JPS59229516A - Wide-angle lens - Google Patents

Abstract

PURPOSE:To obtain a bright wide-angle lens which has various aberrations compensated excellently by providing four convex, concave, convex, and negative meniscus lens groups successively from an object side and allowing this lens system to meet specific requirements, and inserting a plastic lens which has specific focal length between lens groups. CONSTITUTION:The lens system consisting of the four lens groups satisfy inequalities I -III, where (f), f123, and f4 are the focal length of the whole system, composite focal length of the 1st - the 3rd lens groups, and the focal length of the 4th lens group, and D6 is the gap between the 3rd and the 4th lens groups. Further, the plastic lens which has an aspheric surface as at least one surface is inserted in between lens groups of the lens system (i.e. between the 1st and the 2nd, the 2nd and the 3rd, or the 3rd and the 4th lens groups). The focal length fA of the plastic lens is specified as shown by an inequality IV.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Field of Application) The present invention relates to the BJ3ti wide-angle photographic lens, particularly a wide-angle lens using an aspherical surface with a small screen size.

(Prior art) A wide-angle lens with an angle of view of about 57 degrees and a brightness of F' 2.8 degrees, which can be used as an optical system for relatively small screen sizes such as disk cameras and facsimiles, has a small focal length. In recent years, no consideration was given to making the camera compact, and lenses with a large distance ratio were often used.However, by making the glass member aspherical for disc camera lenses, the telephoto ratio was reduced and various aberrations were reduced. Even after correction, O appeared. Also, υ using plastic lenses with refractive power has also appeared.

However, making the glass aspherical requires a complicated process, and if the plastic lens has refractive power, the optical system will become hot! Since it is susceptible to the influence of t@ damping, if the focal length digit is not one that makes a cohesive lens *i)Ij like a single-lens reflex camera, it becomes intermittent.

(Object of the invention) This b [, bright is the so-called wide telephoto a with a small zoom ratio
! ! By forming a re-lens thread with a glass lens, inserting a non-electrical glass lens with small refractive power into the glass lens 4, and making its surface aspherical! The objective is to provide a bright, wide-angle telephoto lens with small shadows and well-corrected distortion due to its aspherical surface. (Structure of the Invention) Lens system t= Lb'q41 diagram, Figure 2, Figure 3
As shown in the figure, the basic configuration consists of the first lens group, which is a convex lens with a strongly convex surface facing toward the object side, the second lens group, which is a concave lens with a strongly concave surface facing toward the opposite side, and It consists of the third lens group, which is a convex lens, and the l1I4 lens group, which is a negative meniscus lens with a strongly concave surface facing the object side. Focal length f4: tlz Focal length of 4 lens groups D6: 1, 3 / f <'/fe2s< 1.6 / when the distance between the 3rd lens detail and the 4th lens group is υ
f ・・・・・・(1)x, 0/f <1/Hf
41 <1.4/V ・・・・・・(2) 0, 2 O
f < Db < 0.32 f...
・(a lens system that satisfies at, and there is no space between each lens group of the above lens system, that is, between the 2nd lens group and the 2nd lens group, or between the 2nd lens group and the 3rd lens group) A plastic lens with at least one surface aspherical is inserted between the groups or between the third lens group and the fourth lens group, and the focal length Hf of the plastic lens is
1 person/<0.05/f...
・(4) FAL ◎ This lens system has a so-called telephoto type lens configuration with the 1st, 2nd and 3rd groups forming the front group and the 4th group forming the rear group. By setting the telephoto ratio to an unusually small value of about 1.2,
Moreover, the II aberration is made small given by this basic configuration. The conditions for this are clauses f'F(1) to 3).

If the lower limit of M f't' (1) is set to ζ, the telephoto ratio is large and the lens system is large, and vI! However, the bay surface is over-corrected. On the other hand, if the upper limit is exceeded, lens system #i becomes compact, but spherical aberration becomes insufficiently corrected.

In addition, strong pincushion distortion occurs.

Condition (2) relates to the fourth lens, and when the lower limit is exceeded, the curvature of the surface of the lens with a large telephoto ratio will be overcorrected.

On the other hand, if the upper limit is exceeded, the edge surface curvature will be insufficiently corrected, coma flare, and pincushion 1! type distortion aberration occurs.

Article f! 4: If the lower limit of (3) is exceeded, the surface curvature is insufficiently corrected, and the telephoto ratio becomes large, resulting in a large lens system. Conversely, if the upper limit is exceeded, spherical aberration will be insufficiently corrected. or,
It is necessary to increase the outer diameter of the fourth lens, which causes disadvantages in manufacturing.

Condition (4) relates to aspherical plastic, which is a feature of the present invention. As mentioned above, in the lens system of this invention, a plastic lens with weak refractive power is inserted into one of the four lens groups mentioned above.Plastic lenses can be relatively easily molded into aspherical shapes, and have not been put to practical use. However, it is easily affected by temperature and humidity, causing changes in the refractive index and expansion and contraction of half a cup of curvature, and has the disadvantage of being vulnerable to environmental changes.To avoid this, the refractive power of the plastic lens must be reduced. Therefore, the condition (4) is to almost eliminate the effects of environmental changes.By making the plastic lens at the mouth aspherical, it can be useful for correcting various aberrations. Forging is also effective when used to reduce coma flare at the outer edge points of the shaft.

