JPH0442651B2 - - Google Patents

Description

[Detailed description of the invention]

a. Technical Field The present invention relates to a zoom lens for a 35 mm still camera, which covers everything from wide-angle to telephoto, and has a zoom ratio of about 6x, which is extremely high for a 35 mm still camera. b. Conventional technology and its problems Conventional zoom lenses for 35mm still cameras are
It used to be common for zoom ratios to be 2 to 3 times, but in recent years there has been an increasing demand for even higher zoom ratios, and zoom ratios of 5 to 3 times have increased.
Zoom lenses with extremely high specs for 6x 35mm still cameras have appeared. As a wide-angle zoom lens with a high zoom ratio,
The conventional methods are listed below. The variable magnification ratio is 2 to 3 times, and the half angle of view on the long focus side is approximately
About 15 degrees. The zoom ratio of this class, the front group is negative when zoomed out,
There are known two-group types with a positive rear group, or four-group variations of the two-group type in which the positive rear group is further divided into three groups: positive, negative, and positive.
In any case, it is basically a retrofocus type, and if you try to obtain a high zoom ratio of 3x or more, or make the telephoto side even longer focal length, it will inevitably lead to an increase in the rear lens system. Therefore, it is inappropriate. The variable magnification ratio is 3 to 5 times, and the half angle of view on the long focal point side is approximately 9 degrees.
Something of a degree. In this class, there is no negative first lens group as described in , but there are three groups: positive, negative, positive, or four groups: positive, negative, positive, positive, or positive, negative, positive.
A zoom type that consists of five lens groups, negative, positive, negative, and positive, in which almost all lens groups are movable (there are also models in which the second, third, or fifth lens group is fixed) has become known. However, the variable magnification ratio is up to 5x and the half-angle of view on the long focal length side is about 9 degrees, which is not enough as a telephoto lens. The variable magnification ratio exceeds 5x, and the half angle of view on the long focal length side is approximately 6°. There are still few products of this class, and the known ones are Example 1 of JP-A No. 57-161804, Example 2 of JP-A No. 57-161824, Examples 1 to 4 of JP-A No. 58-127908, and There is JP-A-60-14213,
The second lens group is composed of five elements in three groups or five elements in four groups, and perhaps because the load on the second lens group is large, the fluctuations in comatic aberration and specific point aberration are large during zooming. c Purpose The present invention is a 35mm still camera lens that covers everything from wide-angle to telephoto, and has a very large variable magnification ratio of about 6x, which corresponds to the commonly used lens range, that is, a half-angle of view of about 32x on the short focal length side. degree (equivalent to a focal length of 35 mm) and a half-angle of view of about 6 degrees (equivalent to a focal length of about 200 mm) on the long focal length side, all in one compact, high-performance zoom lens. The purpose is to obtain a variable power ratio zoom lens. d Structure of the Invention The present invention includes, in order from the object side, a first lens group having a positive focal length and a second lens group having a negative focal length.
It consists of a lens group, a third lens group with a positive focal length, and a fourth lens group with a positive focal length, and all of the first, second, third, and fourth lens groups can be moved. Therefore, change the focal length,
In a zoom lens in which the image plane position is constant, the first lens group consists of a negative meniscus lens with a convex surface facing the object side and two positive lenses, and the second lens group includes: From the object side, a negative lens with a concave curvature on the image side, a biconcave negative lens with a large curvature on the mating surface and a positive lens, and a concave curvature on the object side. It consists of four large negative lenses in three groups, and the third lens group consists of two positive lenses and a negative lens with a concave surface with a large curvature facing the object side, from the object side. The fourth lens group includes, from the object side, one or two positive lenses having a convex object side surface and at least one
a front group consisting of a negative lens and a positive focal length, a middle group of a negative lens and a positive lens whose bonding surface has a diverging surface with a large curvature convex to the object side, and a positive lens. It consists of a rear group consisting of a negative meniscus lens having a concave surface with a large curvature on the object side, and (1) 0.0＜X〓 _L /X〓 _L <0.4 (2) 1.7＜〓 _o ( 3) 0.08＜r〓 _c ／f _L ＜0.15 (4) 0.09＜r〓 _1a ／f _L ＜0.18 (5) 0.07＜r〓 _c ／f _L ＜0.14 (6) −0.12＜r〓 _Ea ／f _L <-0.06 _However , X〓 _L : Amount _of movement on the long focal point side of the first lens group Average value of refractive index f _L : Focal length of the entire system on the long focal length side r〓 _c : Radius of curvature of the joint surfaces of the joint lenses in the second lens group r〓 _1a : At the most object side of the fourth lens group Radius of curvature of the object side of a certain positive lens r〓 _c : Middle group of the 4th lens group (glued lens)
Radius of curvature of the mating surface r〓 _Ea : A high zoom ratio zoom lens that covers a wide angle range and is characterized by satisfying the conditions for the radius of curvature of the object side of the negative lens closest to the image side of the fourth lens group. It is. Furthermore, in the zoom lens having the above characteristics, the present invention provides that when the first, third, and fourth lens groups move from the short focus side to the long focus side, they move monotonically toward the object side, and the third, third, and fourth lens groups move monotonically toward the object side; When the amount of movement on _{the long} focal point side of the fourth lens group is respectively X〓 _and Amount of movement X〓 _L : Characterized by satisfying the condition for the amount of movement of the fourth lens group on the superfocal side. Furthermore, the present invention is characterized in that the first lens group and the fourth lens group move together to perform zooming in the zoom lens having the above-mentioned characteristics. e Functions and Effects of the Invention The present invention is of a type in which all four lens groups move, but the first lens group has two roles: focusing and assisting the variable power effect of the second lens group. The second lens group and the fourth lens group have substantially the same magnification changing function. Further, the third lens group has a function of properly correcting the flatness of an image when changing the magnification in relation to the fourth lens group, rather than having a variable magnification function. In conventional lenses, when changing from the short focal length side to the long focal length side, the second lens group moved toward the image side in most cases, placing a very large burden on the second lens group. When changing from the short focal length side to the long focal length side, the second lens group of It is characterized by being located closer to the object on the focus side than on the short focus side. Conditions (1), (2), and (3) relate to the second lens group. Condition (1) is related to the movement of the second lens group,
