JPH03127013A - Compact zoom lens - Google Patents

Abstract

PURPOSE:To compose the compact zoom lens for a lens shutter camera of a small number of elements by composing the front group of one positive lens and one negative lens and the rear group of one negative lens. CONSTITUTION:The zoom lens consists of the front group which has positive refracting power and the rear group which has negative refracting power in order from the object side and the gap between the front group and rear group is varied to vary the focal length of the whole system. In such a zoom lens, the front group consists of one positive lens and one negative lens and the rear group consists of one negative lens. Consequently, while high optical performance is maintained, the compact zoom lens can be composed of a small number of elements.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a zoom lens, and more particularly to a zoom lens for a lens shutter camera with a built-in zoom lens.

In order to make a lens shutter camera with a built-in zoom lens more compact and lower in cost, there is a demand for a more compact and lower cost photographic lens. In order to make the lens system more compact, including the amount of movement for zooming, it is necessary to increase the refractive power of each group, but increasing the refractive power while maintaining performance requires increasing the number of lenses. It can be said that the direction is to On the other hand, in order to reduce costs, it is effective to reduce the number of lenses.

In this way, there are many conflicting elements involved in making a lens system more compact and reducing its cost.

In view of this situation, an object of the present invention is to construct a compact zoom lens for a lens-shutter camera with a small number of lenses.

In order to achieve the above-mentioned purpose of calculating i, in the present invention, in order from the object side,
In a zoom lens in which the front group has a positive refractive power and the rear group has a negative refractive power, and the focal length of the entire system is changed by changing the distance between the front group and the rear group, the front group is The rear group is configured to consist of one negative lens and one positive lens.

It is preferable that the front group has at least one aspherical surface that satisfies the following conditional expression (2).

When the maximum effective diameter of the aspherical surface is y, □, 0.7y□*
< y < 1-0 )' a □ For any height y in the vertical direction of the optical axis, -0,03<ki・(N′ −N)・ .

(x (y) −xe(y) }<0 ・−・・−・
・・・−・・■Here, Qi: Refractive power of the front group N: Refractive index of the aspherical object side medium No.: Refractive index of the aspherical image side medium x (y): Surface shape of the aspherical surface x0(y): Reference spherical shape of aspherical surface However, 10ΣA1. ! 1m r: Reference radius of curvature of the aspherical surface ε: Quadratic surface parameter Ai: Aspherical surface coefficient 7: Paraxial radius of curvature of the aspherical surface 1 (i −7+ 2 A·).

The above conditional expression (■) means that the positive refractive power becomes weaker (the negative refractive power becomes stronger) at the periphery of the aspherical surface in the front group,
This is a condition for correcting spherical aberration. When the upper limit is exceeded, spherical aberration tends to be undercorrected over the entire zoom range; when the lower limit is exceeded, the spherical aberration tends to be overcorrected over the entire zoom range.

Further, it is preferable that the rear group has at least one aspherical surface that satisfies the following conditional expression (2). Conditional formula (■) is 0.8 when the maximum effective diameter of the aspherical surface is h18.
3',,X<y<1. For any height y in the vertical direction of the optical axis, Oy, &X, −o, io<i・(N′ −N)・,.

(x (y) x0(y) }<O・・・・−・
......■Here, ψ1: Refractive power of the rear group.

The above conditional expression (■) means that the negative refractive power of the aspherical surface in the rear group is weaker (the positive refractive power is stronger) at the periphery,
This is a condition for correcting distortion and field curvature in a well-balanced manner. When the upper limit is exceeded, the distortion aberration at the wide-angle end takes on a large positive value, and when the lower limit is exceeded, the image plane tends to be significantly curved in the negative direction over the entire zoom range.

It is desirable that all the aspheric surfaces in the front group satisfy the following conditional expression (2).

Conditional expression (2) is: -0,02<Ki・(N" -N)・ ,.

< x (y) x0 (y) ><0.01 −・
・－・－・・・・・・■.

If the upper limit of conditional expression (2) is exceeded, the annular spherical aberration will have a large negative value, and a shift in the focus position due to aperture will become a problem. If the lower limit is exceeded, the effect of correcting the spherical aberration on the annular beam becomes excessive, making it difficult to correct various aberrations and spherical aberration in a well-balanced manner, and the spherical aberration tends to take on an undulating shape.

It is desirable that all the aspheric surfaces in the rear group satisfy the following conditional expression (2).

