Still camera system

A still camera system comprises a camera body which carrys alternatively a film back or a still video back having a solid-state image pickup device for receiving still images in order to record them on a recording medium. The improved system includes a display, a first means for providing the display information on the film back installing mode, and a second means for providing the display information on the still video back installing mode.

BACKGROUND OF THE INVENTION AND RELATED ART STATEMENT 
The present invention relates to a still camera system which is able to 
selectably load with a film back and a still video back. 
There has been disclosed an electronic still camera which takes a still 
image using a solid-stage image pickup device such as a charge-coupled 
device (hereinafter referred to as CCD) and then records the still image 
on a magnetic disk. For example, at pages 80 to 85 of NIKKEI ELECTRONICS 
issued on July 2, 1984, a Japanese magazine has been introduced such a 
camera. Minolta Camera Kabushiki Kaisha, the assignee of this invention, 
has filed a Japanese Utility Model application of No. 36821/1986 relating 
to a still camera including a camera body to carry alternatively a still 
video back or a film back. This type of a still camera is constructed in 
such a manner that a still video back including a solid-state device and 
an image processing circuit is detachably mounted to a common camera body 
for carrying a film back. The camera is also constructed in such a manner 
that, even when loaded with the still video back, the camera remains 
compact in size and thus, the appearance of the camera is approximately 
similar to that of a popular single-lens reflex camera. Additionally, when 
loaded with the film back in place of the still video back, the camera can 
provide an image formed in the film plane in the same manner as a common 
single-lens reflex camera. 
While a common film camera of a film back type has a display for indicating 
exposure control modes, a shutter speed, diaphragm aperture value, and a 
film count number of exposed frames of a film, however, if the still video 
back is attached thereto, readings including a frame/field recording mode 
and a track number in place of the film count number should be displayed 
in addition to the aforesaid readings. It is generally known that such 
specific information relating to the still video back is displayed on the 
still video back. 
In such an arrangement, both of the displays on the camera body and the 
still video back should be observed at a time while the still video back 
is installed, which will cause a problem that a camera operator is 
required to read the information respectively. 
Additionally, the CCD image sensor contained within the still video back is 
generally 2/3-inch (8.6 mm.times.6.6 mm) or 1/2-inch (6.4 mm.times.4.9 mm) 
in measurements and smaller as compared to the size of a frame of a 35 mm 
film (36 mm.times.24 mm). For example, as shown in FIG. 13, when the CCD 
is 2/3-inch in size, its picture screen 35 on the film plane is 17.6 mm 
wide by 13.2 mm high at a reducing rate of 1/2 on a relay optical device 
contained within the still video back. It is possible to provide a picture 
image exactly on the CCD with the use of a relay optical device which can 
reduce the size of a 35 mm film screen to that of the CCD, which will be 
equivalent to filming on the 35 mm frame. However, in this case, such a 
relay optical device in the still video back becomes greater in size thus 
to decline the portability when the still video back is attached to the 
camera body. 
Therefore, a system has to be developed to meet the respective screen sizes 
of the film back and the still video back whichever is installed. In that 
case, there will be some elements, e.g. an area of measuring light and an 
area of focus detection, to be varied according to the size of a picture 
screen. Two resepctive areas of measuring light are shown in FIG. 14-A 
wherein an area 36 is for a 35 mm film while an area 37 is for the still 
video back. Similarly, two focus detecting areas are shown in FIG. 14-B 
wherein an area 38 is for a 35 mm film while an area 39 is for the still 
video back. Apparently, the light-measuring area and focus detecting area 
37, 39 with the still video back installed becomes small in accordance 
with the size of the CCD. It will be a better idea that a frame display 
representing the frame of the focus detecting area in the viewfinder is 
changed in relation to the focus detecting area. 
Furthermre, there will be some other elements to be changed and/or modified 
without relation to the size of a picture screen. For example, the 
information on film sensitivity required for exposure calculation has to 
be adjusted to that on equivalent film sensitivity determined by the 
sensitivity of CCD image sensor, and the restriction of shutter speed and 
diaphragm aperture value has to be ranged according to the attachment of 
the film back or the still video back. For a 35 mm film camera, diaphragm 
aperture ranges from the smallest opening to the greatest opening in an 
interchangeable lens to be used. When the still video back is installed, 
the available full opening aperture is limited in size by a diameter of a 
lens in a relay optical device provided in the still video back. That is, 
in case that the lens diameter of the relay optical device is smaller than 
the equivalent to the full-open diaphragm aperture value of the 
interchangeable lens, the result of calculation will be incorrect when 
measuring under the full-open diaphragm aperture. Consequently, when the 
still video back is installed, the available diaphragm aperture ranges 
from the smallest opening aperture to the interchangeable lens to 
whichever of the largest opening aperture in the interchangeable lens and 
the lens in the relay optical device is smaller. 
