JPS58179808A - Retrofocus lens consisting of five lenses of five groups - Google Patents

Abstract

PURPOSE:To obtain a bright and wide-angle object lens without curvature of field and distorted aberration, by satisfying prescribed various conditions in five lenses of five groups. CONSTITUTION:A concave meniscus lens whose convex directed to the object side and a double convex lens whose face having a shorter radius of curvature is directed to the object side are provided as the first group and the second group respectively in order from the object side. A double concave lens whose face having a shorter radius of curvature is directed to the object side is provided as the third group, and convex meniscus lenses whose faces having a shorter radius of curvature are directed to the image side are provided as the fourth group and the fifth group, and thus, this retrofocus lens consists of five lenses of five groups. In these lens groups, various conditions of inequalities I -VII are satisfied. In figure and inequalities, r1, r2-r10 are radiuses of curvature of faces in order from the object side, and d1, d2-d9 are intervals of faces in order from the object side, and n1, n2-n5 are refractive indexes of respective lenses, and nu1, nu2-nu5 are Abbe's numbers of respective lenses, and f1 is the focal length of the first lens, and f1.2.3 is the resultant focal length of the first - the third lenses.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a retrofocus type wide-angle objective lens having a WR- lens configuration and being bright.

A retrofocus lens consists of 111 elements in 5 groups, with a concave lens followed by a convex, concave, convex, and convex lens, and has a small number of elements and has good performance up to a half angle of view of around 30.
rt lens type, and there are many known examples.

For example, Japanese Patent Publication No. 46-24194 was the first patent for a retrofocus lens with five elements in five groups.
As the amount of light increases, the lateral aberration of incident light with a high incident height increases, resulting in flare.

The cause of this is the ratio of the non-point distance of the entire system @f and the composite focal length from the first lens to the third lens f1.1&/ft2. This is because 5 is a large negative sister-in-law, and the chromatic aberration of magnification is also large.

In the lens described in JP-A-51-56625, the fifth group is a positive lens with a strongly convex surface facing the object side, but with this shape, the field curvature and distortion are negative and create a large gap. To correct this, the radius of curvature r5 of the image side surface of the second lens is made small, but the seven-digital removal surface that makes the radius of curvature of this surface small causes the astigmatism to become positive in excess of If. Getting worse.

In the present invention, the absolute value of '/fttx is made smaller than that of the conventional lens, and the refractive index of the convex lens is set high in order to prevent an increase in the Perapart sum and chromatic aberration due to this.

In addition, by selecting the ν rise of the first lens and the second lens, the chromatic aberration of the magnification can be achieved, and the fifth lens, which is the fifth group, can be used as a convex lens with the surface with a small radius of curvature facing the horizontal side. This is a book that avoids the negative effects on field curvature and distortion.

Such a lens is shown in FIG.
? Start from the object side to show the formation! The 1st lens group is a concave meniscus lens with its convex surface facing the object, the 2nd lens is a biconvex lens with the surface with a small radius of curvature facing the object, and the 3rd lens in the 3rd group is a concave meniscus lens with its convex surface facing the object. A biconcave lens with the surface with a small radius of curvature facing the object side, the 4th 4th percentile
The @5 lens, which is the fifth group, has a surface with a small radius of curvature facing the image side.
In the lens of *S, yrl, "211.・r)o
: Radius of curvature d1, d2, ... d of each surface in order from the object side
9: Surface spacing n1, n2,... of each surface in order from object #- side
ns: refractive index of each lens ν1, ν2, . . . Atsube number f1 of each lens: focal length of the lens ft2. x: 60 < ν1 < when the composite focal length from the 1st lens to the 3rd lens
L75 (n2':2
) 1.70 (n4 town 3) 1
．． 62 <ns', 4
)48 〈 ν2 Town 5)-Ll
7 <'/f t2. & (-1,127
6) d4+d7+d6+dg (0,18f
The conditions of <7) are satisfied.

First, the overall structure of the lens system (concave lens, which has the effect of lengthening the pack focus, tends to cause chromatic aberration of magnification, and the larger the chromatic aberration of magnification that occurs here, the more the lens needs to correct it. It is difficult to do this, so it is necessary to suppress this as much as possible.Therefore, the condition is that the number of Atsubes in the first run is 7.

Half angle of view 33Pi! In order to properly correct the astigmatism up to the point (), it is better to make the Perapart sum less than 0.15; if it is larger than this, the astigmatism difference will become large.In order to make this Verapart sum small, the following conditions must be met: '2) < 3) Town 4) must be satisfied.

Furthermore, if the condition <OvC, the chromatic aberration becomes negative, so it is necessary to increase the Abbe number of the convex lens or to decrease the Abbe number of the concave third lens.

However, if the Atsube number of the concave third lens is made small, the perapearl sum becomes large, so it is necessary to satisfy condition (5).

In the above-mentioned known example, when trying to increase the light blue, the high Hh incident light lI4 ends up being flared, but the flare due to this comatic aberration is related to the distribution of honey expressed by u'/ft25. I'm here. Condition (6) is a condition for correcting this coma aberration, and in order to correct coma aberration, which increases as the angle of view increases, it is better to be as large as this value, but if the upper limit is exceeded, the distortion becomes negative. , of the target! ! It is very difficult to correct it on site. If the lower limit is exceeded, Hh, which has a particularly high incident height, becomes 7 rare, and if you try to correct the distortion by reducing the value of '/ft2, distortion and chromatic aberration will become negative. In retrofocus lenses, this will be negative. To reduce this distortion, it is necessary to increase the surface spacing of the front group or to reduce the surface spacing of the rear group. Condition <7) is related to this.

