Photography – With exposure objective focusing means – focusing aid – or... – Optical detail with photoelement system
Reexamination Certificate
2000-09-28
2003-04-15
Adams, Russell (Department: 2851)
Photography
With exposure objective focusing means, focusing aid, or...
Optical detail with photoelement system
C359S290000, C359S291000
Reexamination Certificate
active
06549730
ABSTRACT:
This application is based upon application No. 11-276442 filed in Japan, the contents of which are hereby incorporated by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a spatial modulation unit, a luminous flux deflection device, a focus detection device, a camera and a focus control device, which are capable of changing the focal position.
2. Description of the Related Arts
Conventionally, there have been known a plastic mold Fresnel plate, a photographic dry plate type diffraction grating, a glass plate marking-off type diffraction grating, a photographic dry plate type hologram and a photoresist type hologram, in each of which the transmission or reflection optical path is fixed in the manufacturing stage.
As a technique for deflecting the transmission or reflection optical path, there are, for example, the following techniques.
In Japanese Non-examined Laid-open Patent Publication No. 10-62609, there is disclosed a microlens capable of adjusting the focal position. The microlens is constituted by a single lens by itself, can change the focal position thereof and is applicable only to a lens with a small-diameter pupil. If the microlens is simply increased in dimension, then the necessary spherical surface (aspherical surface) cannot be obtained, meaning that the practicality is presumably difficult. The disclosed microlens is intended to constitute an image-forming optical system of an imaging device and has neither effect nor construction for preventing the pupil shading caused by the imaging lens.
In Japanese Non-examined Laid-open Patent Publication No. 9-184965, there is disclosed a technique for providing the deflector for deflecting the incident optical path with a power. However, the lens power is not changed, and the pupil of the imaging lens cannot be effectively used.
Also, a technique capable of forming a microlens array and changing the focal position has been known. However, only a lens having a diameter of several tens to several hundreds of micrometers can be formed.
For example,
FIGS. 18 and 19
show a conventional liquid crystal cell. There are proposed a prism element capable of varying the deflection angle and a lens capable of varying the focal position, by using liquid crystals that exhibit an anisotropic electrooptical characteristics. Namely, the molecular alignment state of liquid crystals are controlled.
FIG. 18
is a view of a liquid crystal cell constructed of nematic liquid crystals
401
. The reference numerals
410
and
411
denote circular hole pattern electrodes, across which a voltage V is applied. An equipotential surface in this case is indicated by the wavy lines in FIG.
18
.
Then, a plurality of cells of
FIG. 18
are assembled to form the structure of FIG.
19
. The structure includes a liquid crystal layer
401
for generating a refraction power, alignment films
404
and
405
and glass substrates
402
and
403
. The reason why the alignment films are coated is to align the liquid crystal molecules in one direction by performing a rubbing process. Holes
410
a
and
411
a
of the circular hole pattern electrodes
410
and
411
become the respective lenses.
If a voltage not lower than the threshold value is applied to the liquid crystal cell, then there is obtained a liquid crystal alignment state determined depending on the alignment regulation force of the substrate, the elasticity force of the liquid crystals and the alignment force caused by the electric field. This state is shown in FIG.
18
. The inclination of alignment varies depending on the distance from each electrode. The refractive index is small near the electrodes, and the refractive index is great at the center of the circular hole. With this arrangement, a characteristic similar to that of a convex lens can be obtained.
Conventionally, one cell has a diameter size of 300 &mgr;m and a liquid crystal thickness of 100 &mgr;m, and the application voltage has about 1 to 5 V. The effective region has a very small region and is intended, for example, for condensing the laser light beam to about 2 &mgr;m. Namely, it is impossible to use the effective region in a size that can be expressed on the order of millimeters.
Also, a diffraction grating capable of changing the optical path is known. However, this is not constructed by itself so as to have a focal position.
Also, a display device whose optical path is changed by a micro-mirror is known. This device is intended to spread a point light source into a wide range for display and is not constructed only by itself so as to obtain a focus. If it is tried to obtain a focus by this device, then unevenness will presumably result in since the arrangement is a square arrangement.
With regard to an incident luminous flux deflecting device to be utilized for a sensing device for sensing the focus of an optical device or the like, the following techniques have conventionally been known.
For example, in Japanese Non-examined Laid-open Patent Publication No. 10-62681, there is disclosed a technique for varying a shielding means by the open f value of the imaging lens inside the sensing unit. However, the lens power is not changed, and the position of the shielding portion moves (baseline length is varied) to disadvantageously change the sensing accuracy.
In Japanese Non-examined Laid-open Patent Publication No. 58-78101, there is disclosed a technique for setting the power of the field lens arranged in the vicinity of the focal plane of the imaging lens so that the image of the image-forming lens falls within the exit pupil. However, there is achieved no change according to the pupil position and diameter of the imaging lens.
In Japanese Non-examined Laid-open Utility Model Publication No. 55-155223, there is disclosed a technique for changing a shielding means symmetrical about the optical axis inside the sensing unit according to the mounting/dismounting of the focalplane plate. However, the lens power is not changed, and the shielding portion is moved. Furthermore, the necessary quantity of light cannot be obtained.
As described above, in the Japanese Non-examined Laid-open Patent Publication No. 9-184965, there is disclosed a technique for providing a deflection means for deflecting the incident optical path with a power. However, the lens power is not changed, and the pupil of the imaging lens cannot be effectively used.
When executing a sensing operation for the purpose of imaging and measurement by utilizing the luminous flux from the subject, which has been incident on the object lens and passed through the pupil of the object lens, in general, the luminous flux should preferably be utilized within the full span of the exit pupil of the lens taking the sensing range (area) and accuracy into consideration.
However, when executing a focus detecting operation by means of, for example, a camera, then the position and size of the exit pupil differs depending on the type of the imaging lens, or the object lens, and the pupil position and size are changed by focusing and zooming even with an identical imaging lens. Conventionally, the optical path is fixed, and therefore, the optical path is designed according to the type of the imaging lens and the possible minimum size of the exit pupil when focusing or zooming operation is executed. Based upon the above reasons, there have been limitations on an improvement in accuracy and on the widening of the focus area using an area sensor.
Namely, with regard to the focus detection accuracy, a higher accuracy can be obtained when a wider exit pupil region is used. The accuracy is determined depending on the distance between the two rays of luminous flux that form the two subject images from the optical axis of the imaging lens. The greater the distance between the rays of luminous flux in the exit pupil position, the higher the accuracy is. If the focus detection area is set wide, then the center of the luminous flux comes closer to the optical axis due to the wideness of the area. In order to increase the accuracy and widen the area, it
Adams Russell
Burns Doane , Swecker, Mathis LLP
Minolta Co. , Ltd.
Smith Arthur A
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