Digital Camera Patent Abstract
A digital camera which uses the resources of silver halide single
lens reflex cameras to provide an angle of field equal to that of
a silver halide single lens reflex camera without enlarging the
size of the image sensing element, and which provides excellent
holding characteristics because the camera body is not elongated
in the backward direction. A taking lens for a silver halide single
lens reflex camera is used as a taking lens 301. A digital camera
provided with a reducing lens 302 disposed behind a taking lens
in the direction of the optical axis of the taking lens and on the
optical axis of the taking lens, and a CCD sensor 303 for photoelectrically
converting an optical image transmitted through the taking lens
and the reducing lens, and which is disposed at the composite focus
point of the taking lens and the reducing lens. This construction
ensures the field angle is identical to that of a silver halide
single lens reflex camera even when a small size image sensing element
is used. The camera body is also compact. Digital Camera Patent Claims
What is claimed is:
1. A digital camera which uses a taking lens for a camera for use
with a silver halide film, comprising: an optical system removably
disposed between an install position of the taking lens and a focal
plane of the taking lens; and an image sensing element disposed
at a composite focus plane of the taking lens and the optical system.
2. A digital camera according to claim 1, wherein said optical
system includes a reduction optical system.
3. A digital camera according to claim 1, wherein a focal length
of the optical system and a distance between the taking lens and
the optical system are set so that a relationship between the composite
focal length and a field angle of the image sensing element equals
a relationship between the focal length of the taking lens and a
field angle of the silver halide film.
4. A digital camera comprising: a mount on which a removable reduction
optical system can be is installed; and an image sensing element
disposed at a composite focus plane of the reduction optical system
and a taking lens which is positioned in front of the reduction
optical system.
5. A digital camera according to claim 4, wherein the taking lens
is an exchangeable taking lens for a camera using silver halide
film.
6. A digital camera according to claim 5, wherein a focal length
of the optical system and a distance between the taking lens and
the optical system are set so that a relationship between the composite
focal length and a field angle of the image sensing element equals
a relationship between the focal length of the taking lens and a
field angle of the silver halide film.
7. An image sensing method for a digital camera, comprising the
following steps: reducing, by a removable reduction optical system,
an image transmitted through an exchangeable taking lens; forming
a reduced image on an image sensing element; and generating image
data based on an output of the image sensing element.
8. A digital camera according to claim 1, wherein the taking lens
is installable to the digital camera with a close-up ring in place
of the optical system.
9. A digital camera according to claim 1, wherein a warning is
provided when the taking lens is inappropriate for the optical system.
10. A digital camera according to claim 5, wherein the taking lens
is attachable to the digital camera with a close-up ring in place
of the removable reduction optical system.
11. A digital camera according to claim 5, wherein a warning is
provided when the taking lens is inappropriate for the reduction
optical system.
Digital Camera Patent Description
This application is based on application No. 10-180946 filed in
Japan, the content of which is hereby incorporated by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a digital camera using a taking
lens used by cameras using media of different sizes and image sensing
elements such as a CCD and the like, and specifically relates to
a digital camera using a taking lens for cameras using silver halide
film.
2. Description of the Related Art
In recent years, digital cameras have become popular replacements
for cameras which use silver halide film in conjunction with advances
in semiconductor and image processing arts. Such digital cameras
basically take an optical image from a taking lens and subject the
image to photoelectric conversion via image sensing element such
as a charge-coupled device (CCD) or the like, subject the converted
output data to image processing, and store the image data on a storage
medium such as a memory card or the like.
A digital camera which makes practical use of the assets of the
silver halide single lens reflex camera has been proposed during
the popularization of the digital camera. This camera provides the
body of a silver halide camera comprising a magazine at one end
in the film length direction, compartment for the power source batteries
E1-E4 at the opposite end, and a grip G, used directly as a camera
body 2, as shown in FIGS. 8 and 9.
This camera is provided with a shutter button 9 on the top surface
of the grip G of the camera body 2 provided with a viewfinder 3;
a taking lens 301 for a single lens reflex camera is installed on
the front mount 25, a quick return mirror M1 and focal plane shutter
26 and the like are provided behind the taking lens 301 in the optical
axis direction, and a CCD 303 is disposed at a position on the optical
axis near the film gate 29.
When the shutter button 9 is pressed, the quick return mirror M1
is rotated to the dashed line position in FIG. 9 so as to be retracted
from the photographic optical path, and directly thereafter the
focal plane shutter 26 is opened, the object image viewed through
the finder 3 forms an image on the CCD 303, and the CCD 303 converts
this image to an optical image via photoelectric conversion. The
focus point of the taking lens 301 is automatically focused by an
auto focus (AF) actuator 220 provided at a suitable location within
the camera body 2.
