JPS6055311A - Zoom lens - Google Patents

Abstract

PURPOSE:To constitute a zoom lens of eight-element constitution which has an about 4 F number and an about 3X zoom ratio while including a 28mm. wide angle as a lens for a 35mm. single-lens reflex camera at low cost. CONSTITUTION:The lens system consists of the 1st and the 2nd lens groups successively from an object side, and the air gap between those two lens groups is varied to perform variable power. Said 1st lens group consists of the 1st positive lens, the 2nd negative meniscus lens having a convex surface on the subject side, the 3rd negative lens, and the 4th positive lens successively from the object side, and has negative refracting power on the whole. The 2nd lens group consists of the 5th positive lens, the 6th positive meniscus lens having a convex surface on the object side, the 7th negative lens, and the 8th positive lens and has positive refracting power on the whole. Those two lens groups satisfy inequalities.

Description

[Detailed description of the invention]

The present invention relates to a zoom lens having an F number of about 4 and a zoom ratio of about 3 times including a wide angle of 28 mm as a lens for a 35 mm format eye reflex camera, and in particular, it is provided at low cost by reducing the number of constituent elements. related to a zoom lens designed to First, to describe the configuration of the present invention, in order from the object side, there is a positive lens, a second lens, a negative meniscus second lens with a convex surface facing the object side, a negative third lens, and a positive lens, a first lens. a 5th lens which is a positive lens; and a 6th lens which is a positive meniscus lens with a convex surface facing the object side;
It consists of a 7th lens that is a negative lens and an 8th lens that is a positive lens, and has a positive refractive power as a whole, and the air distance between the 7th lens group and the 2nd lens group is changed. This is a zoom lens characterized in that it performs magnification change by and satisfies the following conditions. (1) 1.5<l f r I/ f w<2.0
, f x < 0 (2) 6.0 < f 1 / f
w<12.0(3) (n 2 + n 3 ) /2>
1.72 (4) n a >1.75 (5) 0.04< d s / f w <0.15
(6) 0.75<fs, e/fw<1.
0(7) 1.60<(ns +ns)/
2<1.75(8) 1.2<R9/ f w<2.0
(9) 0.7<If71/fw<0.85, fl<
0(10) n, >1.70 (11) 1.50<Rxs/fw<-0,80fw:
Shortest focal length in the entire system f□: Focal length of the lens group fl: Focal length of the lens f5+6: Combined focal length of the 5th and 6th lenses fl: Focal length of the 7th lens nl: Used for the i-th lens Refractive index d6 of the glass material: Air distance R9 between the third and fourth lenses: Radius of curvature of the object side surface of the fifth lens R16: Radius of curvature of the image side surface of the eighth lens By satisfying the above-mentioned conditions, the present invention has achieved a configuration of only 8 sheets and approximately 3 sheets.
A major feature is that a zoom lens with a double zoom ratio can be realized with excellent performance. Next, each of the above conditions will be explained. Condition (1) relates to the refractive power of the first lens group. This condition (
If the lower limit of 1) is exceeded, the refractive power of the 1st lens group becomes too strong, causing overcorrected spherical aberration and astigmatism, making it difficult to maintain good optical performance. Also, the condition (
If the upper limit of 1) is exceeded, the refractive power of the lens group becomes too weak, and - it becomes impossible to secure the back focus required for an eye reflex camera lens, or the total length of the lens becomes long in order to secure the back focus. There will be some drawbacks. Condition (2) relates to the refractive power of the first lun. The lens serves as a positive lens with weak refractive power and mainly contributes to correcting distortion on the short focal length side. If the lower limit of condition (2) is exceeded, the refractive power of the first lens becomes strong, which is effective in correcting distortion aberration, but undesirably causes chromatic aberration of magnification with respect to the beam of light that should be imaged at the periphery of the screen. On the contrary, the condition (2
), the lens' function as a lens is impaired and distortion cannot be corrected. Condition (3) relates to the refractive index of the glass materials used for the second lens and the third lens. Both the second lens and the third lens are negative lenses, and are the central elements in the first lens group having negative refractive power. If condition (3) is violated, the refractive action that must be borne by each lens surface of the second lens and the third lens becomes large, which is particularly undesirable because it causes overcorrected spherical aberration and astigmatism. In addition, the Petzval sum becomes too small, which is undesirable as it causes excessively corrected field curvature, especially on the long focal length side. Condition (4) relates to the refractive index of the glass material used for the fourth lens. The fourth lens is a positive lens that generates under-corrected spherical aberration and has the effect of canceling out over-corrected spherical aberration generated by the second and third lenses. However, if condition (4) is violated, the fourth lens The radius of curvature of each surface of the lens becomes tight, producing high-order aberrations, which undesirably reduces the contrast at the center of the screen, especially on the long focal length side. Condition (5) relates to the air gap between the third and fourth lenses, and together with conditions (3) and (4), it suppresses spherical aberration to a minimum, especially on the long focal length side, and secures the necessary back focus. This is a necessary condition for doing so. Condition (5
