Parallax error prevention between a zoom lens and an optical finder of an electronic camera

Abstract: An electronic camera (1) having an image sensor (4) to receive the rays of an object (10) and convert them into the electrical image signals comprises an optical finder (3) capable of varying its enlarging magnification or photographing area; reading means (5) to read the signals of a part of the area of the image the rays of which are received by the image sensor; and reading area modifying means to modify the size of the area thereby to read the signals from the image sensor in accordance with the enlarging magnification of the finder or the displayed photographing area. Further, such an electronic camera comprises metering means (7) to measure the distance between an object and the taking lens (62), and the foregoing reading area modifying means modifies the size and position of the area thereby to read the signals from the image sensor in accordance with the finder magnification or the displayed photographing area and the measured value by the metering means. This prevents from the parallax phenomenon between the zoom lens and the optical finder.

Description: The present invention relates to an electronic camera having an image sensor according to the pre-characterizing part of claim 1. Related Background Art The structure of a conventional electronic camera of the kind is shown in Fig. 6. The conventional electronic camera 61 comprises a zoom lens 62 which is an image magnification variable taking lens, an optical zoom finder 3 of a variable enlarging magnification type, an image sensor 4 to receive the rays from an object and convert them into electrical image signals, a recording medium 6 to record the foregoing image signals, a metering device 7 to measure the distance between the object and the camera, a zooming lever 8 to vary the image magnification of the zoom lens 62 and the enlarging magnification of the zoom finder 3, and a control device 5 as shown in Fig. 6. In this respect, reference numeral 10 designates an object and 11, a photographer. The conventional electronic camera 61 thus structured performs its photographing operations set forth below. In other words, the photographer 11 observes the object 10 through the zoom finder to operate the zooming lever 8 to set a desired image magnification. When the zooming lever 8 is held down to the left in Fig. 6, a switch SW1 is turned on. The zoom finder 3 is driven by a driving device which is not shown to shift a member 3a of its optical system thereby to enlarge the object image in a given frame of a field. Hence, the enlarging magnification is increased. At this juncture, a member 62a of the optical system in the zoom lens 62 is interlocked with the zooming operation of the foregoing finder 3. It is thus shifted to cause its image magnification to be increased in proportion to the image magnification of the zoom finder 3. The size of the object image occupying the light receiving area of the limited image sensor 4 is increased accordingly. On the other hand, when the zooming lever 8 is held down to the right in Fig. 6, a switch SW2 is turned on. The zoom finder is driven by a driving device which is not shown to shift a member 3a of its optical system in the direction opposite to the foregoing operation thereby to reduce the enlarging magnification of the zoom finder 3. At the same time, the member 62a of the optical system in the zoom lens 62 is interlocked with this operation. It is thus shifted to decrease its image magnification in proportion to the image magnification of the zoom finder 3. As described above, the operation is performed so that the ratio between the object image observed by the photographer 11 through the finder 3 and the field frame, and the ratio between the object image projected on the image sensor 4 and the light receiving area of the image sensor can be equal. Then, when the photographer depresses a release button (not shown), a metering device 7 is caused to measure the distance between the camera and the object. A member of the optical system of the zoom lens 62 is driven by a driving device which is not shown in accordance with such a measured value to allow the object image to be imaged on the image sensor 4. Thus, the image information on the foregoing image sensor 4 is recorded on a recording medium 6. Further, Fig. 7 and Figs. 8A and 8B are views showing another example of a prior art. As shown in Fig. 7, this electronic camera 71 comprises a taking lens 72, a finder CRT 73, an image sensor 4, a control device 5, a recording medium 6, a metering device 7, a zooming lever 8, and an image memory 9. In this respect, a reference numeral 10 designates an object, and 11 a photographer. Also, Fig. 8A illustrates an image displayed on the finder CRT. Fig. 8B illustrates an image formed on the image sensor 4. Here, the image B formed on the image sensor is reversed due to the optical effect of the taking lens. To describe the photographing operation of this electronic camera, when the photographer turns on a power source of the camera by a power source switch which is