JPS6046519A - Wide-angle attachment lens - Google Patents

Abstract

PURPOSE:To compensate various aberrations excellently by allowing a lens system consisting of a positive and a negative lens to meet specific requirements. CONSTITUTION:This attachment lens LA is attached at the object side of a zoom lens LZ having a macro-photography mechanism and has negative focal length nearly equal to the object distance at which photography is possible with the macro-photography mechanism. This attachment lens has the positive lens LP and negative lens LN. In this case, inequalities I -IV hold, where fp and fN, np and nN, and nup and nuN are the focal lengths, refractive indexes, and Abbe numbers of the positive lens LP and negative lens LN respectively and (f) is the focal length of the whole attachment lens LA.

Description

DETAILED DESCRIPTION OF THE INVENTION (Technical Field of the Invention) The present invention relates to an attachment lens that is attached to the object side of a zoom lens having an ultra-close-up shooting mechanism to achieve a wide angle.

(Background of the Invention) Conventionally, as a means of realizing a wide angle of zoom lens,
The afocal telescope consists of a negative lens group and a positive lens group in order from the object side, making up an inverted Galilean telescope system as a whole.
How to attach a front converter, and attach a negative lens with a focal length approximately equal to the object point distance while activating the super close-up shooting mechanism of the zoom lens body and focusing on an object point that is extremely close to the lens. A method (Japanese Unexamined Patent Publication No. 52-34726) is known. The former method allows extremely close-up photography in the entire zooming range, but the converter optical system becomes complicated and large. On the other hand, although the latter method has the disadvantage that zooming is not possible when the axotiment lens is attached, it has the advantage that the configuration of the attachment lens can be extremely simplified. However, as is conventionally known, if a 7-tasotient lens is constructed with only a negative single lens,
Various aberrations, especially curvature of field caused by deterioration of the besopar sum,
Also, it is not possible to sufficiently correct distortion and chromatic aberration.

(Objective of the Invention) An object of the present invention is to solve the above-mentioned drawbacks and provide an extremely high-performance wide-angle attachment lens.

(Summary of the Invention) The present invention constitutes an attachment lens with a positive lens and a negative lens, and finds optimal conditions for power distribution, refractive index, and Abbe number for both lenses.

Generally, when attaching a wide-angle attachment lens for a zoom lens such as the one of the present invention, it is often done in the macro shooting state of the zoom lens at its wide-angle end, where the object distance is the shortest. The width of the luminous flux becomes extremely small. Therefore, correction of spherical aberration and coma aberration is not a big problem. However, zoom lenses generally have a negative Petzval sum (
Wearing an Akufuchimen 1 lens that is located in the circa direction and has a negative power will further worsen the Petzval sum to a negative value,
This causes field curvature and astigmatism. Now, if the focal length of the attachment lens consisting of a single lens is f (<0), the refractive index is n, and the Petzval sum of the sum lens body is Pz, then the Bé-Nohar sum P of the entire lens system when the attachment lens is attached is P =I'Z+1/(n-f) (1). (
1) As is clear from the formula, in order to alleviate the deterioration of the Petzval sum, it is better to make the refractive index n as large as possible, but in a single lens, the value of n is about 1.8 at most, so the Petzval sum can be well corrected. It was difficult to do so.

In the present invention, an attachment lens having a focal length f (<0) has a focal length Mu f p, a refractive index np, and a number νp.
positive lenses t and p having focal length fN and refractive index nN
, and a negative lens LN with Atsube number νN, and by imposing the following conditions roughly: 1.2<f/fN<1.8 (2) np<nN (3) νp<rN (4) Solving the various shortcomings, I
This is a realization of a J-type TTL attachment lens. Since the positive lens Lp and the negative lens LN are arranged extremely close to each other compared to their focal lengths, they can be regarded as a thin, close-contact two-lens system. Therefore, if the apparent refractive index of the attachment lens is no and the apparent roughness is ν0, then 1/f=1/fN + 1/fρ (5) 1/(f
-no) -1/ (fN-nN)+1'/ (fp
-np) (6) 1/ (r・νo) = 1/ (rN・vN
)+1/(fp・νp) (7) holds true. Therefore, from equations (5) and (6), 1/no
= El (jN-nN) + (1-f/IN) ・1/np (8). (
From equation 8), if f, /fN>i, nN>np, the apparent refractive index no can be made larger than the refractive index of a single lens, and as a result, from equation (1), the Petzval sum for the entire system is can alleviate the deterioration of Moreover, n
The larger the difference between N and np, the more f/'fN
The larger the difference is, the larger the value of the apparent refractive index no of the attachment lens can be.

However, it is desirable to set the value of f/fN within the range of condition (2) described above. If the upper limit of condition (2) is exceeded, as is clear from equation (5), the powers of the positive lens Lp and negative lens LN will become too strong, and various aberrations will worsen. Moreover, if the lower limit of condition (2) is exceeded, the apparent refractive index is 1
The effect of reducing the value of 10 becomes small, and deterioration of the Petzval sum cannot be alleviated.

In the basic configuration of the present invention as described above, the positive lenses t, p, and the negative lens LN are further arranged in order from the object side.
p and negative lens LN in this order, and when the shape factors of each lens are xp and xN, -0,2<x p<2.0 (10) -s,0<x
It is desirable to set N <-1,0 (11). However, the shape factor do.

Generally, barrel-shaped distortion occurs at the wide-angle end of a zoom lens, and by attaching a lens with negative power, the distortion becomes even worse, but as mentioned above, placing a positive lens on the object side , by setting the shape factors of the two lenses within the range of formulas (10) and (11), distortion aberration is corrected, and at the same time, other aberrations, especially meridional curvature of field and zagital curvature of field, are well balanced. I can do small things.

