.29389 0.40822 0.11745 Σ 0.04286 -0.0676 0.06054 0.02443 0.00659 DT ₃ PT ₃ G1 1.11833 0.18114 G2 -1.76827 -0.65002 G3 0.89593 0.34986 Σ 0.24599 -0.11902 As is clear from Table 1 above, spherical aberration has a large aberration coefficient on a surface with a large entrance or exit tilt angle. In the above lens system, the first lens group G1 is overcorrected, which is balanced due to the undercorrection of the second lens group G2.
The lens group G3 is used for compensation. This effect is the same for the higher-order aberration coefficient.

On the other hand, with respect to off-axis aberrations such as coma, astigmatism, and distortion, the air lens surface in the first lens group G1 serves as an aberration generating surface, and the aberrations on these surfaces cancel each other out. With respect to astigmatism and distortion, the first lens group G1 mutually corrects the lens groups by the same action as with spherical aberration, and the higher-order aberration coefficient also has the same action.

On the other hand, coma is characterized in that the action of the third-order aberration coefficient and the action of the higher-order aberration coefficient have somewhat different actions.

Within the range of the third-order coma aberration coefficient, the first lens group and the second lens group are undercorrected, and this is compensated for by the third lens group. On the other hand, the fifth-order coma aberration coefficient is different in that the first lens group has an effect of overcorrection. As described above, the third lens group as a whole compensates for off-axis aberrations by overcorrecting.

The present invention also relates to the first lens group as described above,
It is composed of three basic lens groups, that is, a second lens group and a third lens group, and each lens group has the structure already described. At the time of focusing, the three lens groups are moved to the object side and at least Another purpose is to realize a lens system in which the variation in aberration is corrected by changing the spacing in the second lens group and the spacing in the third lens group.

That is, according to the present invention, in order from the object side, the first lens group having a positive refractive power, the second lens group having a positive refractive power across the aperture stop, and the third lens group having a negative refractive power. The first lens group includes at least one positive meniscus lens having a convex surface directed toward the object side, at least one set of meniscus lenses and a doublet including a negative lens, and the second lens group includes at least one. It has a doublet and a positive lens cemented with a set of a negative lens and a positive lens, and the third lens group is composed of at least one positive lens and a negative lens, and focuses from an infinite object point to a finite object point. At that time, the first lens group based on the object point position at infinity,
The standard lens system is characterized in that the second lens group and the third lens group move to the object side, and at least the distance between the second lens group and the third lens group is variable at the same time.

Next, the means for ensuring the performance from the infinity to the finite distance in the lens system of the present invention will be described.

As described above, the lens system of the present invention has, in order from the object side, the first lens group G1 having a positive refractive power and the second lens group G2 having a positive refractive power sandwiching the aperture stop S and a negative lens group. It is composed of three basic lens groups of a third lens group G3 having a refractive power of
Reference numeral 1 denotes a doublet including at least one positive meniscus lens having a convex surface directed toward the object side, at least one set of meniscus lens and negative lens, and the second lens group G2 includes at least one set of negative lens and positive lens. Has a doublet and a positive lens, and the third lens group G3 has at least 1
When focusing from an object point at infinity to a finite object point, the first lens group G1, the second lens group G2, and the third lens group G3 are composed of a positive lens and a negative lens. It is characterized in that the lens group G3 is moved to the object side and the distance in each lens group is made variable at the same time in order to suppress variation in aberration.

Most conventional focusing methods in the modified Gauss type lens system are limited to the single-lens reflex type lens system.

On the other hand, in the lens system of the present invention, the back focus is short, and the third lens group is housed in the housing of the camera body. Therefore, there is no pioneering invention that even considers the drive mechanism.

In the present invention, as described above, the variation of aberration is corrected by changing the distance between the lens groups. For example, when focusing from an object point at infinity to an object point at a short distance of 0.5 m from the object point at infinity as in Example 1 [(A) and (B) of FIG. 2] described later, the second lens group G2 is moved to the group G2A, G2B
And the third lens group G3 is divided into groups G3A and G3B and moved separately to change the distance between the lens groups to compensate for aberration fluctuations.

