JPS59119545A - Out-of-focus detecting method - Google Patents

Abstract

PURPOSE:To detect an out-of-focus state with a high gain by applying photoelectric conversion to the light within a center region of the light transmitted through an objective, and to the light within a circular region around said center region, and detecting a relative position error between the focal point of the objective, and to the surface of a subject, from the relationship between the output signals of both regions. CONSTITUTION:The parallel luminous fluxes delivered from a light source 1 are reflected by a semitransparent mirror 2 and irradiated to a medium 4 via an objective lens 3, and this reflected light is sent to a photodetector 5 via the lens 3 and the mirror 2. The luminous intensity distribution on the detector 5 is symmetrical centering on an optical axis Z. The energy received at a circular photodetecting part PD2 is equal to the value E1 obtained by integrating the luminous intensity distribution covering from radius O through R1. While the energy of a circular photodetecting part PD1 is equal to the value E2 obtained by integrating the luminous intensity distribution ranging from radius R2 through R3. The luminous intensity distribution varies in accordance with the distance between the focal point F of the lens 3 and the surface of the medium 4, i.e., the out-of-focus degree (e). The output proportional to the value of (e) is obtained by calculating E1-E2. Thus an out-of-focus degree can be detected.

Description

DETAILED DESCRIPTION OF THE INVENTION (1) Technical Field of the Invention The present invention relates to a defocus detection method, and more particularly to a defocus detection method that utilizes the intensity distribution of light.

(2) Background of the technology Technical fields that require the focus of the objective lens in the optical system to be continuously or temporarily focused on the object plane, for example,
In the field of magneto-optical disk devices, various conventional means for performing such focus control are known.

However, each of these prior art means has its own technical problems that must be solved, and there is a demand for the development of technical means that can eliminate these problems.

(3) Prior art and problems Conventional defocus detection methods include a method in which a spherical and cylindrical lens is placed in the image space and the defocus is detected based on astigmatism in the image space, and a method in which the defocus is detected by astigmatism in the image space. There is a method in which a light beam is incident on an objective lens off-axis, and a focal shift is detected from the magnitude of the deflection of the reflected light within the image space.

The former of these methods has the disadvantage that its optical system is inevitably complicated, and
&fr, remove the optical axis of the objective lens and place it there.
・Since light is incident, the pupil diameter of the objective lens cannot be used effectively.

(4) Purpose of the Invention The present invention was devised in view of the drawbacks of the conventional method as described above.The purpose of the present invention is to simplify the optical system while at the same time achieving a focal shift that provides high detection gain. The object of the present invention is to provide a detection method.

(5) Structure of the invention The purpose of this invention is to photoelectrically convert the light in the central region of the light that is irradiated onto the object surface through the objective lens, reflected by the object surface, and transmitted through the objective lens to produce a first output. At the same time as obtaining fl, a second output signal is obtained by photoelectrically converting the light in an annular region surrounding the central region, and a predetermined relationship between the two output signals is determined from the focal point of the objective lens. This is achieved by detecting the relative value tif=iifl difference between and the object plane.

(6) Embodiments of the Invention The present invention will now be described in detail with reference to the accompanying drawings.

FIG. 1 shows one embodiment of the invention. In this figure, 1 is the light source, 2 is the semi-transparent mirror, 3 is the objective lens (H is the principal point on the image side, It" is the principal point on the object side), and F is the objective lens 3.
, 4 is a medium such as an optical disk, 5 is a photodetector, and Z is an optical axis.

As shown in FIG. 2, the center of the photodetector 5 is aligned with the Z axis (X
-Y intersection (direction perpendicular to the plane of the paper)) and has an annular light receiving portion PD1 with an outer diameter of ZR3 (radius R3) and an inner diameter of ZR2 (radius R2), and a diameter of ZRI (radius RI).
It consists of a circular light receiving portion PD2.

Next, the focus detection aspect of the configuration device described above will be explained.

The parallel beam of light emitted from light #; +f 1 is reflected by semi-transparent mirror 2,
The light is irradiated onto the medium 4 through the UJL and the objective lens 3, and the light reflected there passes through the objective lens 3 and the semi-transparent mirror 2 and reaches the photodetector 5.

The light intensity distribution on the photodetector 5 is axially symmetrical to the optical axis Z, as shown in FIG. 3, where r is the distance from the Z axis.

The energy received by the circular light receiving portion PD2 has a radius o
A value E1 is obtained by integrating the light intensity distribution from F to R1, and the energy received by the annular light receiving portion PDIO becomes a value E2 obtained by integrating the light intensity distribution from half f-IR2 to R3.