By increasing d5, d4, and d5, it is possible to increase the distortion fj in the positive direction, but all of them result in a large lens diameter, which goes against the requirement to make the lens system compact. Therefore, the surface spacing of the rear group d6+d7-)-a,
+d, must be small (if necessary, condition 7) must be satisfied in order to push the distortion to less than 12 inches.

Examples of the present invention that satisfy the above conditions are as follows: Mizuko Example 1 t:3. s, f = too, half image MW - 33° back focus fB = 1253 fs, u = -86,96 f/ft2.5 = -1,150
r1= 190.00 dl= 6.2 nt
-'1.55963 1'+=61.2r2;! S4.
OU d2= 63.0r5= 95JOd! l
= 13.2"2=1.734UO'2=51.5
ra=-210,60d4=323r5: 5
0. OU ds = 7.4 1g = 1.71736
1'5=29.5r6- 20&00 d6=
1.9'7=-230,, od7=67 na
=1.71300 shi4=53.8r=-5a2tl
da= (14r = −4(30, g□ d
y=7. On5=1.63854 ν5=55.
4r = -70,55 0 Example 21: 3.5, f = I U U, half angle of view W =
33 Back focus fB=125.6 ft2. s = -87,00, f/f1.2. s =
-1,149r1= 190.00 dl= 6
2 n+=1.55963 si1=61.2r2=
54.00 d2= 63. .

r5=960U dg=13. (J
T12=1.74320 ν2=49.3r4
:: 215.70 d4= : U2.0r
s=-50, OLI ds=7. fi Tl5
=1.72825 shi3=23.5r6=228
．． 5+) d6= 2.1r7- 200. +)O
d7= 6Ll n4=1.721 River U I'4
=50.2r6=54.70d6= (1
,45rq--400,t)Odq=7. Un
5=1.64850 ν5=530'1F -71,
, 68 f-1, the Seidel aberration coefficients in the *m example above are as follows. However, P is the peak of Petzval, S is the peak of spherical aberration, and C is the peak of coma aberration.
D represents the peak of distortion, respectively.

Seidel aberration coefficient P 5CAD 1 0.189 0.034 0. U64 0.12
1 0.5892-0.664 -5509-IL39
9-1045-0.7443 0.444 6.28
3 4.948 3.897 3.4194 0.20
1 2.574 0.164 0L) 113 001
35-0.835-12.748-5.587-2.4
49-1.4396 -0.201 -3.061
-3.831 -4.796 -6.2! '567-0
．． 181 0.301 0.631 1.321 2
．． 38680.741 3.794 1.670 0
．． 735 0.6509-0.097 -0.1320
0.027-0.1136 0.17810 α5
52 10.145 5.411 2.886 1.8
34Σ 0.149 1.793 1. +198 0
．． n44 0630 Actual m Example 2 Seidel aberration coefficient P S CA, D I 0.1B9 0.034 0. U64 012
1 0.5R92-0,665-5511-2,411
o -1,045-0,74430,4446,227
4,9133,8763,40940,19B 2
．． 522 0.147 0. UO90,1H25-0,
843-12, 902-5629-2, 456-1, 4
396-0,184-'L879-3.632-4.5
F33°-6, tl l 57-0.209 0.2
24 0.5to 1.163 2.1?58 0.
765 4.155 1.855 0.828 0.
7129-0.098-α1J21 0. (12B
-0,0370,178100,5499,9935,
2672,7761,752Σ 0.146 1゜8
42 1.123 0.652 0.62911E2 and FIG. 3 show the aberration curves of Example 1, and FIGS. '4 and δ show the aberration curves of Example 2. In each of the examples, the sagittal ray of astigmatism does not become excessively positive, and even when the angle of view becomes high, the coma aberration is maintained, and especially when the incident height is high, Hh
The upward slope of the curve is extremely small. Also, the chromatic aberration of magnification is well dispersed for both the d-line and the g# and C-lines up to high angles of view.

[Brief explanation of drawings]

FIG. 1 is a sectional view of the structure of the retrofocus lens of the present invention, FIGS. 2 and 3 are aberration curve diagrams of actual tIA example 1, and FIG.
5 are aberration curve diagrams of Example 2. Patent applicant: Ricoh Co., Ltd. Figure 2 (ψ Astigmatism Distortion 1%) Astigmatism Distortion Figure 3 W = 33° - - - C line calculation Figure 5 W = 33° W = 30° -25 W=8 1--g line-・-〇 line

Claims (1)

[Claims] From the object side: The first lens group is a concave meniscus lens with a convex surface facing the object side, and the second lens group is a concave meniscus lens with a surface with a small radius of curvature facing the object side. Biconvex lens, 3rd
In detail, the third lens is a biconcave lens with the surface with the smaller radius of curvature facing the object side, and the fourth lens group is the 5th fF.
The fifth lens is a 5-element lens consisting of a convex meniscus lens with 5 surfaces with a small radius of curvature facing toward the side. ”” rto: l[K each F from the object side
lll ratio of i'14d,,d2,...d9: Surface spacing Js of each surface from the object side to Ni t12,...ns: Refractive index of each lens ν1. ν2, ... ν5: Atsube number f1 of each lens: Focal length steepness fl of the 1st lens, 2.5: 60 x ν111) 1.75 <n2<2)1.70<na
<3) 1.62 <ns 4)
48 < C2-5) -1,17< f/ftzx (-1,t 2 7
6) d4+d7+da+d9 < 0.18 f
Retrofocus type lens that satisfies the conditions of 77)