not shown, the distance between the camera and the object is measured by the metering device 7. Then, in accordance with the metered information a member 72b of the optical system of the taking lens 72 is driven by a driving device which is not shown to enable the object image to be focused on the image sensor 4. The image sensor 4 converts the optical information into electrical signals to record them in the image memory 9. The signals inputted into the image memory 9 are read to be displayed on a finder CRT 73. The photographer 11 observes the object image displayed on the finder CRT 73 and operates the zooming lever 8 to set a desired photographing magnification. When this zooming lever 8 is held down to the left in Fig. 7, a switch SW1 is turned on, and while referring to the images shown in Figs. 8A and 8B, an area C in the image B formed on the image sensor 4 is enlarged by the image memory. This enlarged image is displayed on the finder CRT 73. Then, the foregoing area C is further narrowed by the operation of the zooming lever 8. In other words, it is possible to increase the enlarging magnification still more. On the other hand, when the zooming lever 8 is held down to the right in Fig. 7, a switch SW2 is turned on. Then, the area C shown in Fig. 8B is enlarged to an area designated by a reference mark B. The photographing magnification becomes small, and this image is displayed on the finder CRT 73. This electronic camera 71 according to the prior art is capable of varying the enlarging magnification of an object electrically with the operations described above, and when a release button which is not shown is depressed, the control device 5 is driven to record the image displayed on the finder CRT 73 in the recording medium 6. However, in the conventional electronic cameras described above, the problems are encountered as set forth below. In other words, in the electronic camera 61 shown in Fig. 6, it is required to mechanically interlock and drive the two optical members having different shifting distance, namely, the optical member 62a in the zoom lens 62 and the optical member 3a in the zoom finder 3. Thus, there is a problem that the mechanism of the camera becomes inevitably complicated. Furthermore, if the photographing magnification is great and the distance to an object is short, the socalled parallax occurs. This is a phenomenon that a deviation takes place between an object visualized in a finder and the actual object to be photographed. This phenomenon is caused by a deviation between the optical center of a zoom lens and the optical center of a zoom finder. With reference to Fig. 6 and Fig. 7, this phenomenon will be described. As shown in Fig. 6, there is an object 10 on the extension of the optical axis P1 of the zoom finder 3. Therefore, the object 10 is observed in the center of the zoom finder 3. However, since no object is present on the optical axis Q of the zoom lens 62, the object 10 is not imaged in the center of the image sensor 4 but is imaged in a position away from the center of the image sensor by a distance x. As a result, any image taken by this camera 61 differs from the image desired by the photographer 11 when visualized through the finder 3. On the other hand, in the conventional electronic camera shown in Fig. 7, there is no need for the two optical members, the zoom lens and Zoom finder, to be interlocked when driven as shown in Fig. 6. Also, no deviation takes place between the optical axis of the finder and the optical axis of the taking lens. There is no possibility that any parallax is generated at all. Nevertheless, in the foregoing electronic camera, the finder CRT 73 and image sensor 4 are constantly energized while the photographer 11 observes the finder 73. Consequently, it is necessary to provide a cell of a large capacity; not only making it necessary to make the camera large, but also to increase the manufacturing cost of the camera due to the provision of the aforesaid CRT 73. DE-A-39 21 983 discloses a compound camera based on a conventional optical camera and an electronic camera, the conventional optical camera being used for high quality imaging, the electronic camera being used to monitor imaging conditions of the optical camera. Parallax correction is obtained by making the image field of the electronic camera to completely include that one of the optical camera, the greater image of the electronic camera being reduced to the image of the optical camera by electronic means. Patent Abstracts of Japan, vol. 12, No. 385 (E-668), 14/10/88 & JP-A-63 128 879 discloses a means for parallax correction between an optical finder system and an image sensor of an electronic camera. The present invention is designed with a view to solving the above-mentioned problems in the conventional electronic cameras. It is an object of the invention to provide a small electronic camera of a simple structure which consumes only a small power but not generates any parallax. According to the present invention, there is provided an electronic camera having the features of claim 1. The aforesaid observation area modifying means