JPH02146014A - Telephoto type objective - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention relates to a telephoto objective lens with a long focal length suitable for photographic cameras, video cameras, binoculars, etc. This invention relates to a high-performance telephoto objective lens with excellent aberration correction over the entire screen.

(Prior Art) Telephoto objective lenses with a long focal length have been widely used for photographing distant scenery, outdoor sports, and high-magnification binoculars.

A telephoto objective lens is constructed by arranging two lens groups, a front group having a positive refractive power and a rear group having a negative refractive power, spaced apart from each other in order from the object side.

Examples of these telephoto objective lenses include, for example, JP-A-61-
This method has been proposed in JP-A No. 188511, JP-A-62-112113, JP-A-63-106714, and the like. Generally, as the focal length of a telephoto objective lens becomes longer, the lens system becomes larger in proportion to the length, and the amount of political differences increases, making it difficult to obtain good optical performance. It's coming. For this reason, for example, telephoto objective lenses for photo cameras often consist of 3 to 5 lenses in the front group and 3 to 5 lenses in the rear group, and tend to be relatively large lens systems. there were.

(Problems to be Solved by the Invention) When trying to miniaturize the entire lens system by increasing the refractive power of the front and rear groups in a telephoto objective lens, many single-ring spherical aberrations, comatic aberrations, etc. occur. Also, there is a tendency for the curvature of field to become over-corrected.

Furthermore, the amount of chromatic aberration, especially secondary spectrum, increases,
There was a problem in that color bleeding was noticeable and it became very difficult to obtain good optical performance.

The present invention is a telephoto objective lens with a simple structure that has high optical performance while reducing the size of the entire lens system by appropriately setting the refractive power of the front and rear groups and the shape of each lens. The purpose is to provide.

(Means for solving the problem) It has two lens groups, a front group with a positive refractive power and a rear group with a negative refractive power, in order from the object side, and the front group has a positive first lens, a positive lens It has a second lens and a negative third lens, and the rear group has a positive fourth lens and a negative fifth lens, and the focal length of the entire system is f, and the focal length of the front group and the rear group is The distances are respectively fF and fR1
The air distance between the fourth lens and the fifth lens is D45. i-th
When the shape factor of the lens is S+, 0.55<fF/f<0.9
...(1) 0.8<1fR1/f<1.2.
fR<0...(2) Q, Ql<04. ,,
/f<0.06...(3)-3
<s4<-0,9...(4)0.8<35<3
...(5) is to be satisfied.

Note that the shape coefficient aS here is determined when the radii of curvature of the lens surfaces on the object side and the image plane side are respectively RA and RB.

(Example) FIGS. 1 to 3 are lens sectional views of numerical examples 1 to 3 of the present invention, respectively.

In the figure, the front group has a positive refractive power, and the rear group has a negative refractive power. In this embodiment, the front group and the rear group are separated by the largest air gap.

In this embodiment, as mentioned above, the front group with positive refractive power is composed of three lenses, the rear group with negative refractive power is composed of two lenses, and the front group and the rear group are composed of five lenses in total. By appropriately setting the refractive power of the lens and the lens shapes of the fourth and fifth lenses, we have created a telephoto objective lens that achieves good optical performance over the entire frame while reducing the size of the entire lens system. It has gained.

Next, the technical meaning of each of the above-mentioned conditional expressions will be explained.

Conditional expression (1) relates to the refractive power of the front group having positive refractive power, and is intended mainly to reduce the size of the entire lens system while correcting various political differences in a well-balanced manner.

If the upper limit is exceeded and the focal length of the front group becomes too long, that is, if the refractive power becomes too weak, the total length of the lens will increase, which is not good.If the lower limit is exceeded and the focal length becomes too short, μs refraction will occur. If the force becomes too strong, the entire lens system can be made smaller, but various political differences will occur, and in particular, zonal spherical aberration will increase, which is not good.

Conditional expression (2) relates to the refractive power of the rear group with negative refractive power, and is used together with conditional expression (1) to reduce the size of the entire lens system while compensating for various political differences, especially the curvature of field, in a well-balanced manner. be.

If the refractive power of the rear group becomes too weak beyond the limit value, the total length of the lens increases. If the lower limit is exceeded and the refractive power of the rear group becomes too strong, it is advantageous for downsizing the entire lens system, but it is not good because various aberrations, especially curvature of field, become overcorrected.

Conditional expression (3) is used to appropriately set the air distance between the fourth lens and the fifth lens, and mainly to correct astigmatism, coma aberration, curvature aberration, etc. in a well-balanced manner. If the air spacing becomes too wide beyond the upper limit, astigmatism, coma, and curvature aberration will be overcorrected, and if the air spacing becomes too narrow beyond the lower limit, astigmatism and coma will be undercorrected. , it becomes difficult to satisfactorily correct these various aberrations.