As mentioned above, when a CCD receives light using a taking lens
301 of the silver halide single lens reflex camera, the size of
the CCD and the size of the silver halide film must be equal, as
shown in FIG. 8, to ensure the same field angle as the silver halide
single lens reflex camera. A large CCD 303 equivalent to the aforesaid
film is difficult to manufacture and produces an extremely poor
yield in the current state of the art. Conversely, when a conventional
small CCD 303, such as a 1/2 inch size, is used, the field angle
is reduced because light only reaches the center area of the film
frame, and an adequately wide angle photograph cannot be obtained.
To eliminate this disadvantage, it has been proposed to remove
the back cover of the silver halide single lens reflex camera, and
arrange the CCD 303 through a relay lens behind the focus point
of the taking lens 301. According to this construction, an image
formed at a certain position on conventional film is relayed via
the relay lens, and reduced to a size matching the size of the CCD
so as to form an image on the CCD.
In this construction, however, the camera body is elongated in
the back, so as to make it extremely difficult to hold the camera,
and increasing the susceptibility to so-called camera vibration
and the like.
SUMMARY OF THE INVENTION
In view of the aforesaid information, an object of the present
invention is to provide a digital camera that does not increase
the size of the camera body even when constructed using a small
type image sensing element.
These objects are attained by the digital camera of the present
invention which uses the taking lens for a silver halide camera,
comprises an optical system disposed between an install position
of the taking lens and a focal plane of the taking lens; and an
image sensing element disposed at a composite focus plane of the
taking lens and the optical system.
Another digital camera of the present invention comprises: a mount
on which exchangeable taking lens is installed; an optical system
disposed between the mount and a focal plane of the taking lens;
and an image sensing element disposed at a composite focus plane
of the taking lens and the optical system.
BRIEF DESCRIPTION OF THE DRAWINGS
These and other objects and features of this invention will become
clear from the following description, taken in conjunction with
the preferred embodiments with reference to the accompanied drawings
in which:
FIG. 1 is a is a top plan sectional view of a digital camera of
an embodiment of the present invention;
FIG. 2 is a side sectional view of the digital camera;
FIG. 3 is a rear view of the digital camera;
FIG. 4 is a block diagram of the control system of the digital
camera of FIGS. 1-3;
FIG. 5 is a front view of a digital camera of another embodiment
of the present invention shown with the reducing lens removed;
FIG. 6 is a perspective view of the reducing lens of the digital
camera of FIG. 5;
FIG. 7 is a front view of the digital camera of FIG. 5 shown with
the reducing lens installed;
FIG. 8 is a top plan sectional view of a conventional digital camera
with a silver halide single lens reflex camera taking lens installed;
and
FIG. 9 is a side sectional view of thew conventional digital camera
of FIG. 8.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
A digital camera 1 has an oblong box-like camera body 2, and a
taking lens 301, which is a replaceable lens for a silver halide
single lens reflex camera, is mounted on a lens mount, as shown
in FIGS. 1-3.
The taking lens for the silver halide single lens reflex camera
normally has a flange back set at approximately 40 mm, such that
the incident light rays L focus on the focus point F0 position in
FIG. 1.
Within the camera body 2, a reducing lens 302 is provided as a
reduction optical unit arranged behind the taking lens 301 in the
optical axis direction on the same optical axis as the taking lens
301. The composite focus point of both the taking lens 301 and the
reducing lens 302 is at position F1 on the taking lens side from
the position F0, and a image sensing element CCD sensor 303 is disposed
at this position F1. Accordingly, the thickness of the camera body
2 in the direction of the optical axis is thinner than that of a
silver halide single lens reflex camera, and the camera body 2 is
formed as a thin body in the present embodiment. An actuator 220
for driving the taking lens 301 is arranged in the bottom part of
the camera body 2.
The image frame size of the CCD 303 is 18.times.12 mm horizontal-by-vertical,
and the number of pixels is 1800.times.1200=2,160,000 pixels. When
a standard lens having a focal length of 50 mm is used as the taking
lens 301 and the composite focal length fc of the taking lens 301
and the reducing lens 302 is not 25 mm, a field angle equivalent
to the field angle of a silver halide single lens reflex camera
cannot be obtained. If the focal length of the taking lens 301 is
designated f1, the distance between the taking lens 301 and the
reducing lens 302 is designated e, and the focal length of the reducing
lens is designated f2, the Equation (1) below obtains.
In this example, the distance e between the lenses 301 and 302
is 30 mm, and the focal length f2 of the reducing lens is set at
20 mm.
