Radiant energy – Photocells; circuits and apparatus – Photocell controls its own optical systems
Patent
1992-11-30
1993-09-14
Nelms, David C.
Radiant energy
Photocells; circuits and apparatus
Photocell controls its own optical systems
2502017, G01J 120
Patent
active
052451739
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
This invention relates to an in-focus sensing apparatus of optical equipment, such as a microscope, that allows observation in a wide range from low to high magnifications.
In connection with an apparatus that senses the optical images before and after the image formation plane with the image sensor, and adjusts the distance between the objective optical system and specimen so that the difference between the electric signals corresponding to the light intensities of those two optical images may be kept at a specified value, Published Examined Japanese Patent Application No. 61-60413 has disclosed a focal-point adjusting apparatus provided with means for varying the optical path between the image formation plane and image sensor as the magnification of the objective optical system is changed.
Additionally, Published Unexamined Japanese Patent Application No. 63-78113 has disclosed an automatic focal-point adjusting mechanism which divides the measuring light beam going from the subject to the line sensor into a plurality of light beams, shifts the light formation positions of the divided light beams forward and backward along the optical axis, performs the in-focus operation by comparing the signals of two optical images, and enables a high regular-transmission transparent member whose refractive index differs from that of air to withdraw into one of the divided light beams during the time from when the measuring light beam has been divided until the light beams reach the line sensor, in the optical path of the measuring light beam.
The method of projecting the optical images before and after the expected focal plane onto the image sensor and comparing the signals of two optical images to sense the in-focus point has a disadvantage in that use of a high-magnification objective makes the difference between the signals of two optical images before and after the expected focal plane so small that the in-focus point cannot be sensed. To solve this problem, a method has been proposed which is capable of changing the difference in the optical path between the expected focal plane and image sensor according to the change of the magnification of the optical system, such as the change of objectives, and which makes the optical path difference greater in the case of high magnification, as disclosed in Published Examined Japanese Patent Application No. 61-60413. This method, however, has disadvantages in that the large optical path difference necessary for high magnification makes the optical path space larger, consequently the apparatus greater, and that an arrangement to change the optical path difference is needed.
Another disadvantage is that at high magnification, since the optical image is divided into two optical images in spite of the amount of light of the original optical image is very small, the amount of light of the resulting images is even smaller, which makes the sensing of the in-focus point difficult.
SUMMARY OF INVENTION
Accordingly, the object of the present invention is to provide an automatic focal-point sensing apparatus capable of sensing the in-focus point with high accuracy in the range from low to high magnifications.
The foregoing object is accomplished by providing an automatic focal-point sensing apparatus comprising:
a lighting optical system for illuminating a specimen;
an objective optical system which receives the optical image from said specimen illuminated by said lighting optical system, and which forms a first optical image at a position a specified distance apart from and before the expected image formation plane and a second optical image at a position a specified distance apart from and after the expected image formation plane;
at least one image sensor which has a first and a second light-receiving sections that receive said first and second optical images from said objective optical system, and which converts said first and second optical images received into corresponding electric signals;
magnification sensing means for detecting the magnifica
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patent: 4587416 (1986-05-01), Kudo et al.
patent: 4621191 (1986-11-01), Suzuki et al.
patent: 4803352 (1989-02-01), Bierleutzeb
Konishi Hirokazu
Nagasawa Nobuyuki
Takahama Yasuteru
Yamana Motokazu
Allen S. B.
Nelms David C.
Olympus Optical Co,. Ltd.
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