Conditional expression (4) relates to the lens shape of the positive fourth lens, and is intended to satisfactorily correct annular spherical aberration and coma aberration.

If the upper limit is exceeded, both lens surfaces become convex, and the refractive power of the object-side lens surface becomes stronger, resulting in insufficient correction of coma aberration. Furthermore, if the lower limit is exceeded and the degree of meniscus with the convex surface facing the object side becomes strong, coma aberration is well corrected, but annular spherical aberration increases, which is not good.

Conditional expression (5) relates to the lens shape of the negative fifth lens, and is mainly intended to satisfactorily correct one-zone spherical aberration and astigmatism.

If the lower limit is exceeded and the meniscus degree becomes stronger, with the concave surface facing the object side, the annular spherical aberration will increase, and if the lower limit is exceeded, both lens surfaces will become concave, and the refractive power of the lens surface on the image side will become stronger. If this happens, astigmatism will be over-corrected and curvature aberration will also be over-corrected, which is not good.

The telephoto objective lens according to the present invention is achieved by satisfying the above conditions, but in order to satisfactorily correct the chromatic aberration, especially the secondary spectrum, which occurs when the focal length is made longer, the following conditions must be met. It is better to satisfy the conditions.

The focal length of the second lens is f2. The partial dispersion ratio of the material of the second lens is 02. When g, F, and Atsube number are ν2, 0.025 < 02. gy −(0, fi438-0
．． 00168 @ ν )<o, oe... (6) 80<ν2...(7) 0.3<
f2/f<0.55... (8)
0.2<S2<0.7...
(9) The following condition must be satisfied.

Here, the partial dispersion ratio θ1. F is Fraunhofer line g
The refractive powers for the line, F line, and C line are Ng and NF, respectively.

N(, when This is the value found by

Conditional expressions (6) and (7) are intended to mainly correct the secondary spectrum favorably by using an anomalous dispersion glass material as the material of the positive second lens.

Conditional expression (6) expresses Atsube number ν2 and partial dispersion ratio θ2 as
It is representative of ordinary glass materials on the graph taken along the axis. Taking 7 and the product name F2 as the product name, the temperature number ν of these two glass materials is
, and the partial dispersion ratio ON is a straight line 0N=O-643,8
It represents the deviation from 0-00168@νN.

The larger this value, the greater the anomalous dispersion.

In January, when no light was emitted, an optical glass material with anomalous dispersion and low dispersion that satisfied conditional expressions (6) and (7) was used, while satisfying conditions (8) and (9), which will be described later. This effectively corrects the secondary spectrum as well as aberrations and coma.

Conditional expression (8) relates to the refractive power of the second lens, and conditional expression (9)
) relates to the lens shape of the second lens, and conditional expression (6), (
7) and is mainly used to properly correct the secondary spectrum.

If the upper limit of conditional expression (8) is exceeded and the refractive power of the second lens becomes weak, the correction effect of the secondary spectrum will be reduced, and if the lower limit is exceeded and the refractive power of the second lens becomes strong, the annular spherical aberration will be reduced. It's not good because it happens a lot.

If the upper limit of conditional expression (9) is exceeded and the refractive power of the lens surface on the object side of the biconvex lens surfaces becomes stronger, the annular spherical aberration increases, and if the lower limit is exceeded, the refractive power of the lens surface on the image side increases. If it becomes strong, coma aberration will occur more towards the periphery of the screen, which is not good.

In numerical example 1 shown in FIG. 1, the front group I is composed of three lenses: a first lens whose both lens surfaces are convex, a second lens whose both lens surfaces are convex, and a third lens whose both lens surfaces are concave. The rear group (2) is composed of two lenses: a meniscus-shaped fourth lens with a convex surface facing the image plane and a fifth lens with a concave surface facing the object side.

Numerical Example 2.3 shown in FIGS. 2 and 3 is applied to an objective lens for high-magnification binoculars, and the number f in FIG.
Except for the fact that the second lens and the third lens on the main layer side 3 are cemented together, the lens formation is the same as in the numerical embodiment shown in FIG. 1.

Note that P placed behind the lens is a prism for observing an erect image used in binoculars, and is shown as an expanded glass block in the figure.

Generally, in high-magnification binoculars, the total lens length of the objective lens increases, but according to the present invention, the entire lens system can be made smaller, while providing high optical performance that satisfactorily corrects various political differences including secondary spectra. The objective lens of the source is easily V).

In Numerical Example 3 shown in FIG. 3, the refractive power of the second lens is strengthened within the range of conditional expression (8) compared to Numerical Example 2, and the second-order lens is The spectrum is well corrected.

In each of the above embodiments, focusing is performed by moving the entire lens system or by moving part or all of the rear group.

