JPH02191907A - Front stop triplet lens - Google Patents

Abstract

PURPOSE:To obtain a lens which has less coma, a good contrast, F3.5, and 54 deg. field angle and is suitable for a video camera with a simple constitution by providing a stop on the object side of a first group of a lens system consisting of three groups of three lenses arranged in order from the object and satisfying prescribed conditions. CONSTITUTION:The lens system is constituted of the first group consisting of a double convex lens whose face having a shorter radius of curvature is directed to the object side, the second group consisting of a double concave lens, and the third group consisting of a convex meniscus lens whose convex is directed to the image side. These lenses satisfy conditions of inequalities I to V where f1, (f), d1, r5, SIGMAd1, n1, and gamma1 are the focal length of the first group, the resultant focal length of the whole of the system, the thickness of the double convex lens of the first group, the radius of curvature of the object-side face of the convex meniscus lens of the third group, the distance from a stop 20 to the image-side lens face of the convex meniscus lens of the third group, the refractive index of the double convex lens of the first group, and the Abbe's number respectively.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a front aperture triplet lens. This lens can be used as a photographic lens for video cameras, etc.

[Prior Art] In photographic optical systems such as video cameras, a color filter is placed in front of a solid-state image sensor, but if the distance and exit angle between the light-receiving element array surface of the solid-state image sensor and the color filter are large, so-called color distortion occurs. It is known that deviations occur.

For this reason, for example, a method to reduce the exit angle may be to reverse the relationship between the object and the image in a telecentric optical system. In this way, the principal ray at the exit angle becomes parallel to the optical axis, and color shift does not occur.Furthermore, by disposing the aperture in front of the lens system and bringing it closer to the front focal point, color shift can be reduced.

If the diaphragm is placed inside the lens system, the front and back of the lens system are separated due to the construction of the lens barrel, which tends to cause eccentricity, but if the diaphragm is placed in front of the lens system, it becomes a single lens barrel and can be assembled. However, as the angle of view increases, the diameter of the rear lens increases and aberrations are more likely to occur.As the F number decreases, comatic aberration of the chief ray becomes large when the image height is positive. As a result, imaging performance deteriorates.

In addition, each solid-state image sensor has a fixed pixel size, and when a spatial frequency component higher than that size is incident, if the imaging system has the ability to image the high frequency component, moiré will appear on the playback screen. Stripes appear. To prevent this, a low-pass filter is usually used to cut high frequency components. Since the low-pass filter is a parallel flat plate with a predetermined thickness, the contents of the lens system differ depending on its insertion position.

[Problem to be solved by the invention] When a 1/2-inch solid-state image sensor is used for the imaging plane, the imaging range is at most 8 mm, and if the half angle of view is 240 mm, the focal length is about 9++++a. Become.

Conventionally, as an imaging lens with a front aperture, the
105, Japanese Patent Publication No. 60-53847, Japanese Patent Application Laid-Open No. 61-77816, etc., but all of them have large coma aberration or It cannot be put to practical use because there is a difference in point spacing.

The present invention has been made in view of the above-mentioned circumstances, and its purpose is to provide a triplet-type lens that can withstand the usage of the above-mentioned video cameras, etc.
The objective is to provide a front aperture triplet type lens with a number of 3.1, a half angle of view of 24'', less flare due to coma aberration, and good contrast imaging performance.

[Means to solve the problem] The present invention will be explained below.

Two types of front aperture triplet lenses are proposed herein, as claimed in claims 1 and 2.

The triplet type lens according to claim 1 includes FIGS. 1, 4,
As shown in FIGS. 7 and 10, the first to third groups are arranged in this order from the object side to the image side, and the aperture 20 is arranged on the object side of the first group. .

A triplet type lens according to claim 2 is shown in FIG. 13.

As shown in FIGS. 16 and 19, the first to third groups are arranged in this order from the object side to the image side, and
Parallel flat low-pass filters L and P on the object side of the first group
, F and an aperture 20.

