JPS62220915A - Two-group zoom lens - Google Patents

Abstract

PURPOSE:To reduce variation of aberration while expanding a zoom ratio up to about 2.5 times, to compact a zoom lens, and to use the zoom lens for many purposes by composing the zoom lens of the 1st and the 2nd lens group in a specific array. CONSTITUTION:The zoom lens is placed in zooming operation by varying the on-axis gap between the 1st and the lens groups; and the 1st lens group consists of a lens system formed by arraying plural lenses having positive or negative refracting power in parallel and the 2nd lens group consists of the 1st lens 11 with positive refracting power, the 2nd lens 12 with positive refracting power, the 3rd lens 13 with negative refracting power, and the 4th lens 14 with positive refracting power in order from the object side to the image side. This constitution minimizes the movement of an image plane due to zooming while increasing the zoom ratio up to about 2.5 times; and high performance and compact constitution are obtained, the cost is reduced, and the lens is usable for many purposes.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to a two-group zoom lens used in a camera.

<Prior Art> Retrofocus type zoom lenses, in which a negative lens precedes them, have a large back focus and are therefore widely used as wide-angle zoom lens systems for single-lens reflex cameras.

<Problems to be solved by the invention> However, the 2-group zoom lens has a low degree of sunrise due to its design.
In particular, when aberrations are corrected at the wide-angle end and the telephoto end, it becomes difficult to correct the off-axis image plane at an intermediate focal length, so the zoom ratio is only about 2x.

Therefore, as a zoom lens, the zoom ratio is small.

<Means for Solving the Problems> The present invention was proposed in view of the above, and basically includes a lens group having negative refractive power from the object side toward the image side;
A second lens group having a positive refractive power, and zooming is performed by changing the axial distance between the second lens group and the second lens group, wherein the second lens group has a positive refractive power. , or a lens system in which a plurality of lenses having negative refractive power are arranged in parallel, and the second lens group includes a first lens having positive refractive power in order from the object side toward the image side,
It is composed of a second lens with a positive refractive power, a third lens with a negative refractive power, and a fourth lens with a positive refractive power. The lens is a negative lens with concave surfaces on both sides, and the fourth lens is a lens system whose bonded surface closest to the image side has a positive curvature toward the object side. With this configuration, the zoom ratio can be increased to approximately 2.5 times. To provide a two-group zoom lens that can minimize the movement of the image plane due to zooming while enlarging the lens to a maximum of 100 degrees, is compact with a high exterior design, and is suitable for multipurpose use such as low cost.

<Example> The present invention will be explained in detail below.

The two-group zoom lens of the present invention consists of a second lens group having negative refractive power from the object side toward the image side, and a second lens group having positive refracting power, and the second lens group has positive refracting power. In a two-group zoom lens that performs zooming by changing the distance between the two lens groups and the second lens group, the second lens group has a positive lens group,
Alternatively, the second lens group is constituted by a lens system in which a plurality of lenses having negative refractive power are arranged in parallel, and the second lens group includes, in order from the object side to the image side, a first lens 11 with positive refractive power and a second lens 11 with positive refractive power. 2 lenses 12. Third lens 13 with negative refractive power. Consisting of a fourth lens 14 with positive refractive power, the second lens 11 in the second lens group is a positive lens with convex surfaces on both sides, the third lens 13 is a negative lens between both surfaces, and the fourth lens 14 is an optical lens. It is constituted by a lens system in which the side bonding surface has a positive curvature toward the object side, and the focal length of the first lens group is F1, the focal length of the second lens group is F2. The composite focal length on the wide-angle side is Fw,
The composite focal length on the long focal length side is Ft, and the fourth lens in the second lens group
The radius of curvature of the bonding surface on the image side of the lens is RL4. If the combined focal length of the first lens and second lens in the second lens group is Ff, then Ff 0.45≦□≦0.7...■RL
4>0...It is characterized by satisfying the condition (■).

Generally, in a two-group zoom lens, the properties of the lens are greatly affected by the settings of the refractive powers of the first lens group and the second lens group. In particular, the setting of the refractive power of the lens group greatly affects the amount of peripheral light at the wide-angle end, the size of the front lens, and the operability during zooming.

Since it is possible to increase the zoom ratio to about 2.5 times based on such conditions, the above-mentioned conditional expressions 〇 to 〇 are required as basic conditions.

When condition (2) is below the lower limit, the refractive power of the first lens group becomes weaker, making it possible to correct aberrations in width, but the amount of movement of the first lens group due to zooming becomes large, resulting in a decrease in operability. Also, since the incident position moves toward the image side with respect to the lens group, the amount of peripheral light decreases, or the outer diameter of the lens in the lens group must be increased, making it more compact.
This is not preferable for cost reduction, etc.

