JPS61267720A - Triplet lens having rear diaphragm - Google Patents

Abstract

PURPOSE:To obtain a superior wide angle lens having a short back focus by arranging a positive meniscus lens having a specific focal distance and turning its convex surface to the object side, a negative single lens having concave surfaces on both the sides and a positive lens having convex surfaces on both the sides successively from the object side with specific intervals each other. CONSTITUTION:The positive meniscus lens turning its convex surface to the object side, the negative lens having concave surfaces on both the sides and the positive lens having convex surfaces on both the sides are arranged successively from the object side with slight air intervals, a diaphragm is arranged adjacently on the back of these lenses and conditions such as (1) 0.135<D1/f<0.18, (2) 0.65<f1/f<1.30, (3) 0.33<f3/f<0.5 [f: the focal distance of the whole system, fi the focal distance of the i-th lens and Di: an interval between the i-th surface and the (i+1)th surface] are satisfied. In such a lens, its back focus can be shortened without increasing the refractive force of the 1st lens so much and a distance between the front surface of the lens and the image surface is extremely short to form compact constitution. Although the lens is a wide angle lens having 32 deg. half picture angle, respective aberrations are effectively corrected and the influence of a production error is suppressed at a low degree.

Description

[Detailed Description of the Invention] Purpose of the Invention (Field of Industrial Application) This invention is directed to a triplet lens with a vk aperture, especially an f! This relates to a lens with a short back focus of 4.

(Prior Art) In recent years, with the miniaturization of lens-shutter cameras, there has been an increasing demand for thin photographic lenses, and telephoto type wide-angle lenses have been developed. Although the total thickness of these lenses from the front surface of the lens to the film surface can be made very short, the lens shape itself tends to be somewhat large in both length and size. Another problem is that the manufacturing cost of the lens is relatively high.

In order to avoid these difficulties, small lenses with a behind-the-scene aperture are being reconsidered.

Among this type of lenses, the triplet lens has a structure with a simple iris.
No. 0-2807 and the like are known. However, the angle of view of these is only about 27 degrees, which is small for a compact camera. JP-A-57-2012 is the same application as this application, and is a wide-angle lens with an angle of view of 32 Fc. Although it had a compact structure, the third lens had a large refractive power and was susceptible to manufacturing errors.

In addition, although the refractive power of the Ili@3 lens disclosed in JP-A-59-160118 is smaller than that of the above lens, the refractive power of the first lens is extremely strong, and it is also susceptible to manufacturing errors. ing. Also, the coma flare is large. Furthermore, JP-A-59-11'10119;
No. 160120 and No. 59-34510 use aspherical surfaces, which tend to result in high costs.
Luns' refractive power has become stronger.

(Problems to be Solved by the Invention) In lenses with a simple structure such as a triplet, manufacturing errors often have a large effect on optical performance. Therefore, in simulation design, it is necessary to create a configuration that is less affected by manufacturing errors.

This invention has an angle of view of 30@ or more and an F number of 3.5.
The objective is to obtain a relatively wide-angle lens that is less affected by manufacturing errors and has a short back focus.

Structure of the Invention (Means for Solving the Problem) In this invention, C. The triplet lens consists of, in order from the object side, a positive meniscus lens with a convex surface facing the object side;
It has a configuration in which a negative biconcave single lens and a positive biconvex lens are arranged with a slight air distance from each other, and a diaphragm is arranged close behind them, 0.135 <D1/f <o , 1g...
...(1) 0.65 < fl /f < 1.3
0 ...... C) 0.33 <f5/
f <0.5 (3) where f: focal length of the entire system fi: focal length of the i-th lens Di: the distance between the first surface and the i+1 surface is satisfied.

Furthermore, in order to improve performance, 2.0X10-2 <'w <5.0X10-2
・------(4) 1.0X10-2 <D4. y
<4.5X10-2 ・・・・・・(5)6
．． 7X10-2 <L)5/de <1.5X 10-
' ・・・・・・Wholesale and secondary 0.27 <'1/f<0.39 ・-
・-(7)0.27 <'a/f <0.42
・・・・・・(8)0.40<'
S/f<0.95 ・−・・・・(9)−
0,7o <”6/f <-0,45-・-
(1(1)1.7 <N1, Ns
...-(11) 1.7 <N2
・・・－・・・(12) However, ri: *Curvature of the ivr-th surface from the body side half a frame Nl: the i-th
It is desirable that the refractive index of the lens be satisfied.

(Function) This invention attempts to obtain a lens system with a short back focus fB without increasing the refractive power of the first lens. Conditions (1) and (2) are for this purpose.

