JPS587610A - Short distance aberration change correction system of telephoto zoom lens system - Google Patents

Abstract

PURPOSE:To obtain a compact lens system, by moving the front group and the rear group so as to satisfy prescribed conditions when focusing a finite object distance, in a focusing lens system which consists of the front group and the rear group having positive and negative refractive power, respectively. CONSTITUTION:A focusing lens system is divided into the front group having positive refractive power, so as to satisfy inequalities I, II. In this state, when focusing a finite object distance, the front group and the rear group are moved in order to satisfy the inequality III. In this regard, fF, fp, DELTA, Xp and Xn in these inequalitiesI-III denote a focal distance of the whole lens system, a focal distance of the whole lens system, a focal distance of the front group, a space between the front and rear groups in the finite object, the quantity of feed of the front group, and the quantity of feed of the rear group, respectively.

Description

DETAILED DESCRIPTION OF THE INVENTION An object of the present invention is to provide a method of correcting distance aberration changes in a telephoto zoom lens.

Conventional telephoto zoom lenses generally consist of, from the object side, a focusing lens system, a bar 1 eta system that covers the variable magnification lens, a compensator thread that keeps the focal position constant, and a II lens system. For finite objects, focusing was achieved by letting out the entire focus indwelling lens thread.

However, in this system, when a telephoto zoom lens is used, the spherical aberration and the curvature of field change greatly on the W point side, resulting in degraded performance at the shortest shooting distance. In order to reduce this change in near-field aberration, it is sufficient to reduce the occurrence of aberration within the focusing lens M.
If this is attempted, the number of lenses in the focusing lens system must be increased, or the power must be reduced, leading to an increase in the size of all lens threads.

The present invention provides positive refractive power 't in a telephoto zoom lens.
By dividing the focusing lens thread into two groups (front and rear groups), moving the entire focusing system, and slightly changing the front tk distance, changes in near-field aberrations can be reduced. However, all the elements of the lens were made compact, and at the same time, the performance from the limited object distance to the shortest shooting distance was able to be corrected with excellent performance.

The present invention will be explained in detail below.

The present invention provides the following conditional expression (11, (
When dividing the lens thread into a front group with positive refractive power and a front group with negative refractive power so as to satisfy 21, the finite object distance X! This is a short-distance aberration change correction method for the telephoto zoom lens thread that moves the front and rear groups so as to satisfy the following conditional expression (31) when four-point focusing is performed.

However, fF two focusing lens system focal length fp: Focal length Δ of the front group of the focusing lens system: Distance between the front and rear groups of the focusing lens thread in an infinite object Xp: Feeding lid of the front group of the focusing lens thread Xn+Focus Lens System tIt Group Extension Amount Next, each of the above conditions will be explained.

Condition (11) Concerning the power arrangement within the 7-lens thread, if the upper limit of condition (1) is exceeded, the positive power of the front group will become too strong and the occurrence of spherical aberration will increase, and if the lower limit is exceeded. If it exceeds this, it goes against miniaturization.

Condition 12) is related to the distance between the front groups of the focusing lens thread, and if the upper P[i of condition (2) is exceeded, it becomes difficult to correct the spherical aberration generated in the front group with all the rear groups, and the lower limit If it exceeds this, the distance between the front and rear groups will be lost at the shortest photographing distance.

Condition (3) is related to the movement method of the Hough Aucasing V-lens thread.If the upper limit of condition (3) is exceeded, the distance between the front and rear groups will widen at short distances, and the spherical aberration on the long point side will become under. This will further intensify this trend. Moreover, if the lower limit is exceeded, the correction will be excessive, resulting in excessive spherical aberration, and it will also be difficult to correct chromatic aberration.

An application example of the non-inventive method described above will be described below.

Here, fk-1 point distance, ω is half I! r is the radius of curvature, d is the lens thickness or distance between lens surfaces, the refractive index of nFid-Lin-, and ν is the Abbe number.

Example FNOl + 4.6 f=x38~292 ω
=9.0°~4.2°rd n 9 -161.880 2.80 1.61800
63.410 100,,'EO5,00 11-195,2203,001,6180063,4
1262,80Q 5. BO1, BO31B 2
5.413 1B9. '1738 54.04~2'i
', 51~1.3114 105, 'i'38 B
, 30 1.49700 81.615-105. '7
38 0.2016 111.252
5.20 1.61800 63.417
-476.055 0.201B '7
0.508 '9.50 1.61800
63.419 -'i'0.50B 2.
50 1. '74950 35.320 6B
,000 4. '73~14.41~26.382
1 -104.800 2.50 1.72
916 54. 'i'22 190'i', 00
0 0.2023 36.900 3.
80 1.51112 60.524
52.200 31.3'725 -245.0
00 3.50 1.6E1893 31.
126 -69.9'70 20.12'7
-29.920 2.00 1.88300
40.828 -89.240 0.202
9 1'76,'700 3.50 1.80
518 25.430 -234.000 Configuration diagram of 44 zoom lens thread with the above data 'fm
As shown in Figure 1, in this example, the front group of the focusing lens thread consists of a first positive lens that is convex toward the object from the object side and a second positive lens that is biconvex, and the rear group is a negative lens that is biconcave. It consists of a convex 3-positive lens that is convex to the object. This telephoto zoom lens uses an uninvented short-range aberration correction method.
Fig. 2 shows an aberration diagram at an imaging distance of 2.5 m on the silver dot side when -. Xpu at this time 23.03, X
n is 24.03 and d4 is 2.63. FIG. 16 is an aberration diagram at a projection distance of 2.5 m on the long focal point side when the entire focusing lens thread is let out in the telephoto zoom lens thread.

The angle of view (3, 30) &-1 in Fig. 2.6 is a half L [i11 angle] of the principal ray at a shooting distance of 2.5 m.

According to the present invention, as is clear from the aberration diagrams in FIGS. 2 and 6, aberration changes during short distance fine movement on the long focal length side can be corrected well.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a telephoto zoom lens system applied to the method of the present invention, and FIG. 2 is a diagram showing the photographing distance of 2.5 mm on the long detail point side when the lens thread of FIG. 1 and the distance aberration change correction method are adopted. Aberration diagram at 5 m, Fig. 6 is Fig. 1 77) V 7 s, %
When the entire focusing lens thread is fully paid out! It is an aberration diagram at an imaging distance of 2.5 mm on the fc non-point side. Umugi 1 Mine

Claims (1)

[Claims] In a focusing lens system having a positive refractive power, the focusing lens thread is connected to a front group having a positive refractive power and a negative refractive power so as to satisfy the following conditional expressions 111 and 121. When divided into a temporary group with a force of 1, the close-range aberration of a telephoto zoom lens system is such that the front and rear groups are moved so as to satisfy the following conditional expression (3) when focusing at a finite object distance. Change correction method. where fF: my distance of the focusing lens thread mf: the swallow and trailing distance of the front group of the focusing lens thread Δ: the distance of the focusing lens in an infinite object Xp: the front of the focusing lens thread Bare weight of the group x 7L: Feeding amount of rear group of force shining lens thread