comprises a finder magnification modifying means which modifies the area to be photographed by changing the enlarging magnification of the foregoing optical finder. The aforesaid reading area modifying means is capable of modifying the size of the area to be read from the foregoing image sensor in accordance with the enlarging magnification by the foregoing finder magnification modifying means. Further, an electronic camera according to the present invention is provided with a taking lens to image the foregoing object image on the foregoing image sensor, and a metering means for measuring the distance between the electronic camera and the object, and the foregoing reading area modifying means is capable of modifying the size and position of the area from which to read out the signals of the foregoing image sensor in accordance with the enlarging magnification by the aforesaid finder magnification means and the measured value by the aforesaid metering means. Furthermore, for an electronic camera according to the present invention, the foregoing observation area modifying means includes the observation area displaying means which displays the observation area in the object image observable through the foregoing optical finder, and the display modifying means which modifies the display area of the foregoing observation area displaying means. The aforesaid reading area modifying means is capable of changing the size of the area from which to read out the signals of the foregoing image sensor in accordance with the display area of the foregoing display modifying means. An electronic camera according to the present invention further includes a taking lens to image the aforesaid object image on the aforesaid image sensor, and metering means for measuring the distance between the object and the electronic camera, and the foregoing reading area modifying means is capable of changing the size and positions of the area from which to read out the signals of the aforesaid image sensor in accordance with the display area by the foregoing finder display modifying means and the measured value by the foregoing metering means. In a certain aspect of the present invention, an object can be enlarged electronically by the aforesaid reading area modifying means which may read a part of the light receiving area of the image sensor so as to make it to be a photographing magnification corresponding to the enlarging magnification of the optical finder. As a result, there is no need for any provision of a mechanism to interlock two optical members, the zoom lens and zoom finder; making it possible to implement the miniaturization of the camera. In another aspect of the present invention, it is possible to prevent any generation of parallax by the reading area modifying means which may change not only the size of the reading area for the image sensor, but also the position thereof in accordance with the enlarging magnification of the finder and the measured value by the metering means as well. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a view schematically showing the structure of an embodiment according to the present invention. Fig. 2A is a view illustrating an image observable in a zoom finder. Fig. 2B is a view illustrating an image projected on an image sensor. Fig. 3A is a view illustrating an image observable in a zoom finder. Fig. 3B is a view illustrating an image projected on an image sensor. Fig. 4 is a view illustrating a method for calculating a correction amount of a reading area for an image sensor according to an embodiment of the present invention. Fig. 5 is a view schematically showing the structure of another embodiment according to the present invention. Fig. 6 is a view schematically showing the structure of an electronic camera according to the prior art. Fig. 7 is a view schematically showing the structure of an electronic camera according to the prior art. Fig. 8A is a view illustrating an image observable in the zoom finder of a conventional electronic camera. Fig. 8B is a view illustrating an image projected on an image sensor. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the description will be made of the present invention specifically in accordance with the embodiments thereof, but it is to be understood that the present invention is not limited to such embodiments. Fig. 1 to Fig. 4 are views illustrating a first embodiment according to the present invention. Fig. 1 is a view schematically showing the structure of an electronic camera according to the present embodiment, but the same reference marks are given to the same members as or corresponding members to those appearing in Fig. 6 and Fig. 7 where conventional electronic cameras are shown. Therefore, the description will be made chiefly of its difference from the conventional electronic cameras. An electronic camera 1 according to the present embodiment is provided with an optical finder (zoom finder) 3 capable of varying its enlarging magnification. With the exception of this finder, it is provided as in the electronic camera shown in Fig. 7 with an image sensor 4, a zoom lens 2 which