JPS6190120A - Zoom lens - Google Patents

Abstract

PURPOSE:To obtain a zoom lens wide in power variation range and has various aberrations, specially, of distortion and coma are compensated excellently by composing the lens of four positive, negative, positive, and positive lens groups successively from the object side and setting specific conditions. CONSTITUTION:The 1st positive lens group G1, the 2nd negative lens group G2, the 3rd positive lens group G3, and the 4th positive lens group G4 are provided successively from the object side and air gaps among the respective lens groups are varied to constitute a zoom lens which varies in power. Then, the 2nd lens group G2 is composed of the 1st negative meniscus lens element having a convex surface on the object side, the 2nd negative lens element L22, the 3rd biconvex positive lens element L23, and the 4th negative lens element L24 having a large-curvature surface at the object side successively from the object side. Then, inequalities hold, where fw is the shortest focal length of the whole system, fT the longest focal length of the whole system, fn the focal length of each lens element, ra and rb the radii of curvature of the object-side and image-side surfaces of the 3rd element of the 2nd lens group, and DH the distance between the object-side and image-side principal points of the 2nd lens group.

Description

DETAILED DESCRIPTION OF THE INVENTION (Technical Field of the Invention) The present invention relates to a zoom lens for a 35 mm eye reflex camera having a wide variable power range from wide-angle to telephoto.

(Background of the Invention) In recent years, various zoom lenses of this type have been proposed, and in order from the object side, the first lens group has a positive refractive power, and the second lens group has a negative refractive power.
lens group, a third lens group with positive refractive power and a fourth lens group with positive refractive power
Basically, the first, third, and fourth lens groups move toward the object side when zooming from the wide-angle end to the telephoto end. Although these can maintain a certain level of performance, they sacrifice distortion aberration in order to make the lens system more compact and have a higher zoom ratio, and even coma aberration cannot be sufficiently corrected. was difficult to do.

(Statement of the Invention) It is an object of the present invention to provide a zoom lens that has a wide range of zooming from wide-angle to telephoto, while having various aberrations, particularly distortion and coma, well corrected throughout the range of zooming. Our goal is to provide the following.

(Summary of the Invention) As shown in FIG. 1 showing the lens configuration of the first embodiment, the lens group according to the present invention includes, in order from the object side, the first lens group with positive refractive power, the first lens group with negative refractive power, and the second lens group with negative refractive power. 2 lenses x'(, c
z, in a zoom lens that performs magnification by softening a third lens group G3 having a positive refractive power and a fourth lens group G4 having a positive refractive power and changing the air distance between each of these lens groups, the second lens The first component L of the negative meniscus lens with the convex surface facing the object side in order from the object side of the group Gt! I
The second component Lzz of the s negative lens, the third component of the biconvex positive lens
It is composed of component 1-z3 and fourth component 1, 24 of a negative lens having a surface with a stronger curvature on the object side, and further satisfies the following conditions.

(L) 0.25<f, 1/r+<0
．． 6(2) 0.07<l r, l/rT<
0.15(3) 0.25< r 2 / r t
<0.65(4) 0.25< r a /
r T <0.65rb r@ (6) 0.6 < l fz l/ ft3<1.
0(7) 3.0 < f zsa, / l r!
+<30.0(8) 0.05<Dt+/I
f! l<0.15 However, fo: Shortest focal length of the entire system, f: Longest focal length of the entire system, fl: Focal length of the lens group G1, f2: Focal length of the second lens group, f,: Third lens group Focal length f4 of G3: Focal length r,, rl of fourth lens group G4: Radius of curvature f2 of the object-side and image-side surfaces of the third component in second lens group G2. : Focal length of the third component in the second lens group G2 ft5a : Combined focal length of the third and fourth components in the second lens group G2 DM : Object-side principal point and image-side principal point of the second lens group G2 The distance between

These conditions will be explained below.

Conditional expression (1) defines the refractive power of the lens group GI in the present invention. This condition is the lunes group G,
It can be seen as a condition for focusing by extending the
In this case, if the upper limit of this condition is exceeded, the amount of movement of the lens group GI for focusing will become large, and the aperture of the lens will become large in order to photograph objects at short distances, which is generally required. It will pass. On the other hand, if the lower limit of this condition is exceeded, it is advantageous to make the lens system more compact, but on the other hand,
Telephoto i! It becomes difficult to correct chromatic aberration in ;

Furthermore, from the Luns Group G to the 3rd Lens Islands, 74
? It can be seen as a modification of the afocal variable power system in terms of t, and from this point of view, when the lower limit of this condition is exceeded,
The refractive power of each group in the variable magnification system becomes too strong, and the Petzval sum becomes negative, making it difficult to correct field curvature.

