JPS60122917A - High performance variable power read lens system - Google Patents

Abstract

PURPOSE:To realize a lens which has a variable power ratio of twice or more, also is compact, and has high performance in all magnifications by constituting a lens system of a front group and a rear group, and also satisfying a specified condition. CONSTITUTION:A variable power read lens system is constituted of a front group having a negative focal distance, and a rear group having a positive focal distance, from an object side, and in case when a variable power is executed to a magnification from a low magnification, it is executed by reducing an interval of the front and the rear groups, enlarging a focal distance, and also reducing a distance between an object and an image. Also, an expression I and an expression II are satisfied, when fmin, fmax, K, and f1 denote a focal distance of the whole system of a low magnification side, a focal distance of the whole system of a high magnification side, a variable power ratio of a use magnification, and a focal distance of the front group, respectively. In this way, a variable power read lens system which has a large variable power of two times or more, also is compact, and has a high performance in all magnifications can be obtained.

Description

[Detailed description of the invention]

The present invention is a high-performance variable magnification reading lens system having a magnification range (on the reduction side) of about 177 to 1/20 times (if the object and image plane are reversed, it can also be used as an enlargement photographing lens system for enlarging, etc.). )
The objective is to provide a lens system that has a variable magnification ratio of 2x or more, is compact, and has high performance at all magnifications. Conventionally, as for variable magnification lenses, a so-called zoom lens with a constant distance between objects and images has been used to change the magnification.
No. 715 exists, but its variable magnification ratio is as small as about 1.6 times, and the size of the lens system is several times larger than a fixed focal length lens system. There are also many fixed focal length lens systems known, but they can only be said to have high performance at a certain magnification, and only at a magnification very close to that. The present invention has an intermediate configuration between a zoom lens and a fixed focal length lens, and magnification is mainly performed by changing the object-to-image distance in the same way as a fixed focal length lens, but by changing a part of the distance within the lens system. This allows us to achieve high performance over the entire range of magnifications used, with a variable power ratio of 2x or more. In addition, when changing the distance between some parts of the lens system, the object is fixed by increasing the focal length on the high magnification side, so as a means of changing the object-image distance, a mirror is placed in the middle and the position of the mirror is changed. A method in which the mirror is moved is generally known, but it is effective in reducing the amount of movement of this mirror, and is very advantageous in terms of compactness of the device. First, to explain the present invention in detail, from the object side, it is composed of a front group with a negative focal length and a rear group with a positive focal length, and when changing from low magnification to high magnification, the distance between the front and rear groups is changed. (i) υ, l (υ, 1 1f1). f min : Entire system on the low magnification side focal length f max
: Focal length K of the entire system on the high magnification side : Variable magnification ratio fl of the magnification used : This is a high performance variable magnification reading lens system that satisfies various conditions for the focal length of the front group. In addition, in the above lens system, the front group consists of a negative meniscus lens and a positive meniscus lens with a convex surface facing the object side from the object side, where fl: focal length of the negative meniscus lens d2: negative meniscus lens and positive meniscus lens. Air distance r3 between lenses: configured to satisfy the condition of the object-side radius of curvature of a positive meniscus lens. The rear group is similar to the conventional type of fixed focal length lens system. In the present invention, the rear group employs a Gauss type or a modified orthometer type with eight elements in six groups. Furthermore, the front group is fixed with respect to the image plane during zooming. This is desirable because it simplifies the structure of the mirror frame. Next, each of the above conditions will be explained. Condition (1) relates to the ratio of the increment in the change ratio of the focal length to the ratio of the zoom ratio, and if the lower limit is exceeded. On the high magnification side, the focal length becomes smaller and the amount of change in the object-to-image distance becomes larger, which goes against the desire to make the reading device more compact as described above. Furthermore, if the upper limit is exceeded, the amount of change in the object-to-image distance becomes smaller, which has the advantage of approaching a zoom lens system, but it becomes difficult to maintain high performance over the entire magnification range of 2x or more. Therefore, the lens system itself becomes large. Condition (2) relates to the power of the front group; if the lower limit is exceeded, it is advantageous in terms of aberration correction, but the amount of change in the focal length of the entire system with respect to the change in the distance between the front and rear groups becomes small, resulting in an increase in the size of the lens system. If the upper limit is exceeded, the power of the front and rear groups will become stronger, which is advantageous for the compactness of the lens system, but it will not be possible to maintain high performance at all magnifications used above 2x. In a reading device, the entire image plane must have high performance at all magnifications, so the power of the front group is quite small compared to a general zoom lens for photography. Conditions (3) to (5) relate to the power arrangement in the front group, and if the lower limit of condition (3) is exceeded, aberration correction of 1 is advantageous, but d2 increases and the size increases. If the upper limit is exceeded, the radius of curvature r2 of the second surface of the negative meniscus lens becomes smaller, and the radius of curvature r3 of the positive meniscus lens also becomes smaller accordingly, resulting in an increase in changes in spherical aberration and comatic aberration during zooming. invite. Condition (4) is also related to condition (3), but when the lower limit is exceeded, the power of both the negative and positive meniscus lenses in the front group becomes strong, and the upper limit of condition (1) is 9. It violates the lower limit and is not appropriate. Also, if the upper limit is exceeded,
Although this is advantageous in correcting aberrations, the lens system becomes large and is not suitable. As stated in condition (3), condition (5) means that if the lower limit is exceeded, changes in spherical aberration and comatic aberration will increase during zooming, and if the upper limit is exceeded, r2 must also be increased. As a result, the power of the negative meniscus lens becomes smaller, leading to an increase in d2 and a larger size. Examples 1 and 2 of the present invention are shown below. Here, r is the radius of curvature, d is the lens thickness or air gap, N is the refractive index of d-1ine, ν is the Atsube number, F is the aperture ratio to the ω object, f
is the focal length of the entire system, y is the image height half angle of view, 1 m is the lateral magnification, U is the object-to-image distance, and fB is the back focus.