If the lower limit of this condition (1) is exceeded, the second lens group will be located closer to the image side on the long focal length side than on the short focal length side, increasing the burden on the second lens group for zooming, and the fourth lens The balance of the variable power function with the lens group is lost, leading to an increase in changes in coma aberration and astigmatism during zooming, and the configuration of four elements in three groups cannot correct these aberrations. If the upper limit is exceeded, the amount of movement of the first lens group and the fourth lens group will increase, which not only goes against the need for compactness, but conversely, the burden of changing the magnification of the fourth lens group will not be too large, and it will be difficult to use high-order lenses. It becomes difficult to correct spherical aberration and curvature of field. Condition (2) concerns the average refractive index of the negative lens in the second lens group, and if the lower limit of this condition (2) is exceeded, the Petzval sum tends to become negative, especially the sagittal value at the maximum angle of view on the short focus side. The directional astigmatism tends to become positive, which is not preferable. Condition (3) relates to the bonding surface of the bonding lens in the second lens group, that is, the converging surface of the second lens group, which is a diverging lens group. This surface is not glued together, but some lenses are separated into a negative lens and a positive lens. It's better to If the upper limit of this condition (3) is exceeded, the effect as a convergence surface becomes smaller,
Various aberrations that diverge in the second lens group become too large, making it difficult to correct the aberrations in the third and fourth lens groups. If the lower limit is exceeded, high-order aberrations occur, and the change in the periphery of the spherical aberration on the long focal point side in particular becomes abrupt, which is not preferable. Conditions (4), (5), and (6) relate to the fourth lens group. Condition (4) concerns the power of the object side of the positive lens closest to the object in the fourth lens group, and when the upper limit of condition (4) is exceeded, the positive surface power decreases and the negative power decreases. It becomes difficult to correct excessive aberrations that occur in the large second lens group. If the lower limit is exceeded, the surface power becomes too large, and the change in spherical aberration at the periphery, especially on the long focal point side, becomes abrupt, which is not preferable. Condition (5) relates to the bonding surface of the middle group in the fourth lens group, and the middle group as a whole has both cases of positive power and negative power. However, a diverging surface is required.
If the upper limit of this condition (5) is exceeded, the diverging surface effect becomes small, making it impossible to correct the under-aberrations that occur in the fourth lens group, which has a large positive power.On the other hand, if the lower limit is exceeded, the power of the diverging surface becomes If it becomes too large, high-order spherical aberration is likely to occur, and fluctuations in spherical aberration and comatic aberration with respect to zooming also increase, which is undesirable. Condition (6) relates to the power of the object side of the final negative lens in the fourth lens group, which is a diverging surface like condition (5). However, the effect differs from condition (5) depending on the position of the lens. That is, condition (6)
In the case of , it is effective in correcting field curvature and distortion aberration because it relates to a lens that is further away than the aperture position. If the lower limit of this condition (6) is exceeded, the power of the diverging surface becomes small, making it impossible to correct the negative (barrel-shaped) distortion that occurs in the front group of the third and fourth lens groups. The distortion aberration on the focus side becomes a large negative value. If the upper limit is exceeded, the power of the diverging surface increases, which is advantageous for correcting distortion on the short focus side, but the Petzval tends to become negative and the field curvature tends to become excessive. Moreover, arranging a negative lens as the final lens is advantageous for downsizing since the fourth lens group becomes a telephoto type. Condition (7) relates to the movement of the third and fourth lens groups; as mentioned above, the third lens group is not related to the variable power function, but moves relative to the fourth lens group during variable power. This is to properly correct the flatness of the image. If the upper limit of this condition (7) is exceeded,
The third lens group approaches the amount of movement of the fourth lens group,
Since the change in distance between the third and fourth lens groups becomes small, astigmatism becomes excessive on the long focal point side, which is not preferable. If the lower limit is exceeded, the change in the distance between the third and fourth lens groups will increase, which is advantageous for correcting astigmatism, but the amount of movement of the fourth lens group will increase,
To set the F number to around 4.5 on the long focus side,
This increases the diameter of the rear ball and goes against compact design. Further, an increase in the rear ball diameter is not preferable because it also leads to an increase in flare. f Examples Examples 1 to 4 of the present invention will be described below. Where, f is the focal length, Z is the zoom ratio, ω is the half angle of view, f _B is the back focus, r is the radius of curvature of each lens surface, d is the lens thickness or distance between lenses, and N is the d-line of each lens. The refractive index of and ν indicate the Abbe number of each lens.