Conditional formula (■) indicates that the maximum effective diameter of the aspherical surface is y. 1X, for any height y in the direction perpendicular to the optical axis, y<o, sy□, −0,05<9)・(N″−N)・.

<x(y)−xe(y)><0.02
−・・・−・・・・・・■.

When the upper limit of conditional expression (2) is exceeded, the tendency for positive distortion and positive deviation of the curvature of field increases in the intermediate field angle band from the wide-angle end to the intermediate focal length region. Further, when the lower limit is exceeded, negative distortion becomes large from the intermediate focal length range to the telephoto end, and in addition, the negative shift tendency of the curvature of field becomes significant in the entire zoom range.

Also, in order to keep the back focus at an appropriate size,
It is preferable that the front group consists of a negative lens and a positive lens in order from the object side. If the back focus becomes too short, the effective diameter of the optical path of the lens located closest to the image plane becomes too large. , the camera becomes larger.

The axial distance between the front group and the rear group at the telephoto end is preferably a size that satisfies conditional expression (2) shown below.

0.1<ΔT+*/ f v <0.4 −■
However, ΔT1 Distance on the optical axis from the surface of the front group closest to the image plane to the surface of the rear group closest to the object side on the optical axis: Focal length of the entire system at the telephoto end Beyond the upper limit of the above conditional expression (■) ΔTI ! When becomes large,
The overall length of the lens (distance from the front apex of the lens to the film surface at the wide-angle end! 18K) becomes too large. Furthermore, when the lower limit is exceeded and ΔTit becomes small, off-axis coma aberration mainly at the telephoto end increases, and optical performance deteriorates.

It is preferable that a movable light flux regulating plate is provided on the object side of the front group in conjunction with zooming. By providing a movable light flux regulating plate, at the wide-angle end, the amount of peripheral light can be reduced without regulating the peripheral luminous flux too much. By moving the light flux regulating plate in a direction away from the front group from the intermediate focal length state to the telephoto end, it is possible to effectively cut out the coma flare of the intermediate light flux.

Further, it is preferable that the zoom lens according to the present invention satisfies the following conditional expression (2).

0.40 < f t / f w <0.75
■However, f8: Focal length of the image side lens of the front group f8: Focal length of the entire system at the wide-angle end If f2 becomes smaller than the upper limit of the above conditional expression (■), the coma flare of the intermediate light beam on the wide-angle side will increase. .

Furthermore, when f2 increases beyond the lower limit, the coma flare of the intermediate light beam on the telephoto side increases, and the optical performance deteriorates.

Furthermore, among the lenses constituting the zoom lens of the present invention,
It is preferable that at least one lens has an aspherical surface on both sides.

Embodiments of the compact zoom lens according to the present invention will be shown below.

However, in each example, r l"" r & is the radius of curvature of the surface counted from the object side, d1 to d are the distances between the axial surfaces counted from the object side, and N1 to N and shi1 to shi3 are The refractive index and Atsube number of each lens for the d-line as counted from the object side are shown. Also, r is the focal length of the entire system, and FNO is the open F-number.

In addition, in the examples, a surface with a radius of curvature marked with * indicates that it is an aspherical surface, and the surface shape of the aspherical surface (
x (y) ).

<Example 1> f = 39.3 to 51.8 to 68.2 F,, = 4.
1~5.3~7.0Σd -40,153~38.14
5~38.220 14mm (losing rl: g -0,27563X108a -
-0,57377x 10- 'A, --0,287
91xlO-'rg: As""0.25981xlO-'AIe =0
．． 71952xlO-'A+z"' 0.179
10X10-”ε=-0,95676 A4=0.32319X10-' Ah=0.31975 x 10-'As--0
．． 29096xlO-” A1゜--0,86424X 10 minus 0Alt =
0.16278X10-"ε=0.11348X10 A4=0.34973X10-'^i=0.13838xlO-"As=0.65555xlO-' A,. = -0,92932X 10- "Alg"
0.48225X10-th ε-0,25432x 10 ^n-0.55479X10-'16--0.16122xlO-' A, depth 0.22221X10-" Al6 --G, 53141xlO-" A+ z -0
,26081X 10-th ε--0,22241x
I.

