JPS62186215A - Auxiliary lens system - Google Patents

Abstract

PURPOSE:To obtain a compact auxiliary lens system for a photographing lens whose whole length is shorter than a focal distance by setting up the focal distance of the 1st lens group almost equally to that of a focusing lens group in a photographing lens system, and at the time of focusing, delivering the 1st lens group unitedly with the focusing lens group in the photographing lens system. CONSTITUTION:The focusing device having the auxiliary lens system 2 is arranged adjacently to the photographing lens system 1 to be a zoom lens and the 1st lens group 4 in the auxiliary lens system 2 having almost the same focal distance as the focusing lens group 3 in the photographing system 1 is coupled with the focusing lens groups 3 each other and unitedly delivered by a focusing motor 5. A focusing detecting element 6 is arranged on a focus position of the lens system 2 and the drive of the focusing motor 5 is controlled by an output signal from the element 6. When the lens system 2 is focused on the element 6, a driver 7 and a control device 8 in the element 6 control the lens system 1 so that the lens system 1 is focused on a photographing surface 9.

Description

DETAILED DESCRIPTION OF THE INVENTION Object of the Invention (Field of Industrial Application) This invention relates to an auxiliary lens system that is moved together with an imaging lens for purposes such as focusing.

(Prior art) For purposes such as distance measurement for video cameras and still cameras and focusing for real image finders, an auxiliary lens consisting of two positive and negative lens groups separated by an air distance is installed in addition to the lens. The focal length of the positive lens group disposed on the object side is approximately equal to the focal length a of the focusing lens group of the imaging lens system, and by extending the positive lens group and the focusing lens group as one body, the imaging lens A focusing device in which an auxiliary lens is brought into focus at the same time as focusing is known.

-In a focusing device having such an auxiliary lens, the focus detection accuracy of the auxiliary lens improves as the focal length of the entire auxiliary lens becomes longer.

For example, in the case of a finder system that detects the amount of blur on the focal plane, if the F number is constant, the longer the focal length, the shallower the depth of field, and the easier it is to detect the amount of blur. Furthermore, even when using a pupil-divided distance measuring element, the circular accuracy increases as the size of the iron increases.

In the above-mentioned known auxiliary lens system, by making the rear group a negative lens group among the two lens groups constituting the lens system, the combined focal length with the positive front group can be made longer than that of the camera lens. ing.

However, when trying to construct an auxiliary lens system with a long focal length that can provide sufficient focusing accuracy, the lens system ends up having a long overall length, despite having a relatively advantageous telephoto type lens configuration. I end up.

Also, since the front group of this auxiliary lens system moves as one unit with the focusing lens group of the imaging lens,
Naturally, it is desirable for the auxiliary lens system to be placed close to the lens during photography, but the imaging lens system also has parts such as an auto iris and zoom motor mounted on its rotary shaft. The auxiliary lens system that is used is particularly required to be compact, but it is insufficient in this respect as well. The objective is to obtain an auxiliary lens system for a focusing device that is compact and has a short overall length compared to the focal length.

Structure of the Invention (Means for Solving Problems) As described above, the auxiliary lens system of the present invention is provided with an auxiliary lens system having a focus detection element on its focal plane separately for the photographing lens system, A focusing device that brings the auxiliary lens system into focus at the same time as the imaging lens by extending a part of the auxiliary lens system in conjunction with the focusing lens of the lens system being extended for focusing. In order from the object side, a first lens group that has a positive refractive power and moves in the direction of the original axis for focusing, a fixed second lens group that has a positive refractive power, It has a three-group configuration with a fixed third lens group having negative refractive power, and the focal length f1 of the first lens group is approximately equal to the focal length of the focusing lens group of the imaging lens system. The first lens group is extended together with the focusing lens group of the imaging lens system.

More specifically, in this auxiliary lens system, the first lens group is a biconvex lens or a composite lens of a concave meniscus lens and a biconvex lens, and the second lens group has a convex surface facing the object side. The single positive meniscus lens and the third lens group are negative meniscus lenses with a concave surface facing the image side, and it is desirable that the following fineness be satisfied.

0.2 <f12/f <0.5 ・-
...(1)0.1 <Ifs'/f <0.4.
f3<O... (2) 50 < 1ν11
(3) However, f: Focal length of the auxiliary lens system f12: Combined focal length of the first lens group and second lens group C1: If the first lens group is the previous lens, the corresponding lens If the first lens group is a composite lens, fl is its combined focal length, f1+, fl- are the focal lengths of the positive and negative lenses that make up the first lens group, and ν1+, ν1- are the focal lengths of the first lens group. When expressed as a number, the effective Atsube number □=-V-Goshi-1= ・−・・・・・・(4
)f ν1 f+V1 f+ −ν1
(Function) Figure 2 shows the refractive power arrangement of the conventional auxiliary lens system, which consists of two positive and negative lenses as described above, and the focal length f of the positive first lens group is used for focusing the imaging lens system. The focal length is set to be approximately equal to the focal length of the lens, and the negative second lens group provides the composite focal length f required for the function of the auxiliary lens system, but the drawback is that the overall length is long.

