JPH01205117A - Rear converter lens - Google Patents

Abstract

PURPOSE:To make a rear converter lens free from influences caused by changes in temperature and moisture by forming each of positive and negative lens of the four lenses of a plastic material. CONSTITUTION:This rear converter lens is constituted of four-group four-piece lenses of, from the object side to the image side, the 1st-4th lenses, of which the 1st and 3rd lenses are positive lenses and the 2nd and 4th lenses are negative lenses. Of the four lenses, one each of positive and negative lens is formed of a plastic material. Moreover, the lenses are caused to satisfy the conditions of inequalities I-VII. The Ri and Ni and vj of the formulae respectively represent the radius of curvature of the i-th lens surface from the object side, the refractive index to the line (d) of the j-th lens and Abbe's number. Since the focal point moving direction of the positive lenses caused by changes in temperature and moisture is opposite to that of the negative lenses, influences of the changes in temperature and moisture can be offset.

Description

[Detailed description of the invention] (Technical field) The present invention relates to a rear converter lens.

(Prior art) A rear converter lens is known as a lens that is attached to and removed from the rear of the main lens to change the focal length of the entire system, and in recent years it has come to be used as a built-in lens in lens shutter cameras. Conventionally, as a rear converter lens with a large variable power ratio, Japanese Patent Application Laid-Open No. 62-153
One disclosed in Japanese Patent No. 912 is known. That is,
This publication discloses a zoom lens that has a four-group, four-element structure and achieves a variable power ratio of 1.9.

However, since this rear converter lens has two positive lenses out of four lenses made of plastic,
The problem is that the focal point shifts significantly due to changes in temperature and humidity.

(Objective) The present invention has been made in view of the above-mentioned circumstances, and its object is to provide a lens that is less affected by changes in temperature and humidity and has a large zoom ratio.

The present invention provides a new rear converter lens that is compact, inexpensive and can be realized.

(composition) The present invention will be explained below.

The rear converter lens of the present invention is a rear converter lens that changes the focal length of the entire system by being attached to and detached from the rear of the main lens system. It has a four-element configuration in four groups arranged in order.

The first lens is a positive lens, the second lens and the fourth lens are negative lenses, and among these four lenses, the positive lens 1
and one negative lens are made of plastic.

When the radius of curvature of the first lens surface from the object side of this rear converter lens is Ri, the refractive index of the j-th lens with respect to the d-line is Nj, and the Abbe number is νj.

These are (1) 0.8 < R2/R3 < 1.1 (
II) 0.8 < R6/R7 < 2.5 (I
II) 0.9 <R4/R'5< 5.0
(m (N1+N3)/2 < 1.6m
1.7 < (N2+N4)/2(VI)
l vl-v 21 < 12 (VII)
The condition l v3-v41 < 17 is satisfied.

As described above, the rear converter lens of the present invention has a lens configuration of four lenses in four groups, and two lenses are made of plastic, and one of these plastic lenses is a positive lens and the other is a negative lens. . The direction of focus movement due to temperature and humidity occurs in opposite directions for positive and negative lenses, so by combining positive and negative plastic lenses in this way, the effects of temperature and humidity cancel each other out. It acts like this.

Now, the focal length conversion method using a rear converter lens is a method that expands the focal length by placing a lens system with negative power behind the main lens. Due to the negative power of Among them, the light beam passing through the peripheral portion of the main lens system lens is subject to a strong diverging effect of the rear converter lens, and coma aberration tends to worsen.

Among the above conditions 0) to (VII), condition (I) prevents comatic aberration, spherical aberration, and This is a condition for maintaining a good Petzval sum. If the upper limit is exceeded, the divergence effect of the air lens becomes too strong, causing coma aberration to worsen, spherical aberration to become excessive, and the Petzval sum to become negative, making it difficult to maintain an appropriate value. Preservation becomes recollection. On the other hand, if the lower limit is exceeded, the convergence effect of the air lens becomes too strong, comatic aberration worsens, and spherical aberration becomes under-corrected, making it difficult to correct.

Condition (II) is a condition for maintaining good spherical aberration under condition (r). The spherical aberrations generated in the air lens formed by the image side surface of the second lens and the object side surface of the second lens and the air lens formed by the image side surface of the third lens and the object side surface of the fourth lens have a complementary relationship. Therefore, if the upper limit of this condition (II) is exceeded, the spherical aberration becomes over, and if the lower limit is exceeded, the spherical aberration becomes under, and in either case, it becomes difficult to correct the aberration.

