JPS5923314A - Internal focusing zoom lens - Google Patents

Abstract

PURPOSE:To make the construction of a lens barrel simple and compact by consisting a titled lens of the 1st positive lens group, the 2nd negative lens group, the 3rd positive lens group, the 4th negative lens group and the 5th positive lens group, performing variable power and focusing by moving the 4th and the 5th lenses, and performing focusing at the nearer distance by moving the 2nd lens group. CONSTITUTION:The stationary 1st positive lens group G1, the 2nd negative lens group G2 moving on the optical axis, the 3rd positive stationary lens group G3, the 4th negative lens group G4 moving on the optical axis, and the 5th positive lens group G5 moving cooperatively with G4 are provided successively from the object side. The variable power is varied by the relative movement of G4 and G5 and the focusing to a near distance object is accomplished by the movement of G2 to the image side with the compact constitution. The synthesized mangification beta of G4, G5 is determined at 0.5<beta<2.8, and the focal lengths f1, f2, f4, f5 of G1, G2, G4, G5 are set at 0.35<¦f2/f1¦<0.55, 0.5<¦f4/f5¦<0.9, whereby various aberrations are satisfactorily corrected and the compact telephoto lens of EFL 403-790, ENos. 4-8 is obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a zoom lens that can focus within the lens system.

In most conventional zoom lens focusing systems, focusing is achieved by moving the lens group located closest to the object 11111 in front of the variable magnification unit toward the object along the original axis. The force and drag of this Lures group as a focusing group is:
Because it is relatively weaker than the refractive power of gold thread at wide ZM, the amount of movement of the first lens group becomes too large when focusing on the southern limit distance PIit to obtain a constant photographic magnification, and the total length is too large when focusing on short distances. is also longer. For this reason, there was a tendency for the 5'e ht of the principal ray ([111] to decrease significantly with respect to the oblique beam. To avoid this, increasing the [)I refracting power of the first group, the large aperture ratio , but at the same time it becomes difficult
Significant aberration fluctuations occur during limited distance focusing. For this reason, especially in a telephoto zoom lens with a long focal length of all threads in a wide medium, the focal length I'll of m 1 rll' also becomes long, and the amount of movement for focusing becomes increasingly large.
There was a limit to the close-up distance that could be taken, and in order to move the relatively large lens group, which could be as large as the object + 1111, the structure of the chain had to be complicated and thick.

SUMMARY OF THE INVENTION An object of the present invention is to provide an internal focusing zoom lens which eliminates the above-mentioned drawbacks, has a simple structure, and has excellent imaging performance.

The internal focusing zoom lens according to the present invention
to jllI(, fixed 1121st with positive refractive power
group, a second lens group with negative refractive power that can be moved on the optical axis, a fixed third lens group with positive refractive power, 5Y: a fourth lens group with negative refractive power that can be moved on the axis, and A fifth lens group having a positive refractive power and movable on the y-color axis in conjunction with the fourth lens group is 41, and magnification is changed by relative movement of the fourth lens element and the fifth lens group. By doing so, it is possible to focus on objects at a closer distance by using the four apertures of the second lens group for A and A. The movement ftIJ of the second lens group is independent of the movement of the fourth and @5 lens groups, and it is possible to change the magnification in any in-focus state. A substantially parallel beam system is maintained between the second lens group and the third lens group.

In a zoom lens having the structure of the present invention, the above-mentioned difficulties can be overcome, and the lens barrel can be made very thin and compact. Moreover, the curve C emanating from the object point on the axis and outside 1411; the lines are each 111.]
Since there is not much change in the incident height over the entire zoom range, the aberration summer movement can be reduced accordingly.
The result is a bright, compact, and high-performance zoom lens.

In the above basic configuration according to the present invention, it is preferable that the aperture 1" aperture is arranged at a distance from the rear of the second lens group to the front of the fifth lens group. -fNiji, the combined magnification of the fourth lens group and the fifth lens group forming the variable magnification thread is set to β, 0.5<β<2.8...・(
It is desirable to add 1) by 44.

Regarding conditional expression +11, the aperture of 1" is the second lens! 1]
If the lower limit of /ζ, which is located between the lens group and the fifth lens group, exceeds the lower limit, the exit point will be extremely far away, resulting in an undesirable insufficient amount of light at the periphery.