Here, the means for correcting aberration variation during focusing according to the present invention will be described based on the aberration coefficient. Table 2 below shows each aberration coefficient when focusing on the object point of 0.5 m in Example 1 described above. Table 2 does not show the fifth-order aberration coefficients CM ₅ and AS ₅ of coma and astigmatism.

Table 2 SA ₃ SA ₅ CM ₃ AS ₃ DT ₃ PT ₃ G1 0.47814 0.23646 -0.26586 0.14264 0.58126 0.11484 G2 -0.56862 -0.20729 -0.67773 -0.47282 -1.13698 -0.41208 G3 0.04934 0.01514 0.94362 0.35256 0.61238 0.2218 Σ -0.44 0.02237 0.05666 -0.07545 As is clear from comparison between Table 2 and Table 1 showing the aberration coefficient at infinity in the same Example 1 described above, the coma aberration slightly fluctuates, but other aberrations are stable. You can see that That is, the second aspect which is the aberration fluctuation suppressing means of the present invention
It can be seen that the aberration variation during focusing is suppressed by the movement of the lens group sub-system and the movement of the third lens group sub-system.

In this embodiment, the second lens group is composed of a cemented doublet and a biconvex positive lens, and as the magnification becomes higher than infinity, the axial distance between both components becomes wider. preferable. Further, in the third lens group, it is desirable to move both components so that the axial distance between the positive lens on the object side and the negative lens on the image side becomes narrower as the magnification increases.

A method for controlling the image plane by changing the space in which the aperture stop is arranged is known. However, since a technique for maintaining a high interval precision is indispensable because the aperture device is inserted in this space, this space is required. Is more preferably not changed. Further, it is preferable to make the third lens group a fixed group in order to store this lens group in the housing. Therefore, if the optical performance can be maintained from the viewpoint of compensating for aberration variation, it is preferable to fix the third lens group.

Moving the cemented doublet and the positive lens in the second lens group in the lens system of the present invention by separating them is very effective for aberration correction.

In the lens system of the present invention equipped with the above-mentioned aberration variation correcting mechanism during focusing, it is desirable that the above-mentioned conditions (1) to (4) are satisfied.

[0038]

BEST MODE FOR CARRYING OUT THE INVENTION Next, embodiments of the present invention will be described based on examples.

The following data are Examples 1 to 4 of the standard lens of the present invention. Example 1 f = 54.999, F / 1.43, 2ω = 59.0 ° r ₁ = 45.7600 d ₁ = 5.4470 n ₁ = 1.80400 ν ₁ = 46.58 r ₂ = 121.9316 d ₂ = 0.1000 r ₃ = 29.3923 d ₃ = 5.7784 n ₂ = 1.74100 ν ₂ = 52.65 r ₄ = 58.6074 d ₄ = 1.3992 r ₅ = 129.0872 d ₅ = 2.7831 n ₃ = 1.68893 ν ₃ = 31.08 r ₆ = 20.7811 d ₆ = 7.0996 r ₇ = ∞ (diaphragm) d ₇ = 5.2572 r _{8 = -29.0337 d 8 = 2.0000 n 4} = 1.60323 ν 4 = 42.32 r 9 = -174.2021 d 9 = 4.2529 n 5 = 1.69680 ν 5 = 55.53 r 10 = -39.7244 d 10 = 0.1546 r 11 = 34.7750 d 11 = 7.5774 n _{6 = 1.49700 ν 6 = 81.61 r} 12 = -71.6423 d 12 = 5.5579 r 13 = 119.0206 d 13 = 11.6665 n 7 = 1.49700 ν 7 = 81.61 r 14 = -184.8317 d 14 = 12.9261 r 15 = -21.3238 d 15 = 2.0000 _{n 8 = 1.56883 ν 8 = 56.34} r 16 = -57.5286 ( object distance _{0.5m) d 10 = 2.412, d} 12 = 8.605, d 14 = 10.628 f 1 /f=4.362, f 1 / f 2 = 4.815, β ₃ = 0.95 58, f _b /f=0.128

