JPS5916246B2 - Focus position detection method using lens chromatic aberration - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for detecting a focus position using chromatic aberration of a lens.

In recent years, camera automation has progressed significantly, to the extent that only the automation of pit alignment, that is, the realization of autofocusing, remains as a challenge.

However, although various proposals have been made regarding this autofocusing, at present they are only a step away from actualization, some require expensive equipment, and some have problems with accuracy. It was problematic. The purpose of the present invention is to solve the above-mentioned problems in autofocusing by providing a simple and accurate method for detecting the in-focus position by utilizing the chromatic aberration of the lens, and thereby to further improve the performance of the camera. Automation, etc.

In general, lenses have some chromatic aberration, not only when used alone, but also when they are achromatized in combination.As a result, light rays originating from the same object point and incident on the same point on the lens, after refraction, Its path differs somewhat depending on the wavelength.

Therefore, the image point position also differs slightly depending on the wavelength. The present invention aims to provide a method for easily and accurately detecting the in-focus position by effectively utilizing such characteristics, which are also disadvantages of lenses. Hereinafter, the present invention will be specifically explained based on illustrated embodiments.

In Figure 1, an incident light beam passes through an objective lens 1 (hereinafter collectively referred to as an objective lens) of a camera's photographing lens or other optical equipment, etc. from the left to the right. On the optical path to the right of the objective lens 1, there is a semi-transparent reflecting mirror 2 inclined by 450 degrees with respect to the optical axis of the objective lens 051 so as to reflect a part of the light beam upward. It is located.

On the optical path of the light beam that has passed through the translucent reflector 2, a red light beam (with a wavelength of approximately 6
A light-receiving element 4 having a light-receiving surface 4a on which light (00 to j0700 nm) is incident is disposed. On the other hand, the light beam reflected upward by the semi-transparent reflector 2 passes through the blue light transmitting filter 5 on the optical path when the objective lens 1 is focused. A light-receiving element 6 having a light-receiving surface 6a on which a blue light beam (wavelength of approximately 400 to 500 nm) enters is disposed. In the present invention, the translucent reflecting mirror 2, the red light transmitting filter 13, and the blue light transmitting filter 15 constitute a spectroscopic means that separates two types of light beams of different wavelengths from the light beam passing through the objective lens 1. This can be easily replaced with a well-known one.

Further, both the light receiving elements 4 and 6 have a nonlinear CdS. It is made of a photoconductive or photovoltaic element made of Se, Si, etc., and transmits two types of light beams from the center 2a of the semi-transparent reflecting mirror 2 to the light receiving surfaces 4a of both light receiving elements 4, 6.
The optical path lengths reaching 6a are determined to be equal to each other. That is, both the light receiving elements 4 and 6 are arranged at mutually conjugate positions with respect to the objective lens 1. Illumination coefficient K
It is known that in a nonlinear light receiving element such as +1, the photoresistance value or photoelectromotive force becomes the smallest value but the largest value when the pit is aligned with the light receiving surface. In other words, when the objective lens 1 is shifted along its optical axis to focus, the output changes of the two light receiving elements 4 and 6 described above are as shown by the photocurrent curves 1R and 13, respectively, in FIG. 2, for example. , the position Pl where each of the two light beams exactly forms an image,
It changes greatly in the vicinity of P2, and this position Pl, P2
shows an extreme value at . In the present invention, the point PO between the two extreme values of the output changes of both the light receiving elements 4 and 6 that occurs in this way is the point where the two outputs are equal, that is, the intersection point PO of both curves R and IB.
is detected, and this is set as the focal position of the objective lens 1.

In this way, first, after detecting the extreme value of one light receiving element 4, if a point where the outputs of both light receiving elements 4 and 5 are equal is detected, this means that the objective lens 1 is focused from the front. In addition, if, contrary to the above, a point where both light receiving elements 4 and 6 are equal is detected after the extreme value of light receiving element 6 is detected, this means that objective lens 1 is focused from behind. This shows whether the pin was a front pin or a rear pin. In any case, in the present invention, if the extreme value of either one of the light receiving elements 4, 6 is detected, then using this as a guide, the next point P
Since O can be the focal position of the objective lens 1,
Pit alignment can be performed extremely easily and accurately. Incidentally, the change in the output of both the light receiving elements 4 and 6 can be easily automatically measured by setting a reference level in advance and comparing it with the output of the pixel element. In the present invention,
Combinations of light fluxes of different wavelengths that are incident on the light receiving element include the combination of red light and blue light shown in the above example, as well as
By any monochromatic light or multiple combinations of bichromatic light,
This can be replaced.

[Brief explanation of the drawing]

FIG. 1 is a side sectional view showing an example of a lens focusing position detection device used in carrying out the method of the present invention, and FIG.
FIG. 3 is a photocurrent curve diagram showing a change in the output of a light-receiving element due to focusing in the method of the present invention. 1... Objective lens, 2... Semi-transparent reflecting mirror, 3, 5... Filter 1, 4, 6...
·Light receiving element.

Claims (1)

[Claims] 1. Of the light that has passed through the objective lens, it is split into two types of light beams with different wavelengths by a spectroscopic means, and the illuminance coefficient K≠1 is applied to the planned focal plane of the objective lens in the paths of the split beams. A nonlinear light receiving element made of a semiconductor having a characteristic that the output shows an extreme value when focused is arranged respectively, and the separated light beams are incident on each of the pair of nonlinear light receiving elements, and due to the chromatic aberration of the objective lens, both light beams are separated. Based on the fact that the image formation positions on the nonlinear light receiving element are different, when the objective lens is focused, the point at which the outputs of both of the nonlinear light receiving elements coincide between the extreme values of the respective outputs of the two nonlinear light receiving elements. A method for detecting a focus position based on chromatic aberration of a lens, the method comprising detecting the chromatic aberration of a lens and setting this as the focus position.