In both of the triplet lenses according to claims 1 and 2, the first group includes a biconvex lens 10 with a radius of curvature of the water surface facing the object side;
The group is a biconcave lens 12, and the third group is a convex meniscus lens 14 with a convex surface facing the image side, and is composed of three lenses in three groups.

In the triplet type lens according to claim 1.

The focal length of the first group is f1, the composite focal length of the entire system is f, and the thickness of the biconvex lens lO of the first group is d8. The radius of curvature of the object side surface of the convex meniscus lens 14 in the third group is r, the distance from the aperture 20 to the image side lens surface of the convex meniscus lens 14 in the third group is Σdt, and the refraction of the biconvex lens 10 in the first group is When the ratio and Atsube number are n1 and ffl, these are (1-I) 1.90 < fIL <
2.13(1-II) 0.125f<
dt < 0.182f(1-III)
−1,72f < rs < −1,
34f(1-IV) 0.509f <X
:dt<0.589f(1-V) 175
The triplet lens according to claim 2, characterized by the following conditions: <rH< 1.90.40 <v l < 51.

The focal length of the first group is fI, and the combined focal length of the first and second groups is f1! , the combined focal length of the entire system is f, the thickness of the biconvex lens in the first group is 6, the distance between the surfaces of the biconvex lens in the first group and the biconcave lens in the second group is d8, the refractive index of the biconvex lens in the first group and Atsube number is nly 乍, these are (2-I) 1.95 < fI
fl < 2.22 (2-11)
0.018 < fIL, s < 0.067
(2-III) 0.181f (ds+d
x < 0.204f(2-IV) 1
．． 79(n, <1.90. The following conditions are satisfied: 40<tsu, <51.

[Function] In the triplet lens of claim 1, one condition (1-
I) defines the range of refractive power of the biconvex lens 10 of the first group, and is an important condition for refractive power distribution of the lens.

In order to reduce the Petzval sum, fIf should be a large value, and the first group will inevitably have a biconvex lens shape, but if the upper limit of condition (1-1) is exceeded, the Petzval sum will become small. Therefore, the meridional rays at the periphery become negative. Moreover, when the lower limit is exceeded, the astigmatism difference becomes large and peripheral performance deteriorates.

In order to reduce the astigmatism difference to the periphery and make the image plane flat, the first group of biconvex lenses 10 and the second group of biconcave lenses 12 are used.
It is preferable to reduce the distance between the two convex lenses 10 and 10. This causes the image plane to tilt negatively, but this tilt can be corrected by increasing the thickness of the biconvex lens 10 of the first group.

Condition (1-II) defines the conditions for this correction; if the upper limit is exceeded, the image plane becomes too positive, and if the lower limit is exceeded, the negative inclination of the image plane cannot be sufficiently corrected.

Condition (1-Ill) is the convex meniscus lens 1 of the third group.
The range of the radius of curvature of the object-side lens surface of No. 4 is determined. The shape of the third group is preferably a convex meniscus lens with a convex surface facing the image side. When the upper limit of condition (1-Ill) is exceeded, the astigmatism difference increases, and when the lower limit is exceeded, the entire image plane becomes negative.

In order to reduce flare due to comatic aberration, the overall length of the lens, ie, the length from the aperture 20 to the AM surface of the lens system, must be set appropriately. The zero condition (1-IV) indicates this range. Generally, it is advantageous to increase the total length of the lens to eliminate flare, but if it exceeds the upper limit of one condition (1-IV), the aperture efficiency will decrease.

When the lower limit is exceeded, flare increases.

In order to maintain the Petzval sum at about 0.35, it is necessary to increase the refractive index of the convex lens system, and condition 5 (1-V) defines the range of the refractive index of the biconvex lens 10 of the first group. If the upper limit of the refractive index and the lower limit of the Atsube number are exceeded, there is no available glass, and if the lower limit of the refractive index is exceeded, the Petzval sum increases and chromatic aberration of magnification increases. Furthermore, if the upper limit of the Abbe number is exceeded, a high refractive index cannot be obtained.