Since the power becomes too strong, it is advantageous in correcting distortion, but astigmatism worsens. On the other hand, if the upper limit is exceeded, distortion cannot be corrected completely.

If the lower limit of condition (11) is exceeded, astigmatism worsens in the positive direction. If the upper limit is exceeded, astigmatism worsens in the negative direction, and distortion becomes too negative.

(Example) The example according to the present invention satisfies all of the above-mentioned conditions, and includes, in order from the object side, a positive lens Lp with a more strongly curved surface facing the object side, and a negative meniscus lens with a convex surface facing the object side. The lens LN has a hole.

The specifications of the first embodiment are as follows. However, it shall represent the order of.

(First example) rl=235.00 dl=8.0On1=1.57
502 vl =41.6r2--2751.08d
2=0.50r3=163.26 d3=2.50
n2=1.772801'2 =49.4r4=52
．． 89 f = -144,132 fp = 376.894 fN = -102,243 Focal hole Rf = 9.3-118.1, zoom ratio 12.6 for the wide-angle aquenchment lens L of the first embodiment
FIG. 1 shows a lens arrangement diagram when the lens is attached to a zoom lens LZ. This zoom lens was published in Japanese Patent Application Laid-Open No. 54-127.
This lens is based on the zoom lens disclosed in Japanese Patent No. 322. At its wide-angle end, this zoom lens
By moving the outstanding G42 of the relay system G4 by 0.6 mm toward the object, macro photography with an object distance Do = 160 mm is possible. In this macro shooting state, it is possible to attach the wide-angle attachment lens of the first embodiment of the present invention, and the combined focal length of the entire system is 6:7 mm, with a half angle of view of 41.
It will be 4 degrees. At this time, the distance between the acnotiment lens and the first surface of the zoom lens is 18.86.

The specifications of this zoom lens in the macro state are shown in the table below, and FIG. 2 shows various aberration diagrams in the wide-angle infinity photographing state using the wide-angle attachment lens of the first embodiment.

Next, the specifications of the second embodiment according to the present invention will be shown.

(Second example) rl=220.00 dl=5.00 n1=1.5
9507 ν1=35.1r2= 1727.14 d
2=0.50r3=80.00d3=1.90n
2=1.79668 v2 =45.5r4= 40.
23 f = -140,242 fp = 432.147 fN - -103,773 The wide-angle axotiment lens LA of the second embodiment has a focal length r = 9:s -123,5, and a zoom ratio of 13.0.
FIG. 3 shows a lens arrangement diagram when the lens is attached to the zoom lens LZ. This zoom lens has a negative lens group G4N and a positive lens group 6 in the third embodiment disclosed in IQM (Japanese Patent Application No. 57-97371) by the same applicant as the present application.
The positive lens group G4P of the rear group G42 of the relay lens system, which is divided into 4P and 4P, is moved 0.6 mm toward the object side to set the macro shooting state, and the object distance is 00 = 123 mm at the wide-angle end.
The camera enters macro photography mode. In this macro JIi&fg state, it is possible to attach the wide-angle aquenchment lens of the second embodiment of the present invention, and the combined focal length of the entire system is 7.0 +++ m, and the half angle of view is 39.4 degrees.

At this time, the distance between the axotiment lens and the first surface of the zoom lens is 15.98Q.

The specifications of this zoom lens in the macro state are shown in the table below.

1]1 FIG. 4 shows various aberration diagrams in a wide angle of view infinity photographing state when the wide-angle J Tasotimento lens of the second embodiment is attached to the zoom lens. In the various aberration diagrams shown in FIGS. 2 and 4, spherical aberration (Sph), astigmatism (ASt)
), distortion aberration (DiS), and coma aberration (Coma), and in the spherical aberration diagram, the amount of violation of the sine condition is also shown with a dotted line.

From each aberration diagram, it is clear that both the first and second embodiments suppress distortion and various aberrations are well corrected.

(Effects of the Invention) As described above, according to the present invention, the conventional drawback of insufficient performance due to insufficient correction of Petzval sum is solved,
It is possible to provide an extremely high-performance wide-angle attachment lens, which greatly contributes to expanding the photographic area while maintaining the excellent imaging performance of a zoom lens.

[Brief explanation of drawings]

Fig. 1 is a lens arrangement diagram of the first embodiment according to the present invention in a used state, Fig. 2 is a diagram of various aberrations in the state shown in Fig. 1, and Fig. 3 is a lens arrangement diagram of a second embodiment according to the present invention in a used state. figure,
FIG. 4 is a diagram of various aberrations in the state of FIG. 3. (Explanation of symbols of main parts) L8; Attachment lens Lp; Positive lens LN; Negative lens LZ; Zoom lens Applicant Nippon Kogaku Kogyo Co., Ltd. Agent Takao Watanabe"i2 Figure

Claims (1)

[Claims] (1) In an attachment lens that is attached to the object side of a zoom lens having an ultra-close-up photography mechanism and has a negative focal length approximately equal to the object distance that can be photographed by the ultra-close-up photography mechanism, The attachment lens has a positive lens and a negative lens, each of which has a focal length of fp+fN and a refractive index of np+.
nN, the Atsube number is 1 sill N, and the focal length of the attachment lens is f, then 1
．． A wide-angle attachment lens that satisfies the following conditions: 2<f/IN<1.8 np<nN νp×νN. 2. Arranging the positive lens and negative lens in order from the object side,
A patent characterized in that, when the shape factors of the positive lens and the negative lens are xp and χN, respectively, the following conditions are satisfied: -0,2<xp<2.0 -8.0<XN<-0,6 An attachment lens according to claim 1.