) If the lower limit of Therefore, a large amount of overcorrected spherical aberration occurs, which is undesirable. Moreover, when the upper limit of condition (5) is exceeded, the air gap widens and the second lens. In order to correct the over-corrected aberrations generated by the third lens, the first surface (r7) of the fourth lens becomes tight, which is undesirable because higher-order aberrations ultimately remain. Condition (6) relates to the combined refractive power of the fifth lens and the sixth lens. The fifth and sixth lenses have strong positive refractive power, contributing to the fact that the first lens group is a positive lens, and also correcting overcorrected spherical aberration and astigmatism that occur in the fifth lens. It also has the effect of bringing the principal point of the 1st lens group forward and making the entire lens system more compact. If the lower limit of condition (6) is exceeded, the combined refractive power of the fifth lens and the sixth lens becomes too strong, and the fifth lens becomes too strong. Each surface of the sixth lens becomes tight, which is undesirable because it causes too much undercorrected aberration. On the other hand, if the upper limit of condition (6) is exceeded, the composite refractive power will be weakened, resulting in a drawback that the total length of the lens will increase. Condition (7) relates to the refractive index of the glass material used for the fifth lens and the sixth lens. If the lower limit of condition (7) is exceeded, 5.
The radius of curvature of each surface of the sixth lens becomes tight, resulting in insufficient correction of spherical aberration and astigmatism, which is unfavorable in terms of performance. On the other hand, if the upper limit of condition (7) is exceeded, the Petzval sum becomes too small and excessively corrected field curvature occurs, particularly on the long focal length side, which is not preferable. Condition (8) concerns the radius of curvature of the object side surface of the fifth lens,
Together with the conditions (6) and (7), this is involved in controlling spherical aberration, especially on the long focal length side. conditions(
8) Even if the lower limit is exceeded or the upper limit is exceeded, the aberration correction balance of the fifth lens will be disrupted, and undercorrected spherical aberration will remain. Condition (9) relates to the refractive power of the seventh lens. The seventh lens is the only negative lens in the fifth lens group, and is involved in correcting all aberrations such as spherical aberration, dichromatic aberration, and astigmatism. Condition (9
), the refractive power of the seventh lens becomes too strong, resulting in overcorrected spherical aberration. Either the astigmatism remains or it becomes necessary to add an additional positive lens to the second lens group in order to correct the aberration. It misses the purpose. Furthermore, if the upper limit of condition (9) is exceeded, the refractive power of the seventh lens becomes too weak, and the fifth lens becomes too weak.
Condition (10) relates to the refractive power of the seventh lens, as the ability to correct 9 chromatic aberrations such as undercorrected spherical aberration and astigmatism occurring in other positive lens groups in the lens object is lost, resulting in performance problems. . Condition (1
0), each surface of the seventh lens becomes tight, and
The Petzval sum becomes too small, resulting in overcorrected field curvature, especially on the long focal length side, and high-order spherical aberrations remain, which is undesirable. Condition (11) relates to the radius of curvature of the image-side surface of the eighth lens, that is, the final lens, and is particularly related to correction of spherical aberration. When the lower limit of condition (11) is exceeded, the lens surface becomes loose;
In particular, the ability to correct spherical aberration is lost on the long focal length side. Conversely, if the upper limit of condition (11) is exceeded,
The radius of curvature of the lens surface becomes too tight, which is undesirable because undercorrected spherical aberration remains. Examples of the present invention will be described below. Here, r is the radius of curvature of each surface of the lens, d is the lens thickness or distance between lenses, 1 is the refractive index of each lens, and y is the Abbe number of each lens.