In the triplet lens according to claim 2, the condition (2-
Similar to the above condition (1-I), I) defines the range of refractive power of the biconvex lens 10 of the first group.

In order to reduce the Petzval sum, fIf
It is better for 1 to be a large value, and the first group will inevitably have a biconvex lens shape.However, in the case of an end structure in which low-pass filters L, P, and F are arranged on the object side of the first group, the condition (2- If the upper limit of I) is exceeded, the Petzval sum becomes too small and the meridional ray in the peripheral area becomes negative. Moreover, when the lower limit is exceeded, the astigmatism difference becomes large and peripheral performance deteriorates.

Parameters f/fx, z of condition (2-II) are usually set to negative values in order to reduce the Petzval sum, and their absolute values are increased, but in the triplet type lens of claim 2, the above-mentioned By setting the parameter to a positive and small value, the incident principal ray is prevented from becoming a large flare when the object height is negative, and even if the aperture efficiency is increased at the outermost periphery of the half angle of view of 24 degrees, no flare occurs. This condition is necessary in order to obtain an image with good contrast6
When the upper limit of condition (2-E) is exceeded, both the sagittal and meridional rays tend to become negative, and when the lower limit is exceeded, coma aberration occurs, and distortion becomes negative and large.

In order to reduce astigmatism to the periphery and make the image plane flat, it is best to make the distance between the lens surfaces of the first group's biconvex lens and the second group's biconcave lens narrower, resulting in a negative image plane. In order to correct this, the thickness of the biconvex lens in the first group is increased, but 1
Condition (2-III) indicates the range; when the lower limit is exceeded, the meridional becomes too positive, and when the upper limit is exceeded, the opposite is true. Therefore, the range of condition (2-111) is good.

In order to keep the Petzval sum around 0.35, it is necessary to increase the refractive index of the convex lens system, and one condition (2-IV) is:
This defines the range of refractive index of the biconvex lens 10 of the first group. When the upper limit of the refractive index and the lower limit of the Atsube number are exceeded, there is no available glass, and when the lower limit of the refractive index is exceeded, the Petzval sum becomes large and chromatic aberration of magnification increases. Furthermore, if the upper limit of the Abbe number is exceeded, a high refractive index cannot be obtained.

[Example] Seven specific examples are listed below.

Examples 1 to 4 are examples of the triplet type lens according to claim 1, and Examples 5 to 7 are examples of the triplet type lens according to claim 2.

In Examples 1 to 4, f is the composite focal length shield of the entire system, ω is the half angle of view, fI is the focal length of the Xi-th biconvex lens, P is the Petzval sum, ro is the radius of curvature of the aperture 20, and d , is the distance between the aperture and the object-side lens surface of the biconvex lens 10, rt(
iJ~6) is the radius of curvature of the first lens surface from the object side, dl is the distance between the first lens surfaces from the object side, nJ*
γj represents the refractive index and Abbe number of the lens in the fifth group for the d-line, and Σd represents the distance from the aperture 2o to the image-side lens surface of the convex meniscus lens 10 in the third group.

In addition, Section 1 which shows these examples. 4th. 7゜In Figure 10, the symbols P and F are low-pass filters, C,
F indicates a color filter, W and G indicate a cover glass of a solid-state image sensor; among these, color filters C, F,
Cover glasses G and G do not change performance even if you change their surface spacing, but low-pass filter L does.

The performance of P and F changes when the spacing between them is changed. r, (
C7-12) pdt (i=6-11), rlJ
p 9 J (j=4 to 6) indicates the radius of curvature of the image-side low-pass filter of the third group, etc., as shown in these figures.