Example 1ti An example in which a plastic lens is inserted between the 1st lens group and the 2nd lens group is shown.

/=100 7B-30,602F28.361122
, No. 70.311/4-8L425 fA-■ 176-2 B, 64"a4(0,1f)ll11-0.227X1G-1 In this implementation, the second lens group is a meniscus lens with negative refractive power. This makes it possible to reduce f123 even if the radius of curvature of the positive lenses on the sides of the first and third lenses is large enough.However, with this alone, various aberrations are insufficiently corrected at υ, which is aspherical. is designed to have negative lens motion.

When assuming an aspherical shape, C*-〇 +2 A (p i == 2) represents a reference spherical surface, and k is a quadratic surface coefficient.

And, if the plastic lens is between the third lens ridge and the 142nd lens υ like this actual 1 mN, it is desirable that it be within the range of △ Δ = he - ”” (0,1,f)yu(1
,0X10,"'(5)f" If the lower limit of this condition is exceeded, spherical aberration will not be under-corrected and overcoma flare will occur. Conversely, when the upper limit is exceeded, undercoma flare occurs and spherical aberration becomes overcorrected.

A second example shows a Leri in which an aspherical plus lens is inserted between the ll52 lens group and the third lens group.

Example 2 -1,184651J+00 AI==5.920551>-07pi=4.
OQOOA2w-1,67236Ll-(18P2=5
．． 000OA3m-1, 11304Ll-10pa=e
, ooo.

A4=-4,26087Ll-13P4=7.0000
For A5-IJ1003L)-15F5-a, 0000A
6==-3,61895Ll-18P6=9.0000
Mu7--9.393611J-21P7=10.000
0/=100 /Bw=aO,513(ss-28
, 1f, 23-as, 5as f4 depth - 82,901 fA - 0,546XlO' L16-26.00 MuX (0,115/% - 0,597 When it exceeds a desirable upper limit, undercoma flare increases, and when it exceeds a lower limit, overcoma flare becomes noticeable.

A third embodiment shows a target in which an aspherical plastic lens is inserted between the third lens group and the fourth lens group.

Example--1,424421J+00 Al--6,58109Ll-07Pi-4,000O
A2=-1,155151J-08P2=5.0000
A3=7. (i9043υ−101'3=6.00
00A4=4.261021J-12P4=7.00
00A5 engineering 1.575571J-14ps=s,oo
o.

A6= 4゜929191J-17P6=9.0OOOO
A72 1.412261J-19P7-10.000
0j''=100 fB=31.596 -28.
3゜f123 = 66.365 f4 = 7L7 (16 fA = 0.852 It is preferable that ΔX be in the following range. If the upper limit is exceeded, overcoma flare will be noticeable, and if the lower limit is exceeded, undercoma flare will occur.

The reason why the absolute value is given in the conditional expressions (5) (6 and 7) above is because the sign is reversed when the aspheric surface of the plastic lens is placed on the opposite side from each 5A embodiment.

(Effects of the Invention) Despite being a bright wide-angle lens as described above, the present invention has a small telephoto ratio of about 1.2, and as shown in the aberration diagram, each fJI aberration is corrected in a well-balanced manner.

Furthermore, the aspherical surface is a plastic lens surface with almost no refractive power; it is not only easy to mold, but also has the effect of being extremely little affected by the humidity environment.

[Brief explanation of drawings]

Figures 1, 2, and 3 are the first and second figures of this invention, respectively.
The lens sectional views of the second and third f11i1 examples, and FIGS. 4, 5, and 6 are aberration diagrams in the first, second, and third implementation directions, respectively. Tokken Applicant Roku Konishi Photography Eimi Ni Company Applicant Agent Patent Attorney Fumi Sato (and 1 other person) 5th mouth F2.8 Spherical coverage, )= Fig. 6 F2.8 Spherical surface + 1 maX・ω =28.3 JII C aberration 1μ Distortion aberration non-1 degree aberration
distortion aberration

Claims (1)

[Claims] The first lens group is a convex lens with a strongly convex surface facing the object side, and the second lens group is a concave lens with a concave surface facing the lens group.
Lens groups, 3rd lens group which is a convex lens and 4th lens group which is a negative meniscus lens with a strongly concave surface facing the object side, f: Focal length of the entire system f123: 3rd lens from the 3rd lens group Synthetic focal length to the group f4: Focal length of the fourth lens group D6: Distance between the third lens ridge and the fourth lens group: 1.3/f < /f, 23 < 1.6/V1.0 /f
< /If41 <1.4/V0.2Of (
A lens system that satisfies a6<0.32f, wherein one lens between each lens group of the above lens system, that is, between the first lens group and the second lens group, or between the second lens group and the third lens group. A plastic lens with at least one surface aspherical is inserted between the lens groups or between the third lens group and the fourth lens group, and the focal length of the plastic lens is l1rIIf.
1/17 AI < 0.05/f is the % enemy of Hiroto lens