Condition (2) is that the second lens r! primarily plays the role of a variator for variable magnification. It concerns T c z .

If the lower limit of this condition is exceeded, it is advantageous for making the lens system more compact, but on the other hand, the spherical aberration at the telephoto end increases and it becomes difficult to balance it with the coma aberration.
It also becomes difficult to correct chromatic aberration of magnification. Furthermore, aberration fluctuations during zooming also increase. However, if the upper limit of this condition is exceeded, the total length of the second lens group G2 becomes long, making it difficult to make the entire lens compact.

Conditional expressions (3) and (4) define the practical optimum power distribution of the third lens group G and the fourth lens group G4. If each of these conditions exceeds the upper limit,
As the total length of the lens increases, the aperture of the aperture also increases, resulting in an increase in the size of the entire lens.Conversely, if the lower limits of these conditions are exceeded, it becomes difficult to correct various aberrations.

In the second lens group G2 of the zoom lens according to the present invention, the magnification of this group and the height of incidence of oblique rays on this group vary greatly during zooming.
By arranging a lens with positive refractive power as the third component in the second lens group G2 with negative refractive power, the second lens I! '1
- It is necessary to sufficiently correct aberrations in G2. conditions(
5) is such a second lens group G! This defines an optimal shape in which the positive lens as the third component has a biconvex shape. If the lower limit of this condition is exceeded, the position of the rear principal plane of the second lens group G2 will move toward the object side, and especially the distance between the second lens group G2 and the third lens group G3 at the telephoto end. Since tit L becomes small, it becomes necessary to use a zoom lens with a high variable magnification ratio. Furthermore, it becomes difficult to correct off-axis aberrations near the shortest focal length. On the other hand, if the upper limit of this condition is exceeded, it becomes difficult to correct the spherical aberration in the second lens group G2 and the third lens group G.

Condition (6) defines the optimal power distribution of the third component in the second lens group G2, and together with the above condition (5), it is necessary to satisfactorily tilt spherical aberration and coma aberration especially at the telephoto end.
It is also used to correct various off-axis aberrations on the wide-angle side with a good kr. That is, if the upper limit of this condition is exceeded, the refractive power of each lens component in the second lens group G2 becomes too strong, making it difficult to correct various aberrations, and the tolerance for manufacturing errors of each lens becomes strict. This makes it difficult to mass produce with stable performance. On the other hand, if the lower limit of this condition is not met, aberrations can be corrected if the zoom lens has a small magnification ratio or the angle of view at the shortest focal length is not very large, but high-magnification zooms including wide-angle In the case of lenses, each lens has insufficient refractive power, making it difficult to correct aberrations.

Condition (7) defines the optimal range of the combined focal length of the third and fourth components in the second lens group GZ.

If the lower limit of this condition is exceeded, the rear principal plane of the second lens group G2 will be biased toward the object side, and in order to ensure the distance between the second lens group G2 and the third lens group G3, the third lens group G, In addition, if the upper limit is exceeded, the refractive power of each of the six lens components of the second lens group becomes weak, and the aberration correction in the second lens group G2 becomes insufficient. turn into.

Condition (8) defines the optimum principal point interval between the front side and the rear side of the second lens group G2. Second lens t: j c
; has negative refractive power, so the closer the distance between the positive lens component as the third component and the negative refractive power components on both sides, the weaker the refractive power of each negative refractive power component is, and the more aberrations occur. This is advantageous for correction. However, if the distance between the principal points is made too large, the entire lens system becomes elongated.

In the configuration of the present invention as described above, the fourth lens group G4 is further arranged in order from the object side: the first component L41 of the positive lens;
The second component L of a negative meniscus lens with a convex surface facing the object side
4z, the third component L43 of the positive lens and the fourth component L43 of the positive lens
When the radius of curvature of the object-side and image-side surfaces of the second component L4□ in the fourth lens group G4 is r(+", J--rc It is desirable that the following conditions be satisfied.By forming the second component of negative refractive power in the fourth lens group G4 into a meniscus shape with the convex surface facing the object side, off-axis aberrations, especially in the shortest focal length state, can be reduced. It becomes possible to perform correction better.

(Example) Examples according to the present invention will be described below.

Both the first and second embodiments of the present invention have lens configurations as shown in FIG.
It has specifications of 35 mm and an F number of about 3.5 to 4.5. Figure 1 shows the peripheral rays from an object point at infinity on the axis and the rays from an object point at off-axis infinity at the maximum angle of view, and also shows how each lens group changes magnification from the wide-angle end to the telephoto end. The trajectory of the movement is also shown.

Tables 1 and 2 below show specifications of the first example and the second example. In each table, the leftmost number represents the order from the object side. The refractive index and number are respectively for the d-line (λ=
587.6r+m').