Example 2 f = 55.0, F / 1.43, 2ω = 59.1 ° r ₁ = 47.5290 d ₁ = 5.5642 n ₁ = 1.80400 ν ₁ = 46.58 r ₂ = 166.0697 d ₂ = 0.1000 r ₃ = 29.1493 d ₃ = 5.5747 n ₂ = 1.78650 ν ₂ ＝ 50.00 r ₄ ＝ 54.6427 d ₄ ＝ 1.2922 r ₅ ＝ 100.0344 d ₅ ＝ 1.9000 n ₃ ＝ 1.68893 ν ₃ ＝ 31.08 r ₆ ＝ 19.9050 d ₆ ＝ 1.9000 n ₄ ＝ 1.78590 ν ₄ = 44.19 r _{7 = 19.7377 d 7 = 7.4732 r 8} = ∞ ( _{stop) d 8 = 4.2625 r 9 =} -38.0892 d 9 = 6.1567 n 5 = 1.70154 ν 5 = 41.24 r 10 = -17.2836 d 10 = 1.9000 n 6 = 1.74950 ν 6 = 35.27 r ₁₁ = -51.9093 d ₁₁ = 0.1000 r ₁₂ = 36.0019 d ₁₂ = 7.6754 n ₇ = 1.49700 ν ₇ = 81.61 r ₁₃ = -60.5726 d ₁₃ = 7.3838 r ₁₄ = 159.3934 d ₁₄ = 9.1431 n ₈ = 1.77250 ν ₈ = 49.60 r ₁₅ = -168.6921 d ₁₅ = 11.6742 r ₁₆ = -22.1595 d ₁₆ = 1.9000 n ₉ = 1.51602 ν ₉ = 56.80 r ₁₇ = -86.6002 (object distance 0.5 m) d ₁₁ = 1.727, d ₁₃ = 10.727, d ₁₅ = 9.691 f ₁ / f = 2.857, f ₁ / f ₂ = 2.823, β ₃ = 0.9194, f _b /f=0.128

Example 3 f = 55.0, F / 1.43, 2ω = 57.4 ° r ₁ = 49.4345 d ₁ = 5.2541 n ₁ = 1.80400 ν ₁ = 46.58 r ₂ = 144.4196 d ₂ = 0.1000 r ₃ = 29.9959 d ₃ = 6.0063 n ₂ = 1.74100 ν ₂ ＝ 52.65 r ₄ ＝ 65.0048 d ₄ ＝ 1.2966 r ₅ ＝ 140.2035 d ₅ ＝ 2.0000 n ₃ ＝ 1.74000 ν ₃ ＝ 31.71 r ₆ ＝ 21.2642 d ₆ ＝ 2.0000 n ₄ ＝ 1.74077 ν ₄ ＝ 27.79 r _{7 = 21.5858 d 7 = 6.7796 r 8} = ∞ ( _{stop) d 8 = 4.9813 r 9 =} -31.1827 d 9 = 2.0000 n 5 = 1.60717 ν 5 = 40.26 r 10 = 659.8383 d 10 = 4.8846 n 6 = 1.67000 ν 6 = 57.33 _{r 11 = -41.5361 d 11 = 0.5896} r 12 = 33.3443 d 12 = 7.3606 n 7 = 1.49700 ν 7 = 81.61 r 13 = -93.5696 d 13 = 7.7202 r 14 = 116.0042 d 14 = 6.8116 n 8 = 1.63854 ν 8 = 55.38 _{r 15 = -222.5918 d 15 = 14.2155} r 16 = -21.3304 d 16 = 2.0000 n 9 = 1.56965 ν 9 = 49.33 r 17 = -57.8521 ( object distance _{0.5m) d 11 = 2.857, d} 13 = 10.566, d ₁₅ = 12.367 f ₁ / f = 4.469, f ₁ / f ₂ = 4.809, β ₃ = 0.9198, f _b /f=0.128