images the object image on the foregoing image sensor 4, a zooming lever 8 whereby to change the photographing magnification, a metering device 7 to measure the distance to an object, an image memory 9 to store the image formed on the image sensor 4, a recording medium 6 to record the object image to be photographed, and a control device 5. To describe the photographing operation by this electronic camera, a photographer 11 observes an object 10 though the zoom finder 3 to operate the zooming lever 8 to obtain a desired photographing magnification. When this zooming lever 8 is held down to the left in Fig. 1, a switch SW1 is turned on. Then, a member 3a of the zoom finder 3 is driven by a driving device which is not shown and is shifted to enlarge the object image in a given field frame; thus causing the enlarging magnification to be increased. On the other hand, when the zooming lever 8 is held down to the right in Fig. 1, a switch SW2 is turned on. Then, the member 3a of the zoom finder 3 is driven by a driving device which is not shown and shifted in the direction opposite to the foregoing operation to reduce the enlarging magnification of the zoom finder 3. Subsequently, when the photographer 11 having obtained a desired object image in the finder 3 depresses a release button which is not shown, the distance to the object 10 is measured by the metering device 7. A member 2B of the optical system of the zoom lens 2 is driven by a driving device which is not shown on the basis of the foregoing measured value of the distance to cause the object image to be focused on the image sensor 4. Thus, the image projected on the foregoing image sensor 4 is photoelectrically converted by the control device 5 to be inputted into the image memory 9 and recorded on the recording medium 6. Here, the object image observed by the photographer 11 in the finder 3 of this electronic camera 1, and the object image formed on the image sensor 4 for recording are shown in Fig. 2A and Fig. 2B thereby to describe the photographing principle of this electronic camera 1. Fig. 2A is a view illustrating the image observable in the zoom finder 3. Fig. 2B is a view illustrating the image projected on the image sensor 4. In this electronic camera, a part of the area C in the image B projected on the image sensor 4 is read in accordance with the enlarging magnification of the object image A observable in the zoom finder 3, and is recorded on the recording medium 6 in the form of an enlargement. Such a reading area C as this becomes smaller as the enlarging magnification of the zoom finder 3 becomes greater. Therefore, the object in the area C is further enlarged and recorded in the recording medium 6. Now, if the photographing distance of the object (distance between the object and the camera) is comparatively long and an angle  formed by the optical axis P1 of the zoom finder 3 and the central optical axis P2 passing the zoom lens (taking lens) 2 is small, the object observable in the zoom finder 3 is imaged substantially in the center of the image sensor 4. However, if the photographing distance of an object is short and the aforesaid angle  is large, the image which should be observable in the center of the zoom finder 3 is imaged in the direction opposite to the finder 3 (downward in Fig. 1) from the center of the image sensor 4. Thus, in the conventional electronic camera, the problem of parallax is encountered as described earlier. In this electronic camera 1, however, such problem is solved as described below. In other words, as shown in Fig. 3B, an area C' which is displaced downward in Fig. 3B from the center of the image sensor is read, instead of the foregoing reading area C, and is enlarged and recorded in the recording medium. In this way, the same image as observed in the finder can be recorded on the recording medium. Such a correction amount as this for the reading area is calculated as given below. Now, with reference to Fig. 4, W is a distance between the optical axis P1 of the zoom finder 3 and the optical axis P2 of the taking lens 2, L is a distance between the taking lens 2 and an object 10, f' is a distance between the taking lens 2 and the image sensor 4, and x is a distance between the image formation position of the object and the center of the image sensor. Here, given the focal length of the taking lens 2 as f, the following expression is formulated by the image formation formula of the lens: 1/L + 1/f' = 1/f Also, the following expression is formulated by the relationship of the geometrical similarity: W/L = x/f' When these expressions (1) and (2) are solved for x, the following expression is obtained: x = W/(L/f - 1) Thus, the displacement between the center of the image sensor and the image formation position of the object, that is, the correction amount x for the reading area, can be obtained according to this expression. Therefore, if the foregoing reading area is displaced in the direction opposite to the finder by the distance x from the central point of the image sensor, it becomes possible to record the same image as observed in the finder on the recording