Next, several fth embodiments of the present invention will be shown. In numerical embodiments, Ri is the curvature of the first lens surface -#'? in order from the object side.
! ! ' diameter, Di is the first lens thickness and air distance from the object side, Ni and νi are Q'lr in order from the object side, respectively.
This is the 7+ii refractive index of the glass of the i-th lens and the %.

Furthermore, Table 1 shows the relationship between each of the above-mentioned conditional expressions and the word values in the numerical examples.

Numerical Example 1 F=100 FNo=1: 5 R1-38,7501-2,75 R2--190,1502-0,30 R3-28,3703~3.0O R4--78,0004-0,06 R5-73, HD5-1, 50 R6-34, 1906-32, 98 R7--83.18 07-1.50 R8 demand-21,
4306-2,84 R9 Leaf-15,57D9 False 0.87 RIO Tomi 27G, 85 2ω= 2.06 @ 1.58013 ν l 70.2 ν 2-95.1 ν 3-48.4 ν 4-35.3 ν 5 snow 47.0 Numerical Example 2 F=100FNo-1:52ω-1,25°× 2RI=
28.15 01=2.88 N1=
Bow, 4B749 ν 1-70.2R2--199
,8802±0.30 R3-30,0003-2,88N2-1.43387
ν2 straw 95. lR4--87,5104-0,10 R5=-81,8205-1,50N3-1.823
74y3=47. IR8-32, 78n8=22
．． 63 R7 earthquake-54,0307=1.50 84=1. ? 4
950 Shi4-35.3R8--20,3306-2
,83 R9=-15,4509-0,88N5=1.582
87 Shi5-46.4RIG--178.06 [
110-13,50 Numerical Example 3 F=100 FNo-1: 5 2ω-1,
25” Xl-30, 3801-2, 83Ml-1,
487492 薯350, 2902-0, 30 3-25, 5403-3, 8882-1, 433874
--38,77D 4 proverbs 1.50 N3-1.521
305- 23.89 05-22.20 8 謔 -55,37D 8 wealth 1.50 84ヰ1.749507--18.14 07-1.94 8= -14,8306-0,88N5-1.5673
23-34L37 [) 9 pieces 13.50!470.
2 ν 2 Tatsumi 95.1 ν 3 volume 52.5 ν 4 volume 35.3 ν 5-42.8 (Table-1) (Effect of start 1) According to the present invention, as described above, the front group and the rear group By appropriately setting the refractive power of the lens and the shape of each lens, it is possible to create a high-performance, compact telephoto model that effectively corrects aberrations over the entire screen despite its simple configuration of only five lenses. objective lens can be achieved. In addition, by using an anomalous dispersion glass material such as fluorite as the material of the second lens under certain conditions, it is possible to achieve high optical performance with good correction of the secondary spectrum while maintaining good annular spherical aberration and carp aberration. A high performance telephoto objective lens has been achieved.

[Brief explanation of the drawing]

1 to 3 are lens sectional views of numerical examples 1 to 3 of the present invention, and FIGS. 4 to 6 are various aberration diagrams of numerical examples 1 to 3 of the present invention. In the figure, 1 is the front group with positive refractive power, ■ is the rear group with negative refractive power, P
is an expanded block diagram of Seitatekawa's prism, d is the d-line,
C is the C line, g is the d line, S is the sagittal image plane, and 1M is the meridional image plane. Figure Figure Figure ω: 2.06” ω 2,06° ω = 2.06° - u, +u 0010 Aqua regia ih fits E -CLIOo, t. 11th floor, q and left -2,00200 Distortion jl:i (%J 0.01 0.01 times Kimuraq scale difference ω; t25°ω=1.25°ω=1.25°−2,002,00 Distortion M to the left (%) − 0,010,01 Double Ki-mura - Matazazu Sei 9L-row Igyu J = 1.25' ω = 1.25'

Claims (1)

[Claims] (1) It has two lens groups, a front group with a positive refractive power and a rear group with a negative refractive power, in order from the object side, and the front group includes a positive first lens and a positive second lens. The rear group has a positive fourth lens and a negative fifth lens, and the focal length of the entire system is f, and the focal length of the front group and the rear group is each f_F
, f_R, the air distance between the fourth lens and the fifth lens is D
_4_, _5, when the shape factor of the i-th lens is Si, 0.55<[f_F]/f<0.3 0.8<[|f_R|]/f<1.2, [f_R]<0
0.01<[D_4_,_5]/f<0.06-3<[
A telephoto objective lens that satisfies the following conditions: S_4]<-0.9 0.8<[S_5]<3. (2) When the focal length of the second lens is f_2, the partial dispersion ratio of the material of the second lens is θ_2_, _g_, _F, and the Abbe number is ν_2, 0.025<θ_2_, _g_, F-(0. 6438-
0.00168·ν_2)<0.0680<ν_2 0.3<[f_2]/f<0.55 -0.2<S_2<0.7 Telephoto objective lens.