Example 4 f = 54.999, F / 1.43, 2ω = 57.1 ° r ₁ = 44.6506 d ₁ = 5.7896 n ₁ = 1.78650 ν ₁ = 50.00 r ₂ = 140.5434 d ₂ = 0.1705 r ₃ = 28.9105 d ₃ = 5.4255 n ₂ = 1.72916 ν ₂ ＝ 54.68 r ₄ ＝ 51.5275 d ₄ ＝ 1.8949 r ₅ ＝ 111.5667 d ₅ ＝ 2.0000 n ₃ ＝ 1.68893 ν ₃ ＝ 31.08 r ₆ ＝ 20.9459 d ₆ ＝ 7.0373 r ₇ ＝ ∞ (Aperture) d ₇ ＝ _{5.0799 r 8 = -30.2712 d 8 =} 2.5730 n 4 = 1.60323 ν 4 = 42.32 r 9 = -290.1994 d 9 = 4.9666 n 5 = 1.71300 ν 5 = 53.84 r 10 = -42.2289 d 10 = 0.84527 r 11 = 33.6138 d 11 = 7.6346 n ₆ = 1.49700 ν ₆ ＝ 81.61 r ₁₂ ＝ -83.5858 d ₁₂ ＝ 9.7135 r ₁₃ ＝ 97.2164 d ₁₃ ＝ 7.3950 n ₇ ＝ 1.51633 ν ₇ ＝ 64.15 r ₁₄ ＝ -287.1247 d ₁₄ = 11.4744 r ₁₅ ＝ -21.7685 d _{15 = 2.0000 n 8 = 1.58267 ν} 8 = 46.33 r 16 = -62.2163 ( object distance _{0.5m) d 10 = 3.414, d} 12 = 12.731, d 14 = 9.238 f 1 /f=3.942, f 1 / f 2 = 4.405 , Β ₃ = 0.9725, f _b /f=0.128, where r ₁ , r ₂ , ... Are the radii of curvature of the respective lens surfaces, d
₁ , d ₂ , ... Is the thickness of each lens and the lens interval, n
₁ , n ₂ ,... Are the refractive indices of each lens, ν ₁ , ν ₂ ,.
Is the Abbe number of each lens. The unit of the length of the focal length f in the above data is mm.

Example 1 is a lens system shown in FIG.
Is an object point at infinity, and (B) is an object point distance of 0.5 m. In this embodiment, the focal length is 55 mm and the angle of view is 4
A so-called standard lens of 2.94 ° and an aperture ratio of 1: 1.
43.

In this lens system, an aperture stop is arranged between the first lens group G1 and the second lens group G2, and the third lens group G3 is composed of a biconvex positive lens and a negative meniscus lens. The first lens group includes a positive meniscus lens having a convex surface directed toward the object side in order from the object side, a positive meniscus lens having a convex surface directed toward the object side, and a negative meniscus lens having a strong concave surface directed toward the image side. The second lens group is a cemented doublet in which a negative meniscus lens having a strong concave surface facing the image side and a positive meniscus having a convex surface facing the object side are cemented, and a biconvex positive lens. It is composed of a lens.

The aberration situation of the first embodiment is as shown in FIG. 6, and in the standard lens for single-lens reflex, a relatively large negative distortion aberration occurs, but the distortion aberration is extremely small in this embodiment. . The chromatic aberration of magnification is also small in bending due to the occurrence of high-order aberrations.

Example 2 is the lens system shown in FIG. 3, in which the focal length is 55 mm, the angle of view is 42.94 °, and the aperture ratio is 1 :.
It is 1.43. The feature of the second embodiment is that a cemented lens of a negative meniscus lens and a positive meniscus lens is used as the third component of the first lens group, and the first component of the second lens group has a positive surface with a convex surface facing the image side. That is, a cemented lens of a meniscus lens and a negative meniscus lens is used.

The aberration situation of the second embodiment is as shown in FIG. 7, and the aberration tendency is the same as that of the first embodiment.

The third embodiment has a lens configuration as shown in FIG. 4, has a focal length of 55 mm, an angle of view of 42.94 °, and an aperture ratio of 1: 1.43. Example 3 is carried out in that the cemented lens as the first component of the second lens group is composed of a cemented lens of a negative lens having a strong concave surface facing the object side and a positive lens having a strong convex surface facing the image side. It differs from Example 2.

The aberrations of the third embodiment are as shown in FIG.

Example 4 is an example in which the astigmatic difference is further reduced by the variation of Example 1 in the lens system shown in FIG.

The aberration situation of the fourth embodiment is as shown in FIG. 9, and the astigmatism and the chromatic aberration of magnification are satisfactorily corrected.