In this invention, as shown in FIG.
The lens group is a positive lens group, the third lens group is a negative lens group, and the first lens group is a positive lens group.
Keeping the focal length f1 of the lens group approximately equal to the focal length of the focusing lens group of the imaging lens system, the refractive power of the composite system of the two positive lens groups on the object side and the negative The refractive power can be strengthened, and thereby an optical system with a small telephoto ratio can be obtained.

The reason why the first lens group is made of a biconvex ridge lens or a bonded lens of a concave meniscus lens and a biconvex lens is to suppress fluctuations in olfactory color aberration, especially spherical aberration, caused by focusing. The shapes of the second lens group and the third lens group are meniscus shapes so that on-axis and off-axis light beams can easily enter each surface.
By suppressing the amount of comatic aberration generated on each surface, it is easy to correct aberrations of the entire system.

Conditions (1) and 9) are conditions for obtaining an auxiliary optical system with a short overall length with a simple configuration as in the present invention, and if the upper limit is exceeded, the refractive power of each group will be weak and the telephoto ratio will be large. turn into. If the lower limit is exceeded, it is advantageous for compactness, but it becomes difficult to correct aberrations. 〇Article PI: (3) is for correcting changes in chromatic aberration due to focusing, and if this range is exceeded, axial chromatic aberrations in particular changes become large.

(Examples) The present invention will be specifically described below with reference to the drawings.

FIG. 1 shows an example of a focusing device using the auxiliary lens system of the present invention, in which a focusing device having an auxiliary lens system 2 is disposed adjacent to an imaging lens system 1, which is a zoom lens. The focusing lens group 3 of the imaging lens system and the first group 4 of the auxiliary lens system, which have approximately the same focal length and point distance, are connected to each other and are
It unfolds as a body. A focus detecting element 6 is disposed at the focal position of the auxiliary lens system 2, and the focusing motor 5 is controlled and driven by its output signal. 7 is a driver for the focus detection element 6; 8 is a control device; when the auxiliary lens system 2 is focused on the focus detection element 6, the imaging lens system 1 is focused on the imaging surface 9; be done.

Examples of the auxiliary lens system are shown below. In the table, r is the curvature of the refractive surface, d is the distance between the refractive surfaces, n is the refractive index of the glass material, νd
indicates the Atsube number.

Example 1 Focal length f=50.1 High 7 degrees, f
B=25.7F number 4.0 d angle 2ω=6.8
゜i1= 39.455 a=o, 3s3f2=
28.111 = -13・933 7=-0,278f2= 1
7.701 Si1=-340.9 fl(g)=19.699 f1←)=-39,931 ν1←'= 6.0.7 Si1←'= 27.5 Example 2 Focal length m f =59.1 Back focus fB
=26.9F number 4.0 Angle of view 2ω=6.2°f+ = 39.427 -- 0.246f2
= 18.075 f3=-9,533 upper=-0,161 f+2= 14.542 Si1=-426.6 (-=ff Go〒+-1 Chi W) f1ν+ fl ν1 fl ν1f1...=
21.358 f, ('') = -47,388 Su (+) = 60.7 Tsu, (→= 25.4 Example 3 Focal length f = 54.5 Back focus fB =
26.3F number 4.0 Both angles 2ω = 5.8°f
2= 42.625 f+2= 20.690 ν1=fi4.1 Effects of the Invention As described above, this invention has a telephoto ratio of 0, 7 to 08 by using the simple table structure shown in FIGS. As shown in Figures 7 to 9, it was possible to obtain an auxiliary lens system with well-corrected aberrations while being extremely compact.

[Brief explanation of drawings]

FIG. 1 is an overall configuration diagram of a focusing device in which the auxiliary lens system of the present invention is used, FIGS. 6, 7, 8 and 9 are sectional views and aberration curve diagrams of Examples 1.2.3 of the auxiliary lens of the present invention, respectively. 1: Photographing lens system 2: Auxiliary lens system 3: 7 focusing lens group 4: Movable lens 5: Focusing motor 6: Focusing WJt output element 7: Element driver 8: Control device ft 9: Imaging surface patent applicant
Roku Konishi Photography Industry Administrative Agent, Patent Attorney, Sa
Fumi Fuji Male (2 others) 81El Figure ≠ 2 Nu I? L4 Diagram # 5 Diagram 6 Diagram call 7 Diagram F4 ω= 8.4 Liao
8 Fig. F4 ω = 2.9 Teruface double difference Astigmatism ω = 3,4 ω = 2.9 Non-day aberration

Claims (1)

[Claims] An auxiliary lens system having a focus detection element on its focal plane is separately provided for the imaging lens system, and a part of the auxiliary lens system is moved in conjunction with the focusing lens of the imaging lens system being extended for focusing. This is an auxiliary lens system for a focusing device that brings the auxiliary lens system into focus at the same time as the imaging lens by extending it out. a first lens group that moves in the direction; a fixed second lens group that has positive refractive power;
It has a three-group configuration with a fixed third lens group having negative refractive power, and the focal length f_1 of the first lens group is approximately equal to the focal length of the focusing lens group of the imaging lens system. An auxiliary lens system in which the first lens group is extended in unison with the focusing lens group of the imaging lens system.