If the lower limit of condition (1) is exceeded, the refractive power of the first lens must be strong in order to shorten the back focus.
The influence of 11 differences is significant. Moreover, the perapal sum becomes large, and the edge surface curvature becomes insufficiently corrected. If the upper limit is exceeded, the spherical aberration will be insufficiently corrected, and the vignetting of the off-axis light beam will become large.

If the lower limit of condition (2) is exceeded, the decentering of the first lunion will increase the degree to which the aberrations deteriorate, and the coma fray occurring at the second lunion will increase. On the other hand, if the distance exceeds at-, the back focus cannot be shortened.

Condition (3) is a condition for reducing the degree of aberration deterioration when the third lens is decentered from the optical axis of the first and second lenses. As the focal length of the third lens becomes shorter beyond the lower limit, the eccentricity error increases. The upper limit indicates the limit at which the vignetting of the off-axis light beam becomes excessive. Condition (4), which causes overcorrection of field curvature, relates to the distance between the first lens and the second lens, and since this is a wide-angle lens, this distance particularly affects vignetting. When the upper limit is exceeded, the vignetting at the bottom of the off-axis light beam becomes large, and conversely, when the lower limit is exceeded, the vignetting at the top becomes large.

Condition (5) relates to the distance between the second lens and the third lens, and affects vignetting similarly to condition (4).

If the upper limit is exceeded, not only will vignetting increase, but spherical aberration will also be insufficiently corrected. On the other hand, if the lower limit is exceeded, there will be problems in holding the lens.

Condition (6) relates to the thickness of the third lens; when the upper limit is reached, the vignetting increases, but when it exceeds the lower limit, the extraverted coma increases.

Condition (7) relates to the radius of curvature of the object side surface of the second lens, and when the upper limit is exceeded, spherical aberration is insufficiently corrected, and when the lower limit is exceeded, the extroverted coma increases.

Condition (8) relates to the radius of curvature of the acid side surface of the second lens; exceeding the upper limit causes undercorrection of spherical aberration, and exceeding the lower limit causes overcorrection of field curvature.

Article f! f-(9) relates to the radius of curvature of the object side surface of the third lens; when the upper limit is reached, spherical aberration is insufficiently corrected, and when the lower limit is exceeded, pincushion distortion aberration increases.

Condition 00) relates to the radius of curvature of the image side surface of the third lens, and when the upper limit is exceeded, the field curvature will be undercorrected, and when the lower limit is exceeded, the spherical aberration will be overcorrected.

Condition (11) is a condition for increasing the refractive index of the 11th and 3rd lens and decreasing the perapard sum, and condition (12)
When the refractive index of the second lens becomes small beyond this value, the radius of curvature of the second lens becomes small and coma flare increases.

(Example) Examples will be shown below. Symbols in the table are in addition to those mentioned above, F is F number, ω is angle of view, FB is back focus,
ν indicates the Atsube number ◎ Example 1 f, = 85.04 f, = 36.72 f13 = 77.71 Example 2 6 -61.085 f, = 86.64 f5''-36,52 fB = 77 .68 Example 3 RD N ν 5 78586 8.89 1.83400
3726 -64.769 /1=72.14 f5=43.81 fB=77.65 Example 4 RDN ν f'l -66,077 f,=90.58 -f5=34.6 Nine=77.66 Effects of the Invention As seen in the examples, the lens of this invention can shorten the bank 7 orcus without increasing the refractive power of the first lens, and the image plane from the front of the lens is also short, making it compact and compact. I was able to use it as a lens. And the half angle of view is 3
Although it is a wide-angle lens with an angle of 2.2 mm, each aberration is well corrected, and the effects of manufacturing errors can be kept to a minimum.

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing the structure of the lens of the present invention, and FIGS.
FIG. 4 is an aberration curve diagram of an example, a third example, and a fourth example. Patent applicant: Konishiroku Photo Industry Co., Ltd. Patent agent
Patent Attorney Fumi Sato Male (1 person) Fig. 1 Fig. 2c81j F85 Density 2 = 31.5° Spherical aberration Astigmatism Distortion aberration Comatic aberration No. 3 Spherical aberration Astigmatism Distortion atu
ty difference calculation 4 Figure F3.5 Blowing 2 = 31.5° Spherical aberration Astigmatism Distortion aberration Single 5 Figure F3.5 Spherical LTL aberration Astigmatism 2 = 32 Distortion aberration

Claims (1)

[Claims] In order from the object side, a positive meniscus single lens with a convex surface facing the object side, a negative double-concave single lens, and a positive double-convex lens are arranged with a slight air distance from each other, and behind them 0.135<D_1/f<0.18 0.65<f_1/f<1.30 0.33<f_3/f<0.5 where f: total Focal length of the system f_i: Focal length of the i-th lens D_i: Triplet lens with a rear aperture that satisfies the condition for the distance between the i-th surface and the i+1 surface