JPS63247712A - Auxiliary lens system - Google Patents

Abstract

PURPOSE:To obtain the titled lens system which is compact and has the exit pupil position far from a focal plane by constituting an auxiliary optical system having 2 lens groups having positive and negative refracting powers successively from an object side in such a manner that said system satisfies the prescribed conditions. CONSTITUTION:The auxiliary lens system having a focus detecting element 7 at its focal plane is separately provided on a photographing lens system 1 and the auxiliary lens system is set at a focusing state by extending part 5 of the auxiliary lens system cooperatively with the extension of a focusing lens group 4 of the lens system 1 for the purpose of focusing. Said system consists, successively from the object side, of the movable 1st lens component having the positive refracting power and the stationary 2nd lens component having the negative refracting power. The 2nd component consists, successively from the object side, of a negative single lens and a positive single lens spaced therefrom. The 2nd lens component satisfies the conditions expressed by equation I and equation II. In equations, f1: the focal length of the 1st lens component, d2: the air spacing between the negative and positive lenses in the 2nd lens component, nuij: the Abbe number of the i-th lens material from the object side in the i-th lens component.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention provides a lens system for focus detection, in particular, a focusing lens of an imaging lens system, in which a part of the focusing lens is extended to achieve five in-focus states. The present invention relates to an auxiliary lens system for a focusing device that detects.

(Prior art) An auxiliary lens system having a focus detection element on its focal plane is separately provided to the imaging lens system, and when the focusing lens of the imaging lens system is extended for focusing,
A focusing device that sets an auxiliary lens system to a focused state by extending a portion of the auxiliary lens system is well known.

A conceptual diagram of its overall configuration is shown in Figure 1. Imaging lens system 1
An auxiliary focusing lens system is placed parallel to the lens.

A portion 5 of the auxiliary lens system 2 is extended in conjunction with a focusing lens group 4 driven by a focusing motor 3. A focus state is detected by a focus detection element 7 disposed at a position corresponding to the imaging cord 6.

In this type of focusing device, the pupil plane of the auxiliary lens system 2 is generally divided, and the light beams passing through each are used to control the element 7.
In a focusing device that detects focus by comparing images formed on a surface with each other, a shift in pupil position appears as a difference in the intensity of each image, which affects focusing accuracy. give.

Some of these focus detection systems have the exit pupil position of the auxiliary lens set relatively far away.For example, in Honeywell's TCL autofocus module,
The entrance pupil of the element is located 75+m forward from the element surface.

If the exit pupil of the auxiliary lens does not match this specified position,
It is known that focusing accuracy deteriorates.

In addition, even in a focusing device that detects the amount of blur on the focal plane, when a solid-state image sensor such as a COD is used as the focus detection element 7, if the distance between the color filter and the captured image is large, the auxiliary If the exit pupil of the lens system is close to the captured image, color shift occurs and distance measurement accuracy decreases.

Many conventional auxiliary lenses have problems with the exit pupil position when used in the above-mentioned focusing devices.

For example, the auxiliary lens system (Japanese Patent Application No. 61-26867) previously developed by the present inventors has a positive lens system for focusing that has a refractive power approximately equal to the focusing lens component of the photographing lens system, starting from the object side. Since it has a configuration of 1 lens group, a positive 2nd lens group, and a negative 3rd lens group, if the aperture is fixed to the 1st lens group, the exit pupil position will be close to the focal plane.To avoid this, If the diaphragm is placed away from the first lens group toward the object side, not only will extra lens barrel length be required to set the diaphragm, but it will also be necessary to maintain the luminous flux at the desired F number even around the light receiving element. Another possible method would be to place a new positive lens near the focal plane and move the exit pupil away from the object side, which would also increase the diameter of the auxiliary lens system.1. As for the auxiliary lens system as a whole,
A problem arises in that the number of lenses increases and the cost increases.

(Problems to be Solved by the Invention) The object of the invention is to create a compact auxiliary lens for a focusing device, in which the exit pupil position is far from the focal plane, without increasing the number of lens components compared to conventional lens systems. The purpose is to obtain a system.

(Means for Solving the Problem) In order to achieve the above object, in the present invention, an auxiliary lens system having a focus detection element on its focal plane is provided separately for the imaging lens system, and the focusing of the imaging lens system is In a focusing device that sets the auxiliary lens system to a focused state by extending a part of the auxiliary lens system in conjunction with the lens being extended for focusing, the auxiliary lens system used therein is As shown in Figure 2, its cross-sectional configuration is shown.

It consists of a first lens component that has a positive refractive power and moves in the optical axis direction for focusing in order from the object side, and a fixed second component that has a negative refractive power. It consists of, in order from the side, a negative single lens and a positive single lens placed with an appropriate air gap therebetween.