Example 1 1:3.5. f=9. oo, (1+ “24”,
P”0.35.f/fs”1.981°Σd,=0.5
37f i r, d, j nj
vlOω (aperture) 0.683 1 5.455 1.186 1 1.7725
0 49.82 -8.904 0.372 3 -4.217 0.488 2 1.8727
0 32.14 5.554 0.238 5 -12.670 1.864 3 1.729
16 54.76-3.791 1.0 7 oo 1.0 4 1.51f
333 C4, 28001, 0 9ooL, 8 5 1.52700 C4,
010oo 2,0 11 0 0.7 B 1.516
33 84.212o.

FIG. 1 shows an optical layout diagram regarding Example 1.

FIG. 2 and FIG. 3 show aberration diagrams regarding Example 1.

Example 2 1:3.5. f-9,00,(1) =zli',
P”0.35.f/ft”1.965°Σd,=0.5
36f j rr dl J n”i
νJQoo (aperture) 0.586 1 5.616 L, Z41 1 1.804
00 46.62-9.850 0.368 3 -4.448 0.503 2 1.6889
3 31.14 5.595 0.237 5 -13.920 1.890 3 1.729
16 54.78-3.880 1.0 7 ao CO41,5163364,2
8 ■ 1.0 9 00 1.6 5 1.5
2700 64.010 oo
2.011 (X) 0.7
8 1.51633 64.212cl.

FIG. 4 shows an optical layout diagram regarding Example 2.

FIG. 5 and FIG. 6 show aberration diagrams regarding Example 2.

Example 3 1:3.5. f=9. oo, ω=24°, P=0.36
．． f/f, = 2.012°Σd, = 0.547f i ri d+ j nj'l
5Qoo (aperture) 0.597 1 5.699 1.289 1 1.8348
1 42.72-9.726 0.347 3 -4.581 0.527 2 1.7173
6 29.54 5.627 0.244 5 -14.421 1.922 3 1.729
16 54.76-3.919 1.0 7 oo1, 0 4 1.51633 64.2
8 oo 1.0 9 oo 1.6 5
1.52700 B4.010 oo2.0 11 oo O,761,51633
84,2 FIG. 7 shows an optical layout diagram regarding Example 3.

FIGS. 8 and 9 show aberration diagrams regarding Example 3.

Example 4 1:3.5. f=9. oo, ω=24°, P”0.35
．． f/f+”2,032°Σd,=o,561f i r, d, j nJ
ν.

Qoo (aperture) 0.587 1 5.97g 1.391 1 1.883
00 40.82-10.078 0.315 3 -4.831 0.586 2 1.7282
5 28.54 5.629 0.225 5 -14.753 1.949 3 1.729
16 54.76-4.045 1.0 7 oo 1,0 4 1.51633
64.28 oo1, 0 9 oo 1.6 5 1
．． 52700 64.010 00
2.0 11 00 0.7 6 1.
51633 64.2 FIG. 1O shows an optical layout diagram for Example 4.

FIG. 11 and FIG. 12 show aberration diagrams regarding Example 4.

In each aberration diagram, y' indicates the image height and the subject ratio is 3.
This is the value at 12.5+.

As is clear from each aberration diagram, the aberration curves of Examples 1 to 4 have little astigmatism at the maximum image height, good balance with the center, and a small amount of coma for a front aperture.

Next, Examples 5 to 7 will be given as examples of the triplet lens according to claim 2.

In these Examples 5 to 7, f is the composite focal length of the entire system, ω is the half angle of view, f is the focal length of the biconvex lens of the first group,
f1, 8 are the combined focal lengths of the first and second groups, P is the Petzval sum, rl (COI" 05) is the radius of curvature of each surface on the object side from the first group, d, (i = 01 to 05 ) is the interplanar spacing of the surfaces closer to the object than the first group -njyνj (j=
01, 02) represent the refractive index and Atsube number of the transparent plate located closer to the object than the first group, and these are determined as shown in the figure. r
□ (i = 1 to 6) is the radius of curvature of the first lens surface from the object side, di (i = 1 to 5) is the distance between the first lens surfaces from the object side, nj + νj (j = 1 to 3 ) indicates the refractive index and Abbe number for the d-line of the lens of the fifth group.