Condition (HI) is a condition for maintaining good distortion, and if the lower limit is exceeded, the occurrence of positive distortion becomes large. If the upper limit is exceeded, distortion is good, but higher-order aberrations such as off-axis curvature of field sag, which is not preferable.

Conditions (IV) and (V) are conditions for keeping the Petzval sum appropriate and improving the balance of the off-axis image plane.If any of these conditions are violated, the 5 Petzval sum will be too small and the off-axis image plane will be The external image plane is overcorrected.

Conditions (VI) and (VII) are conditions for maintaining good axial and off-axis chromatic aberrations. In particular, (VI) is concerned with axial chromatic aberration, and condition (VII) is concerned with off-axis chromatic aberration. If these conditions are not met, it is impossible to maintain a good balance between on-axis and off-axis chromatic aberrations.

In the present invention, one of the positive lenses and one of the negative lenses are configured as a pair of plastic lenses.

Conventionally, a spacer ring is used to maintain the distance between the lenses, but the spacer ring can be omitted by integrally forming a flange portion around the periphery of the plastic lens.

(Example) Specific examples will be given below. The following two types of main lenses are envisaged to be combined with the embodiment rear converter lens of the present invention.

These two types of main lenses A and B each have a configuration of 4 elements in 3 groups, and the radius of curvature of the i-th lens surface from the object side is ri.
, the interplanar spacing is di, the refractive index of the j-th lens with respect to the d-line is nj, and the Abbe number is vj, these values are given as follows.

Main lens A: f=36. F+to=3.6, 2ω=6
2 degrees, M=27i ri di j
nj vjl 10.411 3.9
1 1.7433 49.222 21.765
0.9 3 -53.0 0.93 2 1.69895
30.054 10.03 1.0 5 20.691 2.72 3 1.744
44.96 -12.39 1.44 4 1.5
1823 58.967-59.39 1.0 8ol) (aperture) f is the focal length of the main lens A, and FNO is the F number.

2ω represents the angle of view, and bf represents the back focus.

FIG. 13 shows the lens configuration of the main lens A, and FIG. 14 shows an aberration diagram regarding the main lens A.

Main lens B: f=36. FIlo"3.6.'2ω=
61.3 degrees, bf=27.9i ri di
j nj vjl 10.87
4 3.154 1 1.7995 42.34
2 26.639 0.809 3 -87.304 1.494 2 1.75
52 27.534 10.695 1.1
31 S 26.718 2,77 3 1.8
061 40.736 -12.48 0.9
44 4 1.54072 47.27 -10
2.075 0.8 3oo (aperture) f is the focal length of main lens B, FMO is the F number.

2ω represents the angle of view, and bf represents the back focus.

FIG. 15 shows the lens configuration of the main lens B, and FIG. 16 shows an aberration diagram regarding the main lens B.

Six specific examples are listed below.

In each example, the radius of curvature of the i-th lens surface from the object side of the rear converter lens is R1°, and the surface spacing is Di.
, the refractive index for the d-line of the j-th lens is Nj, and the Abbe number is vj. Also, F is the focal length of the entire system in combination with the main lens, FNO is the F number, 2ω
indicates the angle of view, BF indicates the back focus, and M indicates the variable magnification ratio.

Moreover, in Examples 1 and 2, the third. The fourth lens was a plastic lens made of polycarbonate, and in Example 3, the fourth lens was made of polycarbonate, and the fourth lens was a plastic lens made of PMMA.

Further, in Example 4, the second lens is made of PMMA, and the third lens is made of polycarbonate, and in Example 5.6, the first lens is made of PMMA and the third lens is made of polycarbonate. The fourth lens is made of polycarbonate.

Furthermore, in Examples 1, 2, 3, and 4.6, aspheric surfaces are employed for some lens surfaces. This aspherical surface has a well-known aspherical function when the X-axis is taken in the direction of the optical axis and the Y-axis is taken in the direction perpendicular to this:
+A 4Y 4 +A 6Y 6 +A llY 1
1, and when the paraxial radius of curvature is R, C=(1/
R) with a conic constant of 1 and a higher-order aspherical coefficient A4. As,
It is specified by As.

Example 1 As shown in FIG. 1, the rear converter lens is combined with the main lens A in this example. The values of each parameter for an aperture of 10 or less are as follows.

r8 (aperture) =oo d8=0.389i
Ri Di j Nj
Vjl 30.92 2.7
1 1.5927 35.452-12.148
0.38 3-12.809 1.44 2 1.922
5 35.954 15.367 0.112 5 14.39B 3.41 3 1.58
5 29.36-25.775 0.5 7”-14,5912,4141,58529,38-
42,207 Aspherical surface (R7): ni=-0,125748,A,=4
．． 269434XIO-s.