(Function) In this type of auxiliary lens system, the focus detection accuracy is generally better as the depth of field of the auxiliary lens system becomes shallower.In this invention, the refractive power of the second lens component is made negative. By making the entire system a telephoto type, the overall length of the lens system was kept short, the focal length was increased, and the depth of field was made shallow.

In addition, the second lens component is composed of a negative single lens in order from the object side and a positive m lens arranged with an appropriate air gap between the negative single lens and the positive m lens, which allows the exit pupil position to be sufficiently far away from the focus detection surface. It's for a reason.

(Example) Examples of this invention will be shown below.

Specifically, the configuration of the auxiliary lens system of the present invention is such that the first lens component is a doublet consisting of a negative lens and a positive lens, and the second lens component preferably satisfies the following conditions.

0.05<d, /f,<0.2...(1)1
<Sh2□/Sh□, <1.5... (2) However, f is the focal length of the first lens component, d2 is the air distance between the negative and positive lenses in the second lens component, and ν is the focal length of the first lens component. is the Abbe number of the j-th lens material from the object side in the i-th lens component.

Condition (1) is a condition for reducing the telephoto ratio while moving the exit pupil position further away; if the lower limit is exceeded, the telephoto ratio can be reduced, but the exit pupil position will become closer to the element.

If the upper limit is exceeded, the exit pupil position will move away, but the overall length will become longer.

Condition (2) relates to chromatic aberration, and when this lower limit is exceeded, the axial chromatic aberration becomes undersized in the second lens component having negative refractive power as a whole, making correction difficult. If the upper limit is exceeded, overcorrection will occur, resulting in excessive axial chromatic aberration.

In the following embodiments, the exit pupil position is the value when the diaphragm is placed in the first position. This position can be moved back or forth within a practical range.

In the table, r is the radius of curvature of each refracting surface, d is the interval between refracting surfaces, n,
is the refractive index, and ν is the Atsube number.

(Example 1) Focal length 111tf, 62.405 Both angles 2ω = 5
@28'F number 4.6 back focus f
fi=4.278 surface number r d nd
vd 1st 1 20.215 0.70 1
．． 75520 27.5 lenses 2 11.000 3
．． 40 1.65844 50.9 minutes 3 24
3.646 22.00 2nd 4 -2+, 875
0,80 1,51633 64. Run 5 14.
369 7.90 Zusei 6 63.381 1.60 1.71:11
00 53.9 minutes 7 -29.215 13.
00 cover 8 ool, 00 1.53280
70.2 Glass 9 ω The exit pupil is at a position of −73,7 from the detection element surface.

(Example 2) Focal length f = 62.394 Both angles 2ω = 5°28
'F number 4.6 Back focus f R=4
．． 315 page number r' d na
ν・1 1st 1 20.215 0.70 1.
75520 27.5 lenses 2 11.000 3.
40 1.658/14 50.9 minutes 3 24
3.646 22.20 2nd 4 -19.578
0.80 1. ．． 51633 64. Run 5 13
．． 625 7.10 Zusei 6 63.381 1.60 1,60311
60.7 minutes 7 -20.490 13.60
Cover 8 ool, 00 1.53280 70
．． 2 glass 9 o.

The exit pupil is located at -74,0 from the detection element surface.

(Effects of the Invention) As seen in each embodiment and drawing, the total length of the lens system from the first surface of the lens to the cover glass is sufficiently smaller than its focal length, and the exit pupil position is far away. Each aberration was well corrected, making it possible to obtain a lens system suitable as a focusing lens.

[Brief explanation of drawings]

FIG. 1 is a conceptual diagram of the entire focusing optical system implementing this invention.
FIG. 2 is a sectional view of the auxiliary lens system, and FIGS. 3 and 4 are aberration curve diagrams of Example L and Example 2. In the figure, the wl image lens system is 1, the auxiliary focusing lens system is 2, the focusing motor is 3, the photographing system focusing lens group is 4,
A part of the interlocking auxiliary lens system 2 is indicated by 5, an image sensor is indicated by 6, and a focus detection element is indicated by 7. Patent applicant Konishi Roku Photo Industry Co., Ltd. Applicant agent Fumio Sato (2 others) Figure 1 Figure 2 Figure 3 Spherical aberration Astigmatism Distortion Figure 4

Claims (1)

[Claims] For the imaging lens system, an auxiliary lens system having a focus detection element on its focal plane is separately provided, and the focusing lens of the imaging lens system is extended for focusing.
This is an auxiliary lens system used in a focusing device that sets the auxiliary lens system to a focused state by extending a part of the auxiliary lens system. It consists of a first lens component that moves in the optical axis direction and a fixed second component that has a negative refractive power. An auxiliary lens system characterized by consisting of a positive single lens arranged at