Table I C 1st Example) Focal length f = 35.7 to 130.95F number 3
．． 57~4.58 Table 1 <Vt) f1= 70.20 fzs = 23
．． 84fz =17.06 fz+4=
82.51f, = 46.05 f4 = 75.90 Table 2 (Second Example) Focal length f = 35.7 to 130.95F number 3
．． 57-4.58 Table 2 (continued) f, = 70.20 fz3= 19
．． 34fz = 17.06 fzsn
= 64.8Of, = 46.05 f4 = 75.90 The aberration diagrams for the above first example are shown in Fig. 28 and Fig. 2B.
As shown in the figure. FIG. 2A shows spherical aberration, astigmatism, and distortion aberration, and FIG. 2B shows lateral chromatic aberration and lateral aberration. Similarly, FIGS. 3A and 3B show aberration diagrams for the third embodiment.

Now, in the third embodiment of the present invention, the fourth component L2 in the second lens group G2 is as shown in FIG.
4 is composed of a biconcave negative lens separated from each other and a positive meniscus lens with a convex surface facing the object side, and
The second component L3□ in the third lens group G3 is composed of a biconvex positive lens separated from each other and a negative meniscus lens with a convex surface facing the image side. Figure 4 shows the peripheral rays from an object point at infinity on the axis and the rays from an object point at off-axis infinity at the maximum angle of view, and also shows how each lens group changes magnification from the wide-angle end to the telephoto end. The trajectory of the movement is also shown.

Table 3 below shows the specifications of the third example.

In the table, each symbol is the same as in Tables 1 and 2 above.

Table 3 (vt) f+ = 70.20 fiz =
27.71fz = 17.06f
z3<=92.00fa=46.05 f4=75.90 Aberration diagrams of the third embodiment are shown in FIGS. 5A and 5[3]. FIG. 5A shows spherical aberration, astigmatism, and distortion aberration, and FIG. 5B shows lateral chromatic aberration and lateral aberration.

From the aberration diagrams, it is clear that in all the examples, distortion aberration, coma aberration, and other various aberrations are sufficiently well corrected, and that they have practically excellent imaging performance even during zooming.

(Effects of the Invention) As described above, according to the present invention, various aberrations, particularly distortion and coma, are well corrected over the entire zooming range, while having a wide zooming range from wide-angle to telephoto. A zoom lens is achieved.

[Brief explanation of drawings]

FIG. 1 is a lens configuration diagram of a first embodiment and a second embodiment according to the present invention, FIGS. 2A and 2B are various aberration diagrams of the first embodiment, and FIGS. 3A and 3B are a lens configuration diagram of a second embodiment. Examples of various aberration diagrams,
Figure 4 is a lens configuration diagram of the third embodiment, Figure 5A, and Figure 5.
Figure B is a diagram showing various aberrations of the third embodiment. [Main part i,]: Explanation of II] [;,... 1st lens group (-2... 1 in the 2nd lens group,... 3rd lens group G,... 4th lens group

Claims (1)

[Claims] In order from the object side, a first lens group G_1 with positive refractive power, a second lens group G_2 with negative refractive power, and a third lens group G with positive refractive power.
In a zoom lens which has a fourth lens group G_4 having a positive refractive power and a fourth lens group G_4 having a positive refractive power, and which performs magnification by changing the air distance between each of these lens groups, the second lens group G_2 is arranged in order from the object side. It has a first component of a negative meniscus lens with a convex surface facing toward, a second component of a negative lens, a third component of a biconvex positive lens, and a fourth component of a negative lens having a surface with a stronger curvature toward the object side. A zoom lens characterized by satisfying each of the following conditions. (1) 0.25<f_w/f_1<0.6 (2) 0.07<|f_2|/f_T<0.15 (3)
0.25<f_3/f_T<0.65(4)0.25<
f_4/f_T<0.65(5)0.08<(r_b+
r_a)/(r_b-r_a)<0.9(6)0.6<
|f_2|/f_2_3<1.0 (7) 3.0<f_2
_3_4/｜f_2｜30.0(8)0.05<D_H
/|f_2|<0.15 However, f_w: Shortest focal length of the entire system f_r: Longest focal length of the entire system f_1: Focal length of the first lens group G_1 f_2: Focal length of the second lens group G_2 f_3: Third Focal length f_4 of lens group G_3: Focal length f_2_3 of fourth lens group G_4: Radius of curvature of the object-side and image-side surfaces of the third component in second lens group G_Z f_2_3: Third component in second lens group G_2 Focal length of component f_2_3_4: 3rd and 4th lens in second lens group G_2
Component composite focal length D_H: The distance between the object-side principal point and the image-side principal point of the second lens group G_2.