A4-0.26936 X 10-'^&=0.27
385X10- @as--0.25504xtO-” A, ・=0.11840X10-IOAth-0,11
070X10-"<Example2> f -39,3~55.2~77.5 FNO-4,0~5.7~8.0 Σd wealth 41.818~38.975~40.958 agri.
4 losses rl: e -0,15018X10A4--
0.32667xlO-' Ah--0,19314x 10- "^, --0.2
6162xlO-MaAt@-0, 75722xlO-' rt: r4: rs: rh: AIz = 0.13941X10-"ε=-0,
94829 A.
0020X10 A, = 0.41090XlO-' Re = 0.37818X10-' A, = 0.58283X10-9 Ago = 0.36793xlO-10A1□ =-
0,34580X10-' 2ε=0.27377X1
0 A 4= 0.48509 x 10-'A, =
-0,23791x 10-”A, -0,21497
X10-” ^, .=-0,42474X10-1”A1□ =0.
17971
9x 10 A, = 0.29356X10-'A&=0.29483X10-' ^s = 0.25430
0.79055X10-" Adz = 0.40582X10--4 <Example 3> f = 39.3-51.8-68.2 F8° = 3.6-4.7-6.0 ds 1.044 N+ 1.72900 53.48 r, $ 115.276 Σd = 41.789 ~ 53.664 ~ 71.663 consecutive 14 stabbing losses r,: ε = -0, 17535 A4--〇, 29592X10-' A6-0 .12066 X 10-'As''-0
,20055X 10-'Aha''=0.821
77X10-”Alt=-0,11741X10-
"rt: a -0,23617X10r4
: rS : rh : A,=0.27941X10-'A,=0.54904X10-'8s=0.98187X10-' ^,. =0.84612X10-” Alt =-0,11309X10-”ε=0.13
359X10 Aa=0.43666xlO-'A&-0,42178X10-'as=0.71801X10-' Aha =0.18344X10-IOA1□ =0
．． 13664X10 minus 2 ε=0.26567X10 A4=0.24062X10-' Al= 0.21968X 10-'Aa=0.13
828xlO-' A1゜= -0,88598x 10- "＾l□=
0.13382
73X10 A, =0.17944 x 10-'A! =0.55
391X10-' A, = -0,18417XlO-'' A1゜=0.11461X10-0 ^+t = 0.27114X10-0 Figures 1 to 3 show the countries in which the lenses are configured corresponding to Examples 1 to 3 above. (B) shows a light flux regulating plate.

This light flux regulating plate (B) effectively cuts coma flare on the telephoto side by moving on the optical axis in conjunction with zooming.

The diameter of the light flux regulating plate (8) shown in FIGS. 1 to 3 is 1.2 times larger than at least one of the axial light flux width at the wide-angle end and the axial light flux width at the telephoto end. It is preferable that it is below, which means that if it exceeds the above 1.2 times,
This is because it becomes impossible to effectively cut out the coma flare of the intermediate light beam especially at the telephoto end. Furthermore, it is preferable that the diameter of the light flux regulating plate (B) is 1.05 times or less the width of the axial light flux at the telephoto end, since coma flare in the off-axis light flux at the telephoto end can be effectively cut.

Further, it is preferable that the light flux regulating plate (B) moves so as to widen the air distance from the front group during zooming from the wide-angle end to the telephoto end. This makes it possible to cut out coma flare at the telephoto end without reducing the amount of peripheral light at the wide-angle end.

When zooming from the wide-angle end to the telephoto end, the light flux regulating plate (B) is preferably moved in unison with the rear group or at a constant ratio of the movement of the rear group, as this facilitates the construction of the lens barrel. .

In addition, in FIGS. 1 to 3, arrows indicate the light flux regulating plate (B),
The movement of the front group and the rear group from the widest angle end (S) to the stationary far end (L) is schematically shown.

Embodiment 1 includes, in order from the object side, a light flux regulating plate (B), a front group consisting of a first lens on the object side that is more powerful than a concave negative meniscus lens, and a positive second lens with strong power on the image side; and a rear group consisting of a concave negative third lens. Note that the object-side surface and image-side surface of the negative first lens, and the positive second lens
The image side surface of the lens and the object side surface and image side surface of the negative third lens are aspheric surfaces.

Embodiment 2 includes, in order from the object side, a light flux regulating plate (B), a front group consisting of a first lens consisting of a concave negative meniscus lens on the object side and a positive second lens with strong power on the image side; It consists of a concave negative third lens and a rear group. Note that the object-side surface and image-side surface of the negative first lens, and the positive second lens
The image side surface of the lens and the object side surface and image side surface of the negative third lens are aspheric surfaces.