However, the intensity distribution of the light reaching PI) 1 and PO2 is determined by the distance 1ζ1 between the focal point F of the objective lens 3 and the surface of the medium 4.
1, and let the amount of defocus be e, it changes as shown in (4, -1) in FIG. 4 depending on the value of e. (Jl, and e takes the positive direction in which the medium 4 moves from the focal point F in the direction opposite to the objective lens 3. (4-2) in FIG. 4 shows the optical path corresponding to (4-1).

When the light intensity distribution changes like this, PDl and PO2
The energy received also changes.

For example, when a < Q, the energy E2 received by PO2 decreases, and the energy E1 received by PDIO LJ relatively increases.

Also, in ego, if the absolute value of e is relatively small, R
2 increases and El decreases.

Therefore, by performing the calculation El-R2, it is possible to obtain an output proportional to the value of e, so that defocus can be detected.

Figure 5 shows the spot size ZR of the incident luminous flux, the diameter (g53) where the intensity of the intensity distribution is 1/e2 of its central intensity
(See figure)), the above radius R1, R2, 3 is R1=0.6RE R2=o, 6R.

R3=2.4R.

In the case of (El-R2)-e curve diagram, its A
This range indicates good detection system characteristics.

FIG. 6 shows the main part of another embodiment of the present invention.

In this embodiment, instead of the photodetector 5 having the annular light receiving part PD■ and the circular light receiving part PD2 in the embodiment shown in FIG. “S7+
This embodiment is different from the embodiment shown in FIG. 1 in that 8 is provided. Then, set the outer diameter of the photodetector 7 to the circular light-receiving part P I) in Fig. 1.
By making the outer diameter ZRI of 2 and the hole diameter of the reflecting mirror equal, and the outer diameter ZR3 of the annular photoreceptor PD in FIG. is obtained. This embodiment has the advantage that the photodetector does not require a multi-dimensional light receiving surface.

FIG. 7 shows the main part of yet another embodiment of the present invention.

In this embodiment, the circular light receiving part PD2 of the embodiment in FIG. 1 is divided into four parts (PD21, PD22, PD2 4°3, P
l, ) 24) This embodiment differs from the embodiment shown in FIG. 1 in this respect. This includes divisions (other than four divisions) of this circular light-receiving section.

), it is possible to detect the position of the object plane in a plane perpendicular to the optical axis of the object. This is achieved by detecting the intensity distribution of the second image of the object on the photodetector 5'' with four light receiving sections and calculating the output thereof.

In the above embodiment, an example in which each light receiving section is formed in a circular shape has been described, but it may be formed in another shape, for example, a polygon. Further, in these cases, the center of the detection system is set on the optical axis, but there may be a deviation between the two within an allowable degree of closure.

(7) Effects of the Invention As is clear from the above description, the present invention has the following effects: (1) simplifying the optical system, (2) effectively utilizing the luminous flux, and (2) obtaining high detection gain. You can get rid of it.

[Brief explanation of drawings]

1 is an IRI showing one embodiment of the present invention, FIG. 2 is a front view of the photodetector of the embodiment shown in FIG. 1, FIG. 3 is a diagram showing the photodetector and light intensity distribution, and FIG. The figure shows the light intensity distribution and the optical path in the optical system for a defocus bond, and Figure 5 shows (El-
22) is a graph showing the relationship between FIG. In the figure, [ is a light source, 2 is a semi-transparent mirror, 3 is an objective lens, and 5 is a photodetector.

Claims (4)

[Claims] (1) Charge and convert the light in the central region of the light that is irradiated to the object surface through the objective lens, reflected by the object surface, and transmitted through the object lens to obtain the first output signal. ,
The light in the annular area surrounding the central area is photoelectrically converted into a second
A method for detecting defocus, comprising: obtaining an output signal, and detecting a relative position error between the focus of the objective lens and the object surface from a predetermined relationship between the two output signals "i" and "n1". (2) Defocus detection according to claim 1, characterized in that the central region is a circular region, the annular region is an annular region, and the center of these regions is set to the optical axis of the objective lens. Method. (3) The light in the circular area is the light that has passed through the hole of the annular reflector, and the light in the annular area is the light reflected from the annular reflector. The defocus detection method described in Section 2. (4) The circular area is divided into a predetermined number of parts, and the light from each divided area is photoelectrically converted and provided in the predetermined relationship. The defocus detection method according to item 3.