In addition, Section 13 shows these examples. 16th. In Fig. 19, symbols C and G are cover glasses, L, P, and F are low-pass filters, C and F are color filters, and V.

G indicates the cover glass of the solid-state image sensor; among these, cover glasses C, G, and color filters C, F.

The performance of the cover glasses W and G does not change even if the distance between their surfaces is changed, but the performance of the low-pass filters L, P, and F changes when the distance between their surfaces is changed. rc (i=7-10), d
.

(i:6-9), n4. y J (j''415) indicates the radius of curvature of the image-side color filter of the third group, etc., as shown in the above figure.

Example 5 1:3.5. f=9. oo, ω=24.4°, P
"0.35.f/fx" 2.109°f/ft, z: 0
．． 0170,dx”dx”0.191fi
rt ds j nJ
νj01 oo O,5
011,5163364,202000,5 03oo 1.0 02 1.518
33 B4.204 cw)
0.505cX) (aperture) 0.5241
5.568 1.448 1 1.83
481 42.72 -8.723 0.
2683 -4.499 0.487 2
1,71736 29.54 5.569
0.2465 -11.742 1.
904 3 1.72916 54.76
-3.879 1.07 φ
2.0 4 1.51B33 64.2
8 ω 4.0 9 00 0.7 5 1.5
1833 84.210 C-) FIG. 13 shows an optical layout diagram regarding Example 5.

FIG. 14 and FIG. 15 show aberration diagrams regarding Example 5.

Example 6 1:3.5. f=9.00° f7ft! ”0.0376 i　　　rl 02 o.

03 o.

04o.

05cx) (aperture) 1 5.434 2 -8.838 3 -4.556 4 5.371 5 -12.915 6 -3.985 7 ψ 8o.

9 o.

ω=24.4°, P=0.36. f/fl=2.05
1°, d, ÷ d, = 0.196f dl j nj VjO, 5
011,5163384,2 0,5 1,0021,5183364,2 0,5 0,627 1,47611,8040046,8 0,286 0,46421,6889331,1 0,257 1,82831,7291654,7 1, 0 2,04,1,5183364,2 4,0 0,751,5183384,2 FIG. 16 shows an optical layout diagram regarding Example 6.

FIG. 17 and FIG. 18 show aberration diagrams regarding Example 6.

Example 7 1:3.5. f=9. oo, ω=24.5″, P=0.
34. f/fl=2.117°f/ft, z”o, 06
41, d++d2”o, l95fi r(dI
j nl νj01 oo
O,5011,5183384,2026:jO,5 03φ 1.0 02 1.51633 64
．． 204 (X) 0.5 Q5oo (aperture) 0.786 1 5.702 1.490 1 1.8830
0 40.82 -9.644 0.261 3 -4.890 0.467 2 1.728
25 28.54 5.368 0.229 5 -12.813 1.890 3 1.729
16 54.76 -4.047 1.0 7 ao 2.0 4 1.5163
3 64.28 oo 4.0 9 00 0.7 5 1.5
1633 64.210 CO FIG. 19 shows an optical layout diagram regarding Example 7.

FIGS. 20 and 21 show aberration diagrams regarding Example 7.

In each aberration diagram, y' indicates the image height and is a value at a subject distance of 2.

As is clear from each aberration diagram, the aberration curves of Examples 5 to 7 have little astigmatism at the maximum image height, good balance with the center, and a small amount of coma for a front aperture.

[Effects of the Invention] According to the present invention as described above, a novel front aperture triplet type lens can be provided.

Since this lens has the above-mentioned structure, it has a simple triplet type structure but has good performance, and is suitable as an optical system for a video camera or the like.