Embodiment 3 includes, in order from the object side, a light flux regulating plate (B), a first lens having a concave negative meniscus lens on the object side, and a front group having a positive second lens with strong power on the image side; It consists of a biconcave negative third lens and a rear group. Note that the object-side surface and image-side surface of the negative first lens, and the positive second lens
The image side surface of the lens and the object side surface and image side surface of the negative third lens are aspheric surfaces.

Figures 4 to 6 are aberration diagrams corresponding to Examples 1 to 3, in which (S) is the aberration at the wide-angle end focal length, (M) is the intermediate focal length, and (L) is the aberration at the telephoto end focal length. It shows.

Also, the solid line (d) represents the aberration for the d-line, and the dotted line (
SC) represents the sine condition, and the dotted line (D?I) and solid line (O5) represent astigmatism on the meridional and sagittal surfaces, respectively.

Tables 1 to 3 correspond to Examples 1 to 3, respectively, and show the conditional expression % expression %()xe(y)1*6・(N '-N)・
'(x(y)-x.(y)).

Table 4 also shows ΔT in conditional expression (■) in Examples 1 to 3.
I*/ f t indicates the value of fz/fs* in conditional expression (2).

Table 0 Example 1) Table 2 (Example 2) Table (Example 3) As shown above, Examples 1 to 3 have a focal length of 38 to 70 m.
The main specifications are 5.38 to 80-1. No conventional zoom lens with this specification has a three-element configuration.

However, according to the present invention, the number of lens components can be reduced to three, and the total length of the lens can be shortened.

As described above, according to the present invention, it is possible to realize a compact zoom lens with a small number of lenses while maintaining high optical performance.

For example, the above-mentioned zoom lens having a zoom ratio exceeding 1.7 can be realized with a total of three lenses, two in the front group and one in the rear group. Moreover, if the zoom lens according to the present invention is applied to a lens shutter camera with a built-in zoom lens, the camera can be made more compact and lower in cost.

[Brief explanation of the drawing]

FIG. 4, FIG. 2, and FIG. 3 are respectively Embodiment 1 of the present invention.
3 is a lens configuration diagram corresponding to FIG. Figure 4. 5 and 6 are aberration diagrams corresponding to Examples 1 to 3, respectively. Applicant Minolta Camera Co., Ltd. Agent

Claims (3)

[Claims] (1) A zoom system that consists of a front group with positive refractive power and a rear group with negative refractive power in order from the object side, and changes the focal length of the entire system by changing the distance between the front group and the rear group. A zoom lens characterized in that the front group consists of one positive lens and one negative lens, and the rear group consists of one negative lens. (2) The zoom lens according to claim 1, characterized in that the front group has at least one aspherical surface that satisfies the following conditional expression: The maximum effective diameter of the aspherical surface is y_m_a_x. When, 0.
7y_m_a_x<y<1.0y_m_a_x
)−x_0(y)}<0 where, ψ_1: Refractive power of the front group N: Refractive index of the aspherical object-side medium N': Refractive index of the aspherical image-side medium x(y): Refractive index of the aspherical surface Surface shape x_0(y): Reference spherical shape of aspheric surface However, ▲ There are mathematical formulas, chemical formulas, tables, etc. ▼ ▲ There are mathematical formulas, chemical formulas, tables, etc. ▼ r: Reference radius of curvature ε of aspheric surface: Quadratic surface parameter Ai : Aspheric coefficient ■: Paraxial radius of curvature of aspheric surface (1/■=1/r+2A_2). (3) The zoom lens according to claim 1, characterized in that the rear group has at least one aspherical surface that satisfies the following conditional expression: The maximum effective diameter of the aspherical surface is y_m_a_x. When, 0.
For any vertical height y of the optical axis such that 8y_m_a_x<y<1.0y_m_a_x, −0.10<ψ_2・(N′−N)・d/dy{x(y
)−x_0(y)}<0 where, ψ_2: Refractive power of the rear group N: Refractive index of the aspherical object-side medium N': Refractive index of the aspherical image-side medium x(y): Refractive index of the aspherical surface Surface shape x_0(y): Reference spherical shape of aspheric surface However, ▲ There are mathematical formulas, chemical formulas, tables, etc. ▼ ▲ There are mathematical formulas, chemical formulas, tables, etc. ▼ r: Reference radius of curvature ε of aspheric surface: Quadratic surface parameter Ai : Aspheric coefficient ■: Paraxial radius of curvature of aspheric surface (1/■=1/r+2A_2).