Television – Camera – system and detail – Optics
Reexamination Certificate
1999-08-25
2004-03-02
Vu, Ngoc-Yen (Department: 2612)
Television
Camera, system and detail
Optics
C348S340000, C348S357000, C348S374000, C396S358000
Reexamination Certificate
active
06700617
ABSTRACT:
The present invention claims priorities of Japanese Patent Applications Serial Nos. H10-248793 and H10-272000, the contents of which is incorporated hereinto by reference in its entirety.
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to an image taking apparatus such as a digital camera.
2. Description of the Related Art
As a silver-halide camera, a single-lense reflex camera equipped with an interchangeable photographing lens is known. As shown in
FIGS. 8 and 9
, the silver-halide single-lense reflex camera is comprised of a box-shape camera main body
202
and a photographing lens
204
interchangeably attached to a front surface of the camera main body
202
via a mounting portion
203
.
In the camera main body
202
, a film
206
is installed at a rear portion of the main camera body
202
so as to be positioned on a focal point of the lens unit
205
of the photographing lens
204
. A focal plane shutter
207
is provided in close proximity to the front of the film
206
. In front of the focal plane shutter
207
, a quick return mirror
209
is provided. The quick return mirror is pivoted by a pivot shaft
208
to change the position between an up-position and a down-position. Also provided in the camera main body
202
is an AF (Automatic Focussing) sensor
210
for receiving an optical image of an object passed through the lens unit
205
to detect the focussing status of the optical image formed on an image focussing surface of the film
206
.
Above the quick return mirror
209
, a focussing screen
211
for reproducing the focussed image formed on the image focussing surface of the film
206
is provided so as to be located in a plane equivalent to the image focussing surface. Provided on the camera main body
202
is a penta-finder
212
including a penta-prism
214
for reflexing the optical image of the object focussed on the focussing screen
211
to a rear ocular
213
. Furthermore, a light sensor
215
for measuring the luminance of the object is equipped in the finder
212
.
In the silver-halide single-lense reflex camera, as illustrated by the actual line in
FIG. 8
, the quick return mirror
209
is normally positioned such that the pivotal end (i.e., upper end) of the mirror
209
is positioned near the upper portion of the film
206
and the opposite end (i.e., lower end) thereof is located near the photographing lens
204
so as to be inclined by 45 degrees to the light axis. Depressing the shutter button
216
causes the quick return mirror
209
to rotate about the pivot shaft
208
in the direction of the arrow to the horizontal position indicated by the imaginary line in FIG.
8
. Then, the focal plane shutter
207
opens, which in turn causes the object image confirmed through the finder
212
to be focussed onto and recorded by the film
206
.
In the meantime, with the progress of the semiconductor technology, a digital camera in which an image pick up element such as a CCD (Charged Coupled Device) is used in place of the film
206
, has been spreading recently. In such a digital camera, the image pick up element photoelectrically converts an optical image of an object into electric signals, which are then subjected to image processing to generate image data. The image data is recorded in a recording medium, such as a memory card, or is reproduced on a display of a camera main body or a personal computer.
While the use of digital cameras have spread widely, it has been proposed to make the maximum use of the resources of a silver halide camera. In other words, a digital camera utilizing a camera main body
202
and a photographing lens
204
of a silver-halide single-lens reflex camera, has been proposed. In such a digital camera, an image pick up element, such as a CCD, is generally provided at a film position (lens back position) to receive an optical image of an object focussed by the photographing lens
204
when the quick return mirror
209
is upwardly moved by fully depressing the shutter button
204
.
The light receiving surface of the image pick up element in such a digital camera is generally covered by a protection glass layer. In addition, the pixels constituting the image pick up element are regularly arranged. Therefore, if the image pick up element is utilized as it is, influences of return noises cannot be avoided. To prevent such noises, an optical low pass filter is generally disposed on the front surface of the image pick up element.
Since for a silver-halide single-lens reflex camera the thickness of the film
206
is several tens microns, a required depth from the image focussing surface for installing the film
206
is slightly larger than several tens microns. Accordingly, a silver-halide single-lens reflex camera is designed to have such a depth.
In a digital camera, the image pick up element and the optical low pass filter are large in thickness. Especially, the optical low pass filter is relatively thick. Therefore, it is very hard to install the optical low pass filter in a narrow limited space between the image pick up element and the quick return mirror
209
.
So long as the camera main body of the silver-halide single-lens reflex camera is utilized, it is impossible to change the distance from the mounting portion
203
to the image focussing surface. Furthermore, the location of the quick return mirror
209
cannot be changed because the focussing status on the image focussing surface should be reproduced on the focussing screen
211
.
Therefore, if an image pick-up unit including the image pick up element and the optical low pass filter is positioned on an appropriate portion, a mechanical interference may occur between the quick return mirror
209
and the image pick-up unit. Such a mechanical interference may cause a damage of the quick return mirror
209
or a shift of the image pick up element which in turn causes an out-of-focus.
The focal plane shutter
207
can be removed because the image pick up element itself has a function for controlling the exposure start and terminate timing (electronic shutter function). However, removing the quick return mirror
209
causes a big mechanical change, which eliminates the effective use of the resources of a silver halide single-lens reflex camera.
To avoid the mechanical interference as mentioned above, it has been proposed to utilize a thin optical low pass filter. However, thinning the filter causes a deterioration of the filtering function, which in turn deteriorates the quality of the image to be obtained.
Another proposal for solving the above mentioned problems is to dispose an optical low pass filter around the lens mounting portion
203
in front of the quick return mirror
209
. However, this will arise such a problem that some photographing lenses cannot be used because rear lenses thereof comes into contact with the optical low pass filter.
Furthermore, an infrared cutting filter is sometimes mounted in front of the image pick up element to solve the luminosity difference between the image pick up element and the human's eyes. In this case, however, the similar problems as in the optical low pass filter will also arise.
SUMMARY OF THE INVENTION
Therefore, it is an object of the present invention to provide an image taking apparatus which can prevent a mechanical interference between an image pick up unit for picking up an optical image passed through an image taking lens and a mirror which is capable of changing a position thereof between, one being on an optical path of the image taking lens and the other being off the optical path.
It is another object of the present invention to provide an image taking apparatus which can effectively prevent a damage of the mirror and an occurrence of out-of-focus, and allow a wide selection of an image taking lens.
According to one aspect of the present invention, an image taking apparatus includes an image taking lens, a mirror which is capable of a pivotal movement such that the mirror changes a position thereof between a first position where the mirror is disposed on an optical path o
Hamamura Toshihiro
Kubo Hiroaki
Minolta Co. , Ltd.
Sidley Austin Brown & Wood LLP
Vu Ngoc-Yen
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