[Brief explanation of the drawing]

FIG. 1 is an optical layout diagram regarding Example 1, FIG. 2 is an aberration diagram regarding Example 1, FIG. 3 is a coma aberration diagram regarding actual flow side 1, and FIG. 4 is an optical layout diagram regarding Example 2. layout drawing,
5 is a diagram showing various aberrations related to the second embodiment, FIG. 6 is a diagram showing coma aberrations related to the second embodiment, and FIG. 7 is a diagram showing the optical arrangement related to the third embodiment. 8 is a diagram of various aberrations related to Example 3, FIG. 9 is a diagram of coma aberration related to Example 3, FIG. 10 is an optical layout diagram of Example 4, and FIG. 11 is a diagram of various aberrations related to Example 4. 12 is a comatic aberration diagram regarding Example 4, FIG. 13 is an optical layout diagram regarding Example 5, FIG. 14 is a diagram of various aberrations regarding Example 5, and FIG. 15 is a diagram regarding Example 5. Coma aberration diagram, FIG. 16 is an optical layout diagram regarding Example 6,
FIG. 17 is a diagram of various aberrations related to Example 6, and FIG. 18 is
FIG. 19 is a coma aberration diagram for Example 6, FIG. 19 is an optical layout diagram for Example 7, FIG. 20 is a diagram for various aberrations for Example 7, and FIG. 21 is a coma aberration diagram for Example 7. 10. First group biconvex lens, 12. , second group biconcave lens, 14. ,, third group convex meniscus lens,
ruυ Kuni 1:3. ! ; Y'-4, (NZ Y'=4.θIZ Chiq Oral meridional coma aberration Saji Kurutsuma translation Kaya Sine Kanai 1:, 5J Sine condition Y'= 4.θIZ y'= 4.θ/Z Chi0 Meridional comatic aberration Sagittal coma Harumu I40 1:1.5 Do=4(σDededo=4ρAku'i?5 F) Akane sine system pestle v3% 圀(%) Sagittal huma aberration

Claims (1)

[Claims] 1. The first to third groups are arranged in this order from the object side to the image side, and an aperture is arranged on the object side of the first group, and the first group is a biconvex lens with a surface with a small radius of curvature facing the object side, the second group is a biconcave lens, and the third group is a convex meniscus lens with a convex surface facing the image side. The focal length is f_1, the composite focal length of the entire system is f,
The thickness of the biconvex lens of the first group is d_1, the radius of curvature of the object side of the convex meniscus lens of the third group is r_5, the distance from the aperture to the image side lens surface of the convex meniscus lens of the third group is Σd_i, When the refractive index and Abbe number of the first group of biconvex lenses are n_1 and ν_1, these are (I) 1.90<f/f_1<2.13 (II) 0.125f<d_1<0.162f(III) −
1.72f<r_5<-1.34f(IV)0.509f
<Σ_d_i<0.589f(V)1.75<n_1<
A front aperture triplet type lens, characterized in that it satisfies the following conditions: 1.90, 40<ν_1<51. 2. The first to third groups are arranged in this order from the object side to the image side, and a parallel plate low-pass filter and a diaphragm are arranged on the object side of the first group, The lens group consists of three elements: the second group is a biconvex lens with a surface with a small radius of curvature facing the object side, the third group is a convex meniscus lens with a convex surface facing the image side, and the first group is a convex meniscus lens with a convex surface facing the image side. The focal length of is f_1, the combined focal length of the first group and the second group is f_1_,_2, the combined focal length of the entire system is f, the thickness of the biconvex lens of the first group is d_1, the biconvex lens of the first group When the surface spacing of the biconcave lens in the second group is d_2, and the refractive index and Abbe number of the biconvex lens in the first group are n_1 and ν_1, these are (I) 1.95<f/f_1<2.22 ( II) 0.016<f/f_1_,_2<0.067(
III) 0.181f<d_1+d_2<0.204f(
IV) 1.79<n_1<1.90, 40<ν_1<51
A front aperture triplet lens that satisfies the following conditions.