medium. Thus, the aforesaid parallax problem can be solved. In this respect, if the photographer desires an image taking in a wide range and the zooming magnification is small, the reading area C becomes large to make the difference (at y in Fig. 2) between the reading area C and the light receiving area B of the image sensor zero or smaller than the x. In this case, it becomes impossible to displace the reading area by the distance x obtained by the foregoing expression (3). However, when an image is photographed in a wide range such as this, the ratio of the area occupied by the object image in the reading area C is so small that any parallax cannot be conspicuous. Therefore, there is no essential problem. Furthermore, in an electronic camera according to the present embodiment, the finder 3 and the taking lens 2 are arranged in the positions above and below in the vertical direction. Consequently, the structure is arranged so that the foregoing correction of the reading area C is made in the vertical direction. However, it may be possible to arrange the finder 3 and the taking lens 2 in the horizontal direction. In such a case, the correction of the reading area C will be performed in the horizontal direction. Also, in the present embodiment, while a zoom finder capable of varying the enlarging magnification continuously is used, it may be possible to employ, in place of the foregoing finder, a finder of a plural-focus point type wherein several kinds of enlarging magnifications can be selected by switching over parts of finder optical system. Further, in the present embodiment, a taking lens of a fixed focal length type is used, but it may be possible to construct a camera having a large zooming ratio by the use of a taking lens capable of varying its focal length thereby to enable the size of the reading area of an image to be varied electrically. Here, another embodiment is shown in Fig. 5, but this embodiment is such that instead of the zoom finder 3 provided for the foregoing first embodiment, an optical finder 23 of a fixed magnification is employed, and that in the aforesaid finder 23, displaying means 23a is provided to display the photographing area by a variable frame in the finder. Then, in this electronic camera 21, an image is read from a part of the area of the image sensor 4 in accordance with the enlarging magnification displayed by the variable frame in the foregoing optical finder 23, and the aforesaid image is recorded on the recording medium 6. Thus, since an optical finder of a fixed magnification type is used according to the present embodiment, it is possible to implement the further reduction of the manufacturing cost than the foregoing first embodiment. As described above, according to the present invention, there is no need for any mechanically interlocked mechanism for a finder and a taking lens. Thus, it is possible to implement the miniaturization of a camera, and the reduction of manufacturing cost, and to prevent the generation of parallax.

Claims: An electronic camera having an image sensor (4) to receive the rays from an object (10) and convert them into electrical signals, comprising: an optical finder (3,23) for the observation of an object image having observation area modifying means (3a, 23a) to modify the observation area of the object to be photographed; reading means to read the signals from a part of the area (C) of an image (B) the rays of which are received by said image sensor; recording means (6) to record the signals read by said reading means, characterized by reading area modifying means to modify the size of said area of the image thereby to read the signals from said image sensor in accordance with the observation area modified by said observation area modifying means. An electronic camera according to claim 1, wherein said observation area modifying means comprises finder magnification modifying means (3a) to modify the observation area by changing the enlarging magnification of said optical finder (3), and said reading area modifying means modifies the size of the area (C) read from said image sensor (4) in accordance with the enlarging magnification by said finder magnification modifying means. An electronic camera according to claim 1, wherein said observation area modifying means includes observation area displaying means (23a) to display the observation area in an object image through said optical finder (23) by a variable frame in said finder, and said reading area modifying means modifies the size of the area (C) thereby to read the signals from said image sensor in accordance with the enlarging magnification displayed by the variable frame. An electronic camera according to claim 2 or 3, wherein said reading area modifying means is adapted to also modify the position of the area (C) of the image to thereby correct for any parallax between the object observed by the optical finder (3, 23) and received by the image sensor (4).

Inventors: EJIMA SATOSHI, EJIMA, SATOSHI
Applicants: NIPPON KOGAKU KK, NIKON CORPORATION
Application year: 1993
Main classification: H04N5
IPC codes: H04N5, H04N3, G03B13, G02B7