Furthermore, when the upper limit of conditional expression (0) is exceeded, it becomes difficult to correct aberrations.

Therefore, the conditional expression (2) described above is required at the minimum.

On the other hand, conditional expression (2) indicates that the lens 11 in the second lens group,
This is to limit the ratio of the composite focal length of the second lens 12 and the composite focal length of the second lens group, and by satisfying the first conditional expression (■), the zoom ratio can be expanded while the second lens group and the second lens group at the far end of g4. It is possible to ensure the distance between the two lens groups and the distance between the apertures, and to correct aberrations.

When the fourth lens 14 in the second lens group is composed of a bonded positive lens, the above conditional expression 〇 must be satisfied, and the refractive index on the object side of the bonded surface of the fourth lens 14 must be Let n41 be the refractive index on the image side of the bonding surface of the fourth lens 14 as n42.

0.1≦∩41−n42≦0.41 −,,■
must satisfy the following conditions.

1- Set an appropriate difference in refractive index for the fourth lens system within the range of conditional expression 〇 described above, and also ensure that the radius of curvature of the bonded surface and the focal length of the second lens group are balanced by conditional expression 〇. can get.

Therefore, according to the 5 conditional expressions (Φ, 2), if glass with a high refractive index is used for the bonded convex lens and the bonded surface is given negative refractive power, the Petzval sum can be corrected.

Moreover, according to the fifth conditional expression (5), the fourth lens 14 has a positive curvature on the object side.

This makes it possible to correct field curvature on the wide-angle side.

Furthermore, when the fourth lens 14 of the second lens group is composed of three lenses for aberration correction, each lens has a biconvex positive lens, a biconvex positive lens, and a biconvex positive lens from the object side to the image side. a fourth lens 1 in the second lens group;
The radius of curvature of the bonding surface on the most image side of No. 4 is RL4. The refractive indexes of the three lenses constituting the fourth lens 14 are arranged in order from the object side to the image side: n41, ∩42. If it is r143, it is necessary to satisfy the following conditions.

When the second lens 12 in the second lens group is composed of a positive meniscus lens, the second lens 12 in the second lens group
The on-axis spacing of dL2. Second lens 12 in the second lens group
The axis from the most image side to the most object side of the third lens 13 -
When the L interval is dL2' and the h+i refractive index of the glass constituting the second lens 12 in the second lens group is ∩L2, the following conditional expression must be satisfied.

In the second lens group, the most object side surface of the second lens 12 has a strong positive curvature toward the object side, so that the aberration balance due to zooming can be corrected. Therefore, in order to ensure the distance between the lens group and the second lens group, there is a limit to the surface on which the principal point of the second lens group can be moved toward the object side. In order to control, dL2 is within the range that satisfies the conditional expression (■) mentioned above.
．． A means for changing dL2' is required, and the conditional expression (Φ) exists as one stage of this.

In the conditional expression 〇 described in , if the upper limit is exceeded, it is easy to move the principal point toward the object side, but the coma flare of the lower ray on the long focal length side, the color coma of the lower ray on the wide-angle side, The Petzval sum worsens.

On the other hand, when conditional expression 〇 becomes less than the lower limit, it becomes difficult to move the principal point position.

Because of the addition of J, it is necessary to satisfy conditional expression 〇.

Furthermore, when the second lens in the second lens group is composed of a cemented meniscus lens, the refractive index on the object side of the cemented lens constituting the second lens 12 is set to n21. The refractive index on the image side is n
22. The axial distance between the second lenses in the second lens group is d2.
If the axial distance from the most image side surface of the second lens 12 of the second lens group to the most object side surface of the third lens 13 is dL2', and the uniform refractive index of the glass constituting the second lens 12 is ∩L2°, then , n21≦n22...The following condition must be satisfied.

If the curvature of the cemented surface of the second lens 12 in the second lens 1T is negative toward the object side, and the conditional expression 〇 written in L, [phase] is satisfied, the second lens 12 in the second lens group becomes a meniscus monoton. Better aberration correction than in the case of a lens becomes +i (ability).

Specific examples of the present invention will be described below. However, in each example, f is the combined focal length of the entire lens system, F is the F number, Fl and F2 are the respective focal lengths of the lens group and the second lens group, R is the radius of curvature of each lens, and d is the axis The upper distance or the thickness of each lens, n is the d-line refractive index, ν is the Abbe number of the glass used for each lens, Po is the back focus, and R, d, n, ν are the values from the object side to the image side. The numbers are listed in order.