When the upper limit is exceeded, the refractive powers of the fourth lens group and the fifth lens group become too strong, making it difficult to correct various aberrations at the telephoto end. In particular, this is undesirable because axial and extrachromatic chromatic aberrations, that is, the occurrence of secondary spectra, becomes significant.

-Also, let the focal lengths of the lens ttTl and the second lens frame be fl If, respectively, and the focal lengths of the fourth lens group and the fifth lens group f, , f, respectively.
When +1.5 < l f<//f, l < o, c+
It is desirable that each of the moxibustion requirements in (3) be satisfied.

Conditional expression (2) r, i defines an appropriate refraction distribution that can correct various aberrations when focusing at a finite distance. If the upper limit is exceeded, the refractive power of the second lens group as the focusing 5.1 moving group becomes too weak, and when securing a predetermined magnification, the amount of movement becomes large and the overall length becomes long. In addition, the refractive power of the 1121st group becomes too strong, making it difficult to correct spherical aberration when constructing a bright optical system.
If the limit is exceeded, the sky 141 of the 1121st lens group and the second lens group becomes wider, and it becomes difficult to compensate for astigmatism and astigmatism difference at the extreme and close distances, which is not desirable. (3) defines the appropriate AII folding distribution of the variable magnification yarn, and if the lower limit is exceeded, it becomes difficult to correct astigmatism and astigmatic difference A11., which is not desirable.

If the upper limit is exceeded, a fourth lens is used! 11. Movement h1. becomes too large during zooming, and if a large zoom ratio k(N is attempted, the moving lenses fil' will interfere with each other, which is not desirable.

In the above-mentioned group r/4 configuration, each lens l11r is desirably constructed as follows, as in the embodiment described below with reference to i-. The 1121st group (G,) is a biconvex positive lens (■, ,) from the 1st body side to the j direction, a biconvex positive lens (L2) with a stronger curved surface on the object side, and a biconcave lens (L,
). Second lens group (02) as a focusing group
K image 11 Biconcave lens (L,
), a negative meniscus lens (L, ) with its convex surface facing the image side or object 11111, and the third lens group (G3) consists of a single or laminated straight lens (Ln>).The fourth lens group (G4J is a combination of a biconvex lens and a biconcave lens, and includes a meniscus lens with the convex surface facing the object 11111 (L,), a biconcave lens (I,,), and a positive meniscus lens with a completely white convex surface facing the object (L,). The fifth lens group (G, ) consists of two double-convex positive lenses fL4n ), (J
-1+), with the convex surface facing the object 11111 or the image side/
It consists of a laminated lens (L, 2) with this laminated surface 'cH, and the last laminated lens (Let) can also be configured to be separated into a negative lens and a positive lens.

Examples according to the present invention will be described below. From the first embodiment to the third embodiment flJ dimensions e have the following percentage characteristics. The width of the C bundle incident on the 1st run group (G1) remains unchanged, but the F numbers of all yarns change due to zooming and movement.

The effective diameter of the lens group (G,) is determined by a predetermined F number at the wide end. At the wide end, off-axis oblique light flux also
The incident light within this effective diameter (Y; the periphery where only the bundle is sufficient)
; New 1, can be maintained (ilfi.

For this reason, there is no need to make the diameter of the 1 diameter of the 1st lens group CGl) larger than the 1" diameter determined by the F number, making it very con-bag 1.

The specifications of the first to third embodiments are shown below. In each table, rl, r
2. r, 1. ... is the radius of curvature of each lens sequentially from the 'hedron 11, dl, +I2, dq...
・ is the center 11j of each lens and the distance between lenses IIJ and J
, n2, n3... and C2. C2. ν,
... is the d-line of each lens (λ = 587.6 nm
) to) represents the iil folding and Atsube sieve.

(j Q (5
(j1 71- 4艷II 11 1111 ≧ λ ≧ 0 Q Q Q
-m-- "-1 1 r-111 lo -, 3 a, sp,
p, aOko0 Q ○
0/ ・8---'
-A In these embodiments, the fourth lens group (G4) and the fifth lens group
The composite magnification β of the variable power system consisting of the lens group (G,) is 1°2
<Variable in the range β < 2.6. That is, the composite focal length from the first lens group to the third lens group is shorter than the composite focal length of the entire system that can be obtained by zooming.