[Example 1] F=4.5 f=30.0-31.4 7=14.5m
= -0,055~-0,1323U = 610~
305.5f B =22.8~25.8 No, r d N 1 61.227 1.70 1.69680 55.
52 21.281 2.40 3 24.066 2.50 1.71736 29.
54 31.657 5.00~2.005 22.0
26 3.40 1.80610 40.96 99.
686 0.10 7 11.894 1+, 10 1.78590 44
．． 28 56.616 1.20 1.8051B 2
5.49 8.051 2.24 10 14.256 1.30 1.58913 61
．． 011 17.326 2.00 12 -14.804 1.30 1.58913 6
1.013 -22.388 1.40 14 -9.146 1.20 1.76182 26
．． 615 -30.066 3.40 1.78590
44.216 -12.379 0.10 17 -57.869 2.60 1.80610 4
0.918 -23.518 1f l l

[Example 2] F=4.5 f=35.2 to 37.2 y=14.5m
= -0,055--0,13230=716.7
-361.4f B =28.2~32. O NO・ r d N Ya1 69.962 1.80 1.69680 55.
52 20.726 3.51 3 21.989 3.00 1.71736 29.
54 31.285 5.2-1.4 5 27.634 3.70 1.80610 40.
96 240.514 0.10 7 14.801 5.00 1.78590 44.
28 -195.550 1.30 1.80518
25.49 10.709 4.18 10 34.132 1.40 1.58913 61
．． 011 43.446 2.31 12 -36.242 1.40 1.58913 6
1.013 -19.142 1.50 14 -8.878 1.30 1.76182 26
．． 615 -21.700 3.10 1.78590
44.216 -12.638 0.10 17 -48.446 2.40 1.80610 4
0.918 -22.257 11! 1

[Brief explanation of drawings]

1st. FIG. 3 is a lens system configuration diagram on the low magnification side corresponding to Example 1.2. Figure 2 (a), (b), (c), Figure 4 (a)
, (b) and (c) are various aberration diagrams corresponding to Examples 1 and 2, respectively, where (a) shows the aberration diagram on the low magnification side, (b) shows the aberration diagram on the intermediate magnification side, and (C) shows the aberration diagram on the high magnification side. . Figure 1 Figure 2 Sine condition Figure 2 vN2 Figure 4 Sine condition Figure 4 Figure 4 Sine condition Figure 4 Figure 4 Et situation

Claims (1)

[Claims] l From the object side, a front group having a negative focal length. It consists of a rear group with a positive focal length, and when changing from low magnification to high magnification, the distance between the front and rear groups is decreased, the focal length is increased, and the object-image distance is decreased. However, and. f ll1in: Focal length of the entire system on the low magnification side f wa
x: Focal length of the entire system on the high magnification side K: Variable magnification ratio f of the magnification used! : High performance variable magnification reading lens system that satisfies the focal length conditions of the front group. 2 The front group consists of a negative meniscus lens with a convex surface facing the object side and a positive meniscus lens from the object side. However, f! =Focal length d2 of the negative meniscus lens: Air distance r3 between the negative meniscus lens and the positive meniscus lens: High performance variable magnification according to claim 1, which satisfies the condition of the object-side radius of curvature of the positive meniscus lens. Reading lens system. 3. A high-performance variable magnification reading lens system according to claim 1, wherein the front group is fixed when the image plane is taken as a reference during variable magnification.