Example 1 f 28.85-87.9/3.8-4.9F1=-
49,00F2=38.80 R+=89.88 cl=4.45
n+=1.82280 p+=57.06R2
= 3000.00 d2= 0.20R:l
= 12E1.61 ch = 1.40
n3=1.77250 ν3=49.88
R4 = 22.57 cL = 8.80R
5 = 285.50 ds = 1.20
ns = 1.71300 ys = 53.8
4Rh = 33.29 db = 3.7
0Rr=32. +5 cl = 4.8
On+ = 1.69895 yr = 30.12
Ra= 143.20 d++= Variable Rq
= 48.10 dq = 3.45
nq =1.82280 yq =57.0
SR+o=-91,90d+o=0.20R++
= 19.3 fl d++ = 8.50
n++=1.82280 yu=57.08R
12= 57.45 cl+2= 1.09
RI3=-234,12d+3=5.00 n1
3=1.80518 ν13=25.43R+a=
17.9? du= 3.00R+s=
54.58 cls=1. oOn+5=1.
74320 Fl5=49.30R16=
22.85 d+6=5.15 n+6=
1.58732 Fl6=42.83R++=
-31,81 Zoom data Fw=28.85 Ft=87.9
F1=-49,0F2=38.8F f=23.29 ∩L2=1.8228 dL2=8.5
dL2'=1.09RL4=22.85 n
41=1.7432 n42=1.56732 Example 2 f 28.84-87.55/2.88-4.41F
l=-49,00F2=38.80 R+=88.77 dI=4.45
n+=1.58913 y+=60.97R
2=808.91ch=0.20R3
= 110.70 d3= 1.40
n3=1.80810 ν3=40.95R
a = 22.85 da = 7.83f
b=-288,87d5=1.20n
s = 1.72918 v5 = 54.88Rh
-42,29d6=3.40 Rt-38,89dt=4.85 n+=1.7
2B25 y+=28.46Re=14
25.39 ds = variable Rq = 4
7.47 dq = 3.15 nq =
1.69880 yq =55.52R+o=
-170,71d+o= 1.90RH= 22
．． 30 du = 7.40 n++ = 1.
89350 y 11=53.23R12=
57.45 d+2= 1.13R port=-
258,23d13=5.5On+3=1.80518
7+3=25.43RI4=19.35
du=2.80R15=42.14
d+s=1.00 n+s=1.806
10 y+5=40.95R16=20.
92 d+6=5.0On+6=1.58287
Si16=46.33Rat=-33,7
4 Zoom data Fw=28.84 Ft=67.55
Fl--49,00F2=38.8F f =25.
64 ∩L2 = 1.8935 dL2 = 7.40
dL2'=1.13RL4=20.92n
41=1.8081 n42=1.5828? Example 3 f 28.85-87.80/3.8-4.84Fl
=-48,70F2=38.14 R+ = 95.25 d+ = 4.70 Mountain=1.51880 ν, =84.15R2=
0.00 dz = 0.20R3 = 10
5.15 ch = 1.30 n3=1
．． 70154 ν3 =41.24Ra =
20.54 ds = 8.72 Rs =
-155,00ds = 1.15ns
=1.83854ys =55.38R13
= -154,18d+3=5.18 n+:
+=1.78442 y+3-25.71R1
6= 21.27 d+6= 4.75
n+6=1.54072 Fl6=47.
2ORat = -28,89 Zoom data Fw = 28.84 Ft = 87.55
Fl=-48, 70F2=38.14Ff=22.1
4 ∩L2 = 1.8?00 dL2 = 8,78
dL2°=0.75RL4=21.27n
41=1.79952 n42=1.54072 Example 4 f 2B, 84-87.55/3.8-4.85F1
=-44,83F2=35.08 Zoom data RL4=20.41 n41=1.79952
n42=1.54072 Example 5 f 28.85-87.55/3. [10-4,85
Fl=-45, 10F2=35.00 Zoom data RL4=18.83 n41=1.72000
n42=1.48749 Example 6 f 28.90-87.55/3.80-4.65F
1=-44,91F2=35.82 Rh=85.38 d6=2.10R
+= 38.70 dy=4.30 0
I=1.78472 y+=25.88R4o
= -87,13do+=0.20Rh=19.
85 d++=6.75 n++=1.898
80 yu=55.52R12=48.45
d+2=1.05R16=-29,50
d+6=0.15 Zoom data Fw=28.85 Ft=87.55
F1=-44,91F2=35.82F f=21
．． 9111 ∩L2 = 1.8988 dL2 = 8.75
dL2'=1.05RL4=23.22 n4
1=1.48749 n42=1.71195
n43=1.8845 Example 7 f 3B, 05-67.55/3.5-4.85F1
=-58,00F2=36.1 Zoom data RL4=22.48 n41=1.788
n42=1. ff0342 (Effects of the Invention) In short, the present invention uses the above-described configuration to increase the zoom ratio from 2 times to 2.5 times compared to the conventional zoom ratio while reducing fluctuations in aberrations, and reduces the overall length for compactness. The design is now as elegant as the conventional 2x zoom lens.Furthermore, by increasing the zoom ratio to about 2x with the configuration of the present invention, it is possible to design a compact 2-group zoom lens that has not existed in the past. , it has high practical value.