【table】

【table】

【table】

【table】

【table】

【table】

【table】

【table】 [Brief explanation of drawings]

1, 3, 5, and 7 are configuration diagrams of lens systems on the short focus side corresponding to Examples 1, 2, 3, and 4 of the present invention, respectively. Figures 2, 4, 6, and 8 are aberration diagrams of Examples 1, 2, 3, and 4, respectively, where a shows the state at the short focus side, b shows the intermediate focal length, and c shows the state at the long focus side. show.

Claims (1)

[Claims] 1. In order from the object side, a first lens having a positive focal length;
Consisting of a lens group, a second lens group having a negative focal length, a third lens group having a positive focal length, and a fourth lens group having a positive focal length,
In a zoom lens in which the focal length is changed by moving all of the first, second, third, and fourth lens groups, and the image plane position is constant, the second lens group, from the object side, A negative lens with a concave image side and a large curvature, a composite lens with a positive lens and a double-concave negative lens whose mating surface is convex toward the object side and a large curvature, and a negative lens with a concave object side and a large curvature on the object side. The fourth lens group includes, from the object side, one or two positive lenses each having a convex object side surface and at least one positive lens.
a front group consisting of a negative lens and a positive focal length, a middle group of a negative lens and a positive lens whose bonding surface has a diverging surface with a large curvature convex to the object side, and a positive lens. It consists of a rear group consisting of a negative meniscus lens having a concave surface with a large curvature on the object side, and (1) 0.0＜X〓 _L /X〓 _L <0.4 (2) 1.7＜〓 _o ( 3) 0.08＜r〓 _c ／f _L ＜0.15 (4) 0.09＜r〓 _1a ／f _L ＜0.18 (5) 0.07＜r〓 _c ／f _L ＜0.14 (6) −0.12＜r〓 _Ea ／f _L <-0.06 _However , X〓 _L : Amount _of movement on the long focal point side of the first lens group Average value of refractive index f _L : Focal length of the entire system on the long focal length side r〓 _c : Radius of curvature of the joint surfaces of the joint lenses in the second lens group r〓 _1a : The closest to the object side of the fourth lens group Radius of curvature of the object side of a certain positive lens r〓 _c : Middle group of the 4th lens group (glued lens)
Radius of curvature of the mating surface r〓 _Ea : A high zoom ratio zoom lens that covers a wide angle and is characterized by satisfying various conditions for the radius of curvature of the object side of the negative lens closest to the image side of the fourth lens group. . 2. When the first, third, and fourth lens groups move from the short focus side to the long focus side, they move monotonically toward the object side, (7) 0.5<X〓 _L /X〓 _L A high zoom ratio zoom lens encompassing a wide angle according to claim 1, which satisfies the condition of <0.9. However, X〓 _L : Amount _of movement on the long focal point side of the third lens group A high zoom ratio zoom lens covering a wide angle as claimed in claim 1.