In this way, for example, the field angle when photographing using
a taking lens 301 with a focal length of 50 mm mounted on the camera
body of a silver halide single lens reflex camera matches the field
angle when photographing using the taking lens installed on the
camera body 2 of the present embodiment. Accordingly, a user may
use the camera without the requirement of considering conversion
of the focal length of the taking lens.
In general, the following equation (2) must be satisfied to match
the field angle when using a taking lens installed on the camera
body of a silver halide single lens reflex camera with the field
angle when the lens is installed on the camera body 2 provided with
a reducing lens as in the present embodiment using a CCD sensor
303 which is 1/n the size of 1 frame of the silver halide film.
When using a reducing lens 302 and a CCD sensor 303 of the size
in the present embodiment, and when the taking lens 301 is a telephoto
lens having a focal length f1=135 mm, the values n=2, f2=20 mm,
and e=115 mm.
There are also instances where the value e cannot be set to a value
determined by equation (2) depending on the type of taking lens
301. In such instances, the position of the reducing lens 302 is
moved forward or back to set the value e at a value determined by
equation (2).
In order to determine the type of taking lens 301 installed in
the camera body 2 of the digital camera shown in FIGS. 1-3, a contact
200 is provided within the camera body 2 for reading information
in a ROM 201 installed in the taking lens 301, such that the type
of installed taking lens 301 is determined via this ROM 201, and
the actuator 221 for moving the reducing lens is driven in accordance
with this information so as to move the reducing lens 302 in a forward
or backward direction.
A liquid crystal display (LCD) 10 is provided on the back side
of the camera body 2. The LCD 10 is used as a viewfinder to monitor
photography and to display a regeneration of the recorded image.
On the bottom part of the left rear surface of the camera body
2 are provided a compression ratio setting slide switch 12 for switching
the compression ratio K of the image data recorded on a memory card
8, and a photography/regeneration mode setting switch 14 for switching
between the photography mode and the regeneration mode. The digital
camera 1 allows selection of two compression ratios K, i.e., 1/8
and 1/20; for example, the compression ratio K is set at 1/8 when
the compression ratio setting switch 12 is moved to the right side,
and the compression ratio K is set at 1/20 when the switch 12 is
moved to the left side. Of course, increasing or decreasing the
types of compression ratios K is optional.
The photography mode is a mode for photographing, i.e., recording,
and the regeneration mode is a mode for regenerating and displaying
the photographed image stored on the memory card 8 on the LCD display
10. The photography/regeneration mode setting switch 14 is also
a two-contact sliding switch; for example, the regeneration mode
is set when the switch 14 is moved to the right, and the photography
mode is set when the switch 14 is moved to the left.
Four-linked press button switches SW are provided above the LCD
display 10. The lateral two button 6 and 7 allocate the frame advance
functions to regenerate a recorded image. The switch 6 advances
the frame of the recorded images in the direction of increasing
frame number (photographic order direction) (hereinafter referred
to as the "UP key"), and the other switch 7 advances the
frame of the recorded images in the direction of decreasing frame
number (hereinafter referred to as the "DOWN key").
A power switch PS comprising a rotary switch is provided on the
top surface of the camera body 2, and a shutter button 9 is provided
on the top of the grip G. An autofocus (AF) actuator 220 for driving
the taking lens 301, and an actuator 221 for driving the reducing
lens 302 are respectively provided on the bottom surface of the
camera body 2.
The interior of the grip G forms a battery compartment, which accommodates,
for example, AA-size dry cell batteries E1-E4 as a power source
to drive the various components.
On one side of the camera body 2 is formed a slot 5 into which
can be removably inserted a memory card 8 as an example of a recording
medium for recording photographed images. In the vicinity of the
slot 5 is provided a connector 214 for electrically connecting the
digital camera 1 to an external personal computer 19 (refer to FIG.
4).
FIG. 4 is a block diagram of the control system of the digital
camera 1.
The CCD 303 is a color area sensor, which photoelectrically converts
an optical image of an object formed by the taking lens 301 and
the reducing lens 302 into signals comprising a signal array of
image signals received by each pixel, and outputs these signals
as image signals of the color components red (R), blue (B), and
green (G) via color filters arranged in a specific pattern. A timing
generator 314 generates various timing pulses for controlling the
actuation of the CCD 303. The timing generator 314 generates signals
for controlling the operation of the CCD 303 based on standard clock
signals transmitted from a dining control circuit 202. For example,
the dining generator 314 generates integration start/end (exposure
start/end) timing signals, and clock signals for the read control
signals (horizontal synchronization signal, vertical synchronization
signal, transmission signal and the like) for reading the photoreception
signals of each pixel, and outputs these signals to the CCD 303.