Aa”3.561153ylO-7,A,=-1,28
4581XIO-”F”68. FNO=6.8,2ω”
34-7 degrees, BF=37.9. M=1.89R2/R3
= o, Flp2￥, R6/R7,/nItke, R
4/R5=106n4, (N1+N5)=/, r t
J6r, l v 1-v 2 l = o, jI 1
ν 3− ν 4 1 =O(/J2rN4
/=≧, = i, 7r31 FIG. 2 shows an aberration diagram of the combination with the main lens A regarding this Example 1.

Embodiment 2 As shown in FIG. 3, the rear converter lens is combined with the main lens A in this embodiment as well. The values of each parameter below the aperture lO are as follows.

R8 (aperture) 200d8=1.15 i Ri Di j Nj
Vjl 28.977 L91 1 1.
5927 35.452-12.285 0.41
8 3-12.545 2.18 2 1.9225
35.954 14.793 0.12 5 14.83 2.85 3 1.585 2
9.36-22.384 0.435 7'-14,7082,4741,58529,38-
48,421 Aspherical surface (R7): to=-0,403139,A,=1.
446702xlO-'.

AG"1.088594X10-', Aa=-1.9
88352 Kari 04F”68.FNO”6.8.2ω=3
4. '5 degrees, BF=3'5.6. M=1.89R2/R
3=a, 97';'J, R6/R7=/, rz
or, R4/R5= o, r97r, (N1+N5)
= /, rgFj”A-, ly 1-v 2 l
= a, tt I v3-94 l =O(N2r
N4)/l=/nr37r FIG. 4 shows an aberration diagram of this embodiment 2 in combination with the main lens A.

Embodiment 3 As shown in FIG. 5, the rear converter lens is combined with the main lens A in this embodiment as well. The values of each parameter for an aperture of 10 or less are as follows.

R8 (aperture) = oo d8 = 2.2i Ri
Di j Nj Shira 1-204.69fu 2,46 1 1.585
29.32” -9,6160,44 3-10,8941,S 2 1.9225
35.954 179.978 0.22 5 37.832 2.8 3 1.51742
52.156 -14.887 0.24 7"-11,0221,241,4915457,83
8-124,39 Aspherical surface (R2): Knee 0.029033. A4=9.
115926xlO-'.

A6=-1,213055xlO-', A,=3.81
6452X10-' Aspherical surface (R7): = 0.03
48. A, =9.289292xlO-'.

Ag"-2,071704XIO-', Aa"8.2
04045X 10-'F=68. Fso"6.8,
2ω: 35 degrees, BF=37.7. M=1.89R2/R
3=tr, 1g27, R6/R7=7.3ro7
, R4/R5=t, 7r7z, (N1+N3)2/,
Otsu! 7z2/ , I 11-v 21 = (,
12, ly3-v41 = j, to g (tJ
2tN/2=/, n o7oL Figure 6 shows this example 3.
The aberration diagram of the combination with the main lens A is shown.

Embodiment 4 As shown in FIG. 7, the rear converter lens is combined with the main lens B in this embodiment. The values of each parameter for apertures below 11 are as follows.

R8 (aperture) = ood8 = 0.866 i Ri Di j Nj
Vjl-32,8792,3911,5182
358,962-8,7770,536 3'-8,3321,8321,49161,44
32,3320,122 5” 19.844 3.6 3 1.585
29.36 -7.962 0.144 7 -8.999 1.69 4 1.9326
27.928-121.369 Aspherical surface (R3): K”0.070378.A4”-1
,438723x 10-5゜A6=-1,59145
9AIO-', Aa=-1.145675'lO-'Aspherical surface (R5): to=2.043029. A4=-5,
374725xlO-'.

AG=-2,917522710-6,Aa=5.27
2315. xlO-'F”68.FNo:6.8,2ω
=35 degrees, BF=40.1. M=1.89R2/FI3
= /-Of? ';', R6/R1=l), Ig'
4J, R4/R5-t, (x93, (N1+N5
)=Lrr/12, lv1-v2l=
2.4(11-, l v 3-v 4 l = '3g,
(n2fNlr)/2=/, 2ng FIG. 8 shows an aberration diagram of the combination with main lens B regarding this Example 4.