[Example IJ FNo. 1: 3.6-4.6 f = 28.9-7
7.5rdn. 1 222.238 4.06 1.62041. ,
60.32'-632.116 0.10 3 135.029 2.00 1.74400 44
．． 74 23.300 6.98 5 31.5.412 1.60 1.80610 4
0.96 40.600 3.48 7 36.71B 4.95 1.80518 25.
48 160.000 Variable 9 40.168 '4.44 1.72000 50
．． 310 -166.077 0', 10 11' 22.339 4.59 1.58913
61.012 80.500 1.16 13 -236.000 8.59 1.80518
25.414 18.982 2.17 15 120.600 3.09 1.60342 3
8.016 -36.718 1 f r I ”49.16=1.701-f Wf
1 = 265.52 = 9.219・f w (n 2
+ n 3 ), / 2 = 1.77505 n 4 =
1.80518 d 6 = 3.48 = 0.12 (l f wf '5
．． 6 =24.28=0.840・f w(n s +
n a ) /2 = 1.65457Rg = 40.1
68=1390・f wl f 7 + =21.50
=0.744・f w 7 ”1.80518 R+ 6 = 36.718” 1.271-f W [
Example 2 FMO1: 3.6-4.6 f = 28.9-77.
5rd n. 1 239.598 3.74 1.65830 57
．． 32 -618.955 0.10 3 116.304 2.00 1.83400 37
．． 24 23.780 9.16 5 412.722 1.60 1.79952 42
．． 26 4B, 455 2.12 7 38.135 4.26 1.84666 23.
98 170.176 Variable 9 52.131 3.70 1.73400 51.
510 -99.505 0.10 11 23.810 4.04 1.65100 56
．． 212 6C3132,69 13-146,4878,481,8051825,4
1421,3722,44 15228,3823,031,5407247,21
6-28,869 1f 11 =52.83 =1828・f wf ,
=262.85=9.095- f w(n 2 +
n3)/2=1.81676n4=1.8
4666 d 6 =2.12=0.073・f wf 5 . 6
=25.59=0.885- f w(n s +
n 6) /2=1.69250Rg=52.131
=1.804− f wI f 7 + =22.65
=0.784・f wrI7 −1.80518 R,6=−28,869= −0,999・f w

[Brief explanation of the drawing]

Figure 1 is a lens diagram of Example 1, Figures 2 and 3 are aberration diagrams of Example 1 at the end focus side and long focal point side, respectively, Figure 4 is a lens diagram of Example 2, and Figure 5. , and FIG. 6 are aberration diagrams on the short focus side and long focus side of Example 2, respectively. vj j Figure 2 Figure 2 Sine condition Figure 3 Stop string condition No. 6 Figure 1 70 = Distortion aberration

Claims (1)

[Claims] In order from the object side, a positive lens, a second lens, a negative meniscus lens with a convex surface facing the object, a negative third lens, and a positive fourth lens. a first lens group having negative refractive power as a whole; a fifth lens that is a positive lens; a sixth lens that is a positive meniscus lens with a convex surface facing the object side; a seventh lens that is a negative lens; and a positive lens. 8th lens, and a 2nd lens group having positive refractive power as a whole.
A zoom lens that performs magnification by changing the air spacing between lens groups and satisfies the following conditions. (1) 1.5<lf■1/fw<2.0, f+<0
(2) 6.0< f 1/ f w < 12.0 (3)
(n 2 + n 3 ) / 2 > 1.72 (4)
n a > 1.75 (5) 0.04 < d 6/ f w < 0.15 (6
) 0.75<fS, s/fw<1.0
(7) 1.60<(ns+n6)/2<
1.75(8) 1.2<R9/ f w<2.0(9
)0.7(lf7+/fW<0.85, fl<0(
10) n? >1.70 (11) -1,50<Rs s/f w<-0,
80fw: Shortest focal length in the entire system f■ = Focal length of the 1st lens group fl: Focal length of the 1st lens f5. e: combined focal length fl of the fifth lens and the sixth lens; focal length ni of the seventh lens: refractive index of the glass material used for the i-th lens d6: air distance between the third lens and the fourth lens R9: the fifth lens Radius of curvature R16 of the object-side surface of the lens: Radius of curvature of the image-side surface of the 8th lens