A signal processing circuit 313 performs predetermined analog signal
processing of image signals (analog signals) output from the CCD
303. The signal processing circuit 313 has a correlation double
sampling (CDS) circuit, and an auto gain control (AGC) circuit,
so as to reduce the noise of the image signals via the CDS circuit,
and adjust the level of the image signals by adjusting the gain
of the ACG circuit.
An analog-to-digital (A/D) converter 205 converts each pixel signal
of the image signal to a 10-bit digital signal. The A/D converter
205 converts each pixel signal (analog signal) to a 10-bit digital
signal based on the A/D conversion clock signal input from the timing
control circuit 202.
A black level correction circuit 206 corrects the lowest level
included in the A/D converted pixel signals (hereinafter referred
to as "pixel data") to a standard black level. A white
balance circuit (hereinafter referred to as "WB circuit")
207 converts the level of the pixel data of each R, G, B color component
so as to adjust the white balance after gamma correction. The WB
circuit 207 converts the level of the pixel data of each R, G, B
color component using a level conversion table stored in the general
controller 211. The conversion coefficient (characteristics slope)
of each color component of the level conversion table is set for
each photographic image by the general controller 211.
The gamma correction circuit 208 corrects the gamma characteristics
of the pixel data. The gamma correction circuit 208 has, for example,
six types of gamma correction tables of different gamma characteristics,
and performs gamma correction on pixel data via a specific gamma
correction table in accordance with the photographic scene and photographic
conditions.
An image memory 209 stores the pixel data output from the gamma
correction circuit 208. The image memory 209 has a storage capacity
of one frame. That is, the image memory 209 has a pixel data storage
capacity equal to that of the CCD 303, i.e., 1200.times.1800=2,160,000
pixels, and stores the pixel data at a corresponding pixel position.
A VRAM 210 is a buffer memory for image data regenerated for display
on the LCD display 10. The VRAM 210 has a pixel data storage capacity
corresponding to the number of pixels of the LCD display 10.
In the photographic standby state, the pixel data of an image sensed
30 times per second by the CCD 303 are subjected to predetermined
signal processing by each circuit from the A/D converter 205 to
the gamma correction circuit 208, and thereafter the image data
are stored in the image memory 209, and subjected to reduction processing
in accordance with the number of pixels of the LCD display 10 via
the general controller 211, then transmitted to the VRAM 210 for
display on the LCD display 10. In this way, the photographer is
able to view the object image via the image displayed on the LCD
display 10. In the regeneration mode, an image read from the memory
card 8 is subjected to predetermined signal processing by the general
controller 211, and thereafter transmitted to the VRAM 210 for regeneration
and display on the LCD display 10.
At this time, the general controller 211 discriminates the contrast
of the center area of the image data stored in the image memory
209, and controls the AF actuator 220 to maximize the contrast,
and maintain the focused state.
Reference number 204 refers to a diaphragm control driver, which
controls the values that set the diaphragm value of the taking lens
301 via instruction from the general controller 211.
The general controller 211 discriminates the type of taking lens
301 by referencing information recorded in ROM within the taking
lens 301 via the contact 200. In this way, the reducing lens 302
is moved to a predetermined position via a moving mechanism not
shown in the drawing by referring to a corresponding table within
the general controller 211 to chive the reducing lens actuator 221.
This operation is performed again when the taking lens 301 is exchanged.
The aforesaid table is a table of correspondence between the type
of taking lens 301 and the aforesaid value e.
The card I/F 212 is an interface for writing image data to and
reading image data from the memory card 8. The communications I/F
213 is a standard USB interface for connecting to a personal computer
19 to enable communications.
The RTC 219 is a clock circuit for managing the photograph date,
and is driven by a separate power source not shown in the drawing.
The operation panel 250 is an input/output device for the general
controller 211, and comprises the UP key 6, the DOWN key 7, the
shutter button 9, the power switch PS, the compression setting switch
12, and the photography/regeneration mode setting switch 14.
The general controller 211 is a microcomputer, which organically
controls the actuation of various components within the camera body
2 and the image sensing unit 3, and performs the general controls
of the photographic operations of the digital camera 1.
The general controller 211 is provided with a filter unit for filtering
processes, a recording image generator for generating thumbnail
images and compressed images for accomplishing photographic image
recording processing, and a regenerated image generator for generating
a regenerated image of an image recorded in the memory card 8 for
display on the LCD display 10.
The filter unit corrects image quality related to contours by correcting
the high frequency components to be recorded via a digital filter.