Embodiment 5 As shown in FIG. 9, the rear converter lens is combined with the main lens B in this embodiment as well. The values of each parameter for apertures below 11 are as follows.

r8 (aperture) = OOd8 = 3.331 i Ri Di j Nj
νj1 246.246 2.6 1 1.5
85 29.32 -10.155 0.432 3 -10.867 0.84 2 1.883
40.84 31.317 0.335 5 21.718 3.02 3 1.5
4814 45.826 -25.039 0.4
33 7 -11.103 1.31 4 1.5
85 29.38 -19.619 F”68.Fso”6.8, 2ω=35.3 degrees, BF=
38. M=1.89R2/R3=ρ, y3+(-,
R6/R7=2,2rr2, R4/R5=744
2-, (Nl+N5)= /・Ft6?7,1ν1-
ν21=//, r11shi3-shi4l=/1. t2
−, /~2+N6λ/2 near, 7j order 1θ diagram,
An aberration diagram of the combination with main lens B regarding this Example 5 is shown.

Embodiment 6 As shown in FIG. 11, the rear converter lens is combined with the main lens B in this embodiment as well. Aperture 11
The values of each parameter below are as follows.

r8 (aperture) = ood8 = 2.42 i Ri Di j Nj
v:41 131.502 3.227 1 1
．． 585 29.32 -10.424 0.54 3 -10.348 0.872 2 1.92
25 35.954 33.12 0.2 5 25.387 2.95 3 1.5
927 35.456 -19.357 0.5 7'-14,6551,46741,58529,3 Aspherical surface (R7): ni=-0,241337,A<=1.
874211xlO-s.

As=-1,168116xlO-', Aa"3.03
5541X10-8F=68. FNo=6.8.2(,
1=35.1 degrees, BF=38.5. M=1.89R2/
R3= y, ooti, R6/R7= /, j
2oF: , R4/R5= /, jO+6, □=/,
jffJr, lv1-v21 = 1. lr
* l v 3-v 4 l = l/, Ku,
(~2?mJ/2 = / nr321-12th
The figure shows an aberration diagram of this Example 6 in combination with main lens B.

(Effects) As described above, according to the present invention, a novel rear converter lens can be provided.

As mentioned above, this rear converter lens achieves a high variable power ratio, but since it has a small number of lenses (four lenses in four groups), it can be realized compactly and can be built into the camera body. Furthermore, since two of the four lenses are made of plastic, it is lightweight and can be realized at low cost. Also 2
As is clear from the aberration diagrams of each example,
Even in combination with the main lens, aberrations can be well corrected.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing a lens configuration in combination with the main lens of Example 1 of the present invention, and FIG. FIG. 3 is a diagram showing the lens configuration in combination with the main lens of Example 2 of the present invention, FIG. 4 is an aberration diagram regarding Example 2, and FIG. 5 is an aberration diagram regarding Example 1. 6 shows the aberration diagram of the above-mentioned Example 3, and FIG. 7 shows the main lens of Example 4 of the present invention. FIG. 8 is an aberration diagram regarding the above-mentioned Example 4, and FIG. 9 is a diagram showing the lens configuration in combination with the main lens of Example 5 of the present invention. , FIG. 10 is an aberration diagram related to Example 5, 1I
The figure shows the lens configuration in combination with the main lens of Example 6 of the present invention, FIG. 12 is an aberration diagram regarding Example 6, and FIGS. 13 and 14 show the main lens A. 15 and 16 are diagrams for explaining the main lens B. FIG. （＼）
Turtle 9 ゝq
q≧) ta
f) c′ mi ((＞guN mi)
('Satoson N

Claims (1)

[Claims] A rear converter lens that changes the focal length of the entire system by being attached to and detached from the rear of the main lens system, the first to fourth lenses being attached in this order from the object side to the image side. It is composed of four lenses arranged in four groups, the first lens and the third lens are positive lenses, the second lens and the fourth lens are negative lenses, and among these four lenses, the positive lens 1
and one negative lens are formed of plastic, the radius of curvature of the i-th lens surface from the object side of the rear converter lens is Ri, and the refractive index of the j-th lens with respect to the d-line is N.
j, Abbe number is νj, these are (I) 0.8<R2/R3<1.1 (II) 0.8<R6/R7<2.5 (III) 0.9<R4/R5 <5.0 (IV) (N1+N3)/2<1.6 (V)1.7<(N2+N4)/2 (VI) | ν1 − ν2 | < 12 (VII) | ν 3 − ν 4 | < 17 Condition A rear converter lens that satisfies the following.