In the drawings relating to each embodiment, (A),
(B) is an object at infinity and an object distance of 0.5 m.

In addition to the lens systems described in the claims, the lens systems described in the following items can also achieve the object of the present invention.

(1) A standard lens system characterized by satisfying the following conditions (1) to (4) in the lens system according to claim 2 of the claims. (1) 2.0 <f ₁ / f <10 (2) 1.0 <f ₁ / f ₂ <8 (3) 0.8 <β ₃ <1.3 (4) 0.1 <f _b / f <0.5

(2) In the lens system described in claim 2 or (1), the distance between the cemented doublet and the positive lens component constituting the second lens group is variable during focusing. A standard lens system.

(3) In the lens system according to claim 2 or claim (1), the distance between the positive lens component and the negative lens component constituting the third lens group is variable during focusing. Is a standard lens system.

(4) In the lens system described in claim 2 or (1), the distance between the cemented doublet and the positive lens component constituting the second lens group, and the third lens group. A standard lens system in which the distance between the positive lens component and the negative lens component constituting the lens is variable during focusing.

[0058]

According to the present invention, the first lens group having a positive refracting power, the second lens group having a positive refracting power and the third lens group having a negative refracting power sandwiching the aperture stop are arranged in order from the object side.
Considering the symmetry in the refractive power arrangement, which is composed of two basic lens groups, it is possible to easily perform sufficient correction of distortion aberration, sagittal coma aberration, or field curvature aberration, which were conventionally difficult. It has become possible. In addition, by using it as a general imaging optical system whose application range covers the entire visible range, it was possible to obtain sufficient optical performance by using a standard lens with a larger aperture than an open aperture. In addition, it has become possible to obtain high depiction performance and stability in a wide focusing range from an object point at infinity to an object point at finite distance.

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration of a lens system of the present invention and a state of a light beam.

FIG. 2 is a diagram showing a configuration of a first embodiment of the present invention.

FIG. 3 is a diagram showing a configuration of a second embodiment of the present invention.

FIG. 4 is a diagram showing a configuration of a third embodiment of the present invention.

FIG. 5 is a diagram showing a configuration of a fourth embodiment of the present invention.

FIG. 6 is an aberration curve diagram according to the first embodiment of the present invention.

FIG. 7 is an aberration curve diagram according to the second embodiment of the present invention.

FIG. 8 is an aberration curve diagram of Example 3 of the present invention.

FIG. 9 is an aberration curve diagram of Example 4 of the present invention.

Claims (2)

[Claims] 1. A first lens unit having a positive refracting power, a second lens unit having a positive refracting power, and a third lens unit having a negative refracting power sandwiching an aperture stop from the object side. The first lens group includes at least one positive meniscus lens having a convex surface directed toward the object side, at least one set of positive meniscus lens and doublet of negative lens,
The second lens group has at least one set of a doublet and a positive lens cemented with a negative lens and a positive lens, and the third lens group includes at least one positive lens and a negative lens.
A standard lens system which satisfies the following conditions (1), (2), (3), and (4) at the same time. (1) 2.0 <f ₁ / f <10 (2) 1.0 <f ₁ / f ₂ <8 (3) 0.8 <β ₃ <1.3 (4) 0.1 <f _b / f <0.5 where f ₁ is the focal length of the first lens group, f ₂ is the focal length of the second lens group, f is the focal length of the entire system, and β ₃ is the result of the third lens group at infinity. The image magnification, f _b, is the back focus of the entire system. 2. A first lens unit having a positive refracting power, a second lens unit having a positive refracting power, and a third lens unit having a negative refracting power sandwiching an aperture stop. ,
The first lens group includes at least one positive meniscus lens having a convex surface directed toward the object side, at least one set of meniscus lenses and a doublet of negative lenses, and the second lens group includes at least one set of negative lenses. It has a cemented doublet and a positive lens, and the third lens group has at least one
It is composed of a positive lens and a negative lens, and when focusing from an infinite object point to a finite object point, the first lens group, the second lens group, and the third lens group based on the infinite object point position. A standard lens system characterized in that the lens unit moves to the object side and at least the distance between the second lens unit and the third lens unit is variable at the same time.