Therefore, by zooming, the change in the incident height of the light flux passing through the variable magnification system, especially the principal ray, can be reduced.
This is very effective in correcting aberrations. In the first to third embodiments described above, the aperture stop (S) is located at the third lens group (
G,) is 0.5J in front of the first plane.

Note that if a fixed diaphragm (S) is provided behind the fifth lens group, the aperture of this fixed diaphragm can be varied according to zooming, thereby blocking harmful oblique light beams and improving imaging performance.

In the fourth embodiment, as shown in the following table, the composite magnification β of the variable power system includes a point β-1 within the entire zoom area. The F number remains unchanged at 4.0, and the position of the aperture stop (81) is 7 mm behind the final surface of the fourth lens group (G4). Compared to this, the focal length of the entire system is short, so the angle of view is relatively large.In such a case, the composite magnification β of the variable power system should be in the range of 0.5〈β〈1.3. is desirable.

,;　　　　　　　r:;　　　　　CE.

7 〆 〆 1 5-koshi- 5;; j; 5; +j
II II II 1111 II
1111 1111 Ill ζ ζ , g
l::, e ζ:;"i"'h(73--h7-----'---The lens configuration diagrams of the above original ti+2nd, 3rd, and 4th embodiments are respectively Figure 1, Figure 3, Figure 1!5.

Shown in Figure N47, various aberration diagrams fK: Figures 2 and 4.

They are shown in Figure 6 and Skin Figure 8, respectively. In each aberration diagram (
N is the shortest focal length state, (13) is the dnj-nu difference diagram at the infinite union focus in the longest focal length ^IF search, ((1 and (DJ are respectively tl and short focal length h″l;
It is a diagram of various aberrations at the time of near 111'' reduction focusing in the 1 liter shape and the longest focal length state VC. In each aberration diagram, l', i? 17 has a quasi-wavelength (1 line (λ-587.6 nm)
), spherical aberration (Sph ), astigmatism (A
st) and distortion aberration (Dis). Same, object distance d when focusing at short distance. are as stated in the specification table for each example.

As described below, according to the present invention, the lens group closest to the object and the i-3 lens group are fixed, and the movement is caused by the relative # movement of the fourth lens group and the fifth lens group behind the lens thread. Since the magnification is changed and focusing is achieved by moving only the second lens group, the overall length of the lens thread does not change during focusing, the lens barrel structure is simple, and the focus change due to focusing is small. A zoom lens is achieved.

[Brief explanation of the drawing]

Fig. m1, Fig. 3, Fig. 5, and Fig. 7 are lens configuration diagrams of the first to fourth embodiments of the present invention, Fig. 2, Fig. 4, and Fig. 6, respectively.
Fig. 8 shows various aberration diagrams of the first to fourth Ritsuya examples, respectively, (~ is the M short focal length state, and (13) is the various aberrations at infinite union focusing in the longest focal length state, respectively. figure,
(0 and (U are various aberration diagrams during close-range focusing in the shortest focal length H (state) and longest focal length state, respectively. [Explanation of symbols of main parts] G, ... ki, lens group G, ... 2nd lens group G3... 3rd lens group G, ... l!1'!4 lens group G, ... 5th lens group Peak 2 section (A) 3ph A S7
Drs120 tC) Sph ASt Dis
(D) 1=t=40 (△) (B) 1s D no S - A74 prisoner CC) <D) Spear 6 figure (△) <B) SPh Astis 10G cause CC) (D) 1,0008O- (A ) Sp'r+ As+ Sph Ast DI5' iS Spike 8 ((1,) Sph Ast is is

Claims (1)

[Claims] In order from the object side: a fixed 1121st lens group with positive refractive power, a second lens group with negative refractive power that is movable on the optical axis, a fixed third lens group with positive refractive power, and a fixed third lens group that is movable on the optical axis. a fourth lens group having a negative refractive power, and a @5 lens group having a positive refractive power capable of moving on the C11ul in conjunction with the fourth lens group; The magnification is changed by moving relative to the lens group, and the image I of the second lens group is
An internal focusing zoom lens characterized in that full focusing on a closer object can be achieved by moving to l+.