The filter unit is provided with a total of five digital filters
including a digital filter for standard contour correction, two
types of digital filters for strengthening contours relative to
the standard contour correction, and two types of digital filters
for weakening contours relative to the standard contour correction,
these filters operating at compression ratios K of 1/8 and 12/20.
The recording image generator reads the image data from the image
memory 209, and generates a thumbnail image and compression image
to be recorded on the memory card 8. The recording image generator
reads the pixel data at constant intervals in both the horizontal
direction and the vertical direction while scanning the image memory
209 in the raster scan direction, and generates thumbnail images
and records these images on the memory card 8 by sequentially transmitting
the image data to the memory card 8.
The recording image generator reads all image data from the image
memory 209, generates compressed image data by two-dimensional DCT
conversion of pixel data, which are then subjected to predetermined
compression processing by a JPEG method such as Huffman coding or
the like, and records the compressed image data in the present image
area of the memory card 8.
In the photographic mode, when the shutter button 9 is operated
to specify a photograph, the general controller 211 thereafter generates
a thumbnail image retrieved from the image memory 209, and generates
a compressed image compressed by a JPEG method via the compression
ratio K set by the compression setting switch 12, and both images
are recorded on the memory card 8 together with tag information
(frame number, exposure value, shutter speed, compression ratio
K, date, scene information, and image discrimination results) relating
to the photographic image.
When the memory card 8 has a capacity of 64 MB, it is capable of
storing the images of approximately 200 frames at a compression
ratio of 1/20; the tag data, high resolution image data compressed
by a JPEG method (1800.times.1200 pixels), and thumbnail display
image data (90.times.60 pixels) are recorded for each frame. For
example, the aforesaid information is managed as EXIF type image
files in frame units.
The digital camera 1 of this construction makes practical use of
available resources because it is capable of using the taking lens
301 of a silver halide single lens reflex camera. In particular,
the focal length is reduced because a reducing lens 302 is arranged
behind the taking lens 301 a short distance from the flange back,
and the CCD 303 is arranged at the composite focus point of the
reducing lens 302 and the taking lens 301, and the use of a small
size CCD 303 ensures the same field angle as a silver halide camera,
and does not hinder wide angle photography. The disposition of the
CCD 303 not only does not require elongation of the rear side of
the camera body 2, it actually makes the body thinner and more compact,
and improves the holding characteristics of the camera.
FIG. 5 shows another embodiment of the present invention; parts
common to FIGS. 1-3 at equivalent locations are omitted from this
description.
In FIG. 5, the reducing lens 302 is replaceable in accordance with
the taking lens 301 rather than moving the reducing lens 302 in
accordance with the taking lens 301.
Specifically, three bayonet members 331 are arranged in a circumferential
direction on the barrel 340 of the reducing lens 302, as shown in
FIG. 6, so as to render the reducing lens 302 detachably installable
on the camera body 2 by the removable engagement of the bayonet
members 331 with the mount 330 for the reducing lens 302 provided
on the interior side of the mount 20 of the taking lens 301. FIG.
7 shows the reducing lens 302 installed on the camera body 2.
In this way, an object image is suitably formed on the CCD 303
in accordance with the individual taking lens 301. When the reducing
lens 302 is removed, the taking lens 301 can be installed on the
camera body 2 via a well known close-up ring so as to be usable
for photography without the reducing lens 302. In this instance,
when the reducing lens 302 is removed and the taking lens 301 is
installed, an image is not formed on the CCD because the focus point
is F0. For this reason, installing the taking lens via the close-up
ring allows the entire taking lens to feed out in a forward direction,
so as to form the focus point on the CCD.
The use of a taking lens for a silver halide single lens reflex
camera and a digital camera reducing lens 302 allows photographs
to be taken at the same field angle as the taking lens of the silver
halide single lens reflex camera. It is also possible to take photographs
with the taking lens installed via a close-up ring without installing
the reducing lens 302, in which case the CCD sensor senses a trimmed
image because only the center area of the image is received, so
as to simulate the use of a long focus lens. Accordingly, this arrangement
advantageously allows a single replaceable lens to be used two ways.
This construction can also provide a warning when a taking lens
301 is installed which is inappropriate relative to the installed
reducing lens 302. In this instance, the type of reducing lens 302
can be discriminated by means of a marking or the like provided
on the reducing lens 302.
Although each of the embodiments has been described in terms of
the use of a single reducing lens 302, it is to be understood that
a plurality of such reducing lenses 302 may be used.
Obviously, many modifications and variation of the present invention
are possible in light of the above teachings. It is therefore to
be understood that within the scope of the appended claims, the
invention may be practiced other than as specifically described.
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