[Brief explanation of drawings]

Figures 1 and 2 are the configuration diagram and aberration diagram of the zoom lens of Example 1, Figures 3 and 4 are the configuration diagram and aberration diagram of the zoom lens of Example 2, and Figures 5 and 6 are The configuration diagram and aberration diagram of the zoom lens of Example 3, FIGS. 7 and 8 are the configuration diagram and aberration diagram of the zoom lens of Example 4, and FIGS. 9 and 10 are the configuration of the zoom lens of Example 5. 11 and 12 are block diagrams and aberration diagrams of the zoom lens of Example 6, and FIGS. 13 and 14 are block diagrams and aberration diagrams of the zoom lens of Example 7. Agent Patent Attorney Fuku 1) Ken Miwa, Group 1 -
■Techo 1- Tobdo No./7/〉〉゛°group 2nd Ln large stone mo No. 13
figure

Claims (1)

[Claims] (1) A first lens having negative refractive power from the object side to the image side.
A two-group zoom lens comprising a lens group and a second lens group having positive refractive power, and zooming is performed by changing an axial distance between the first lens group and the second lens group. One lens group is composed of a lens system in which a plurality of lenses having positive or negative refractive power are arranged in parallel,
The second lens group includes, in order from the object side to the image side, a first lens with positive refractive power, a second lens with positive refractive power, a third lens with negative refractive power, and a fourth lens with positive refractive power. The first lens in the second lens group is a positive lens with convex surfaces on both sides, the third lens is a negative lens with concave surfaces on both sides, and the fourth lens has a positive bonding surface on the image side facing the object side. It is composed of a lens system with a curvature, and the focal length of the first lens group is F1,
The focal length of the second lens group is F2, the composite focal length on the wide-angle side is Fw, the composite focal length on the long focal length side is Ft, and the radius of curvature of the bonded surface of the fourth lens in the second lens group on the image side is R.L.
4. If the combined focal length of the first and second lenses in the second lens group is Ff, then 0.35≦[Ft×Fw]/
[|F1|×(Ft+Fw)]≦0.50.45≦(F
A two-group zoom lens that satisfies the following conditions: f/F2)≦0.7 RL4>0. (2) The fourth lens in the second lens group is composed of a bonded lens having a positive curvature on the object side, and the refractive index of the bonded surface of the fourth lens on the object side is ∩41, and the fourth lens has a positive curvature on the object side. If the refractive index on the image side of the bonded surface is ∩42, then 0.1≦∩41−∩42≦0.41 RL4×∩42 0.38≦(RL4×∩42)/(∩41×F2)≦ 0
．． 6. A two-group zoom lens according to claim 1, wherein the two-group zoom lens satisfies condition 6. (3) The fourth lens in the second lens group is composed of three lenses, each lens being a biconvex positive lens, a negative lens, and a biconvex positive lens from the object side to the image side, The radius of curvature of the bonding surface on the image side of the fourth lens in the second lens group is RL4, and the refractive index of the three lenses constituting the fourth lens is ∩41 in order from the object side to the image side. ∩42
, ∩43, then ∩42>(∩41+∩43)/2 0.45<(RL4×∩43)/(∩42×F2)<0
．． 7. A two-group zoom lens according to claim 1, wherein the two-group zoom lens satisfies condition 7. (4) The second lens in the second lens group is a positive meniscus lens with a strong positive curvature on the object side, and the axial distance of the second lens in the second lens group is dL2, If the axial distance from the most image side of the second lens to the most object side of the third lens is dL2', and the refractive index of the glass constituting the second lens in the second lens group is ∩L2, then 0.07F2 ≦(dL2/∩L2)+dL2'≦0.1
A two-group zoom lens according to claim (2) or (3), characterized in that it satisfies the condition of 8F2. (5) The second lens in the second lens group is a positive meniscus lens that has a bonded surface with a positive curvature on the image side, and the most object side surface has a positive curvature on the object side, and The refractive index on the object side of the bonded lens constituting the second lens in the lens group is ∩21, the refractive index on the image side is ∩22, the axial spacing of the second lens in the second lens group is dL2, and the second lens is ∩21. If the axial distance from the most image side of the second lens in the lens group to the most object side of the third lens is dL2', and the average refractive index of the glass constituting the second lens is ∩L2', then ∩21≦∩ 22 0.07F2≦(dL2/∩L2')+dL2'≦0.
Claim 2 (2) or (3), characterized in that the condition of 18F2 is satisfied.
Group zoom lens.