When the shutter is slow, an S/N ratio according to a dark current in the 
CCD becomes smaller thus to reduce the quality of a picture image to be 
recorded, which is a specific set-back in CCD. Therefore, the shutter 
control has to be restricted on the slow side so as not to exceed a 
certain shutter speed such as 1/2 second or 2 second. 
Furthermore, after a back cover of the camera body is opened, so-called 
initial film loading is carried out by advancing the film automatically 
until a not-exposed frame of the film is advanced to a photographic 
position. When the still video back is installed in place of a back cover, 
the initial loading is not required since erasing and recording on the 
magnetic disk can be effected automatically and electrically. 
SUMMARY OF THE INVENTION 
It is a first object of the present invention to provide a still camera 
system which displays with the still video back attached thereto in such a 
manner that the readings of photographing information are appropriate to 
the still video back installing mode and thus, facilitates checking of the 
readings in the still video back installing mode. 
It is a second object of the invention to automatically provide an optimum 
condition for photographing while either the film back or the still video 
back is installed. 
A still camera system of the present invention has a camera body which is 
arranged to carry alternatively a film back or a still video back having a 
solid-state image pickup device for receiving still images in order to 
record them on a recording medium, a display, a signal input means for 
receiving input signals indicating the attachment of either the film back 
or the still video back, a first means for providing the display 
information in a film back installing mode to said display, a second means 
for providing the display information in a still video back installing 
mode to said display, and a switching means for selecting between said 
first and second means corresponding to the input information of said 
signal input means; whereby the readings in the film back installing mode 
and the still video back installing mode are alternatively displayed on 
the display of the camera body. 
Accordingly, one single display can visibly indicate all the information. 
Also, the display readings can be selected automatically. Furthermore, an 
optimum condition for photographing can be attained not only when the film 
back is installed but also when the still video back is installed.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
Referring to FIG. 1 showing a section of a still camera system of the 
present invention, a camera body 1 having the same construction as a usual 
single-lens reflex camera is loaded with a still video back 2 in place of 
a film back, and an electronic flash unit 3 mounted over a pentaprism 17. 
An interchangeable lens 4 is provided with an objective lens 5, a 
diaphragm aperture 6, a diaphragm aperture driving mechanism 7, and a ROM 
chip 8 holding information concerning the lens; such as a focal length and 
a full-open diaphragm aperture value. The camera body 1 carries a main 
mirror 9 for introducing an image to a viewfinder, a sub miror 10 for 
reflecting light passed through a half transparent portion of the main 
mirror 9 for the light measurement and the focus detection, a photocell 12 
for measuring the brightness of the subject in natural light or flashlight 
by receiving light reflected by the submirror 10 and passed through a lens 
11, a CCD line sensor 14 for measuring the focussing condition of the 
interchangeable lens 4 by receiving light reflected by the submirror 10 
and passed through a lens 13. The plane corresponding to the film plane is 
disposed near the rear surface of a focal plane shutter 15. A viewfinder 
portion in the camera body includes a focus plate 16, the pentaprism 17, 
and an eyepiece lens 18. The still video back 2 includes a relay optical 
portion 19 for reducing the image size of the 35 mm film frame to that of 
2/3-inch, a relay viewfinder portion 20 for shifting the eyepoint of 
viewfinder to the rear of the still video back 2, a signal processing 
circuit board 22 having a CCD image sensor 21, an image forming circuit 23 
having a recording circuit, a control circuit 24 having a still video back 
contol microcomputer, a mechanical device (not shown) having a motor for 
driving a head for recording an image on a magnetic disk. The flash unit 
3, which is mounted on a hot shoe 25 of the camera body 1, is equipped 
with a flash control circuit 27 for controlling activation of xenon lamp 
26, means 28 for setting flashlight emission angle to be driven based on 
focal length information of the interchangeable lens 4, and a lens 29 for 
light projection. The flashlight coverage setting means 28 includes a 
motor, a motor control circuit, transmission gears 30 and 31 for 
transmitting the rotation of the motor, a rack gear 32 meshed with the 
gear 31, and a cylinder 33 holding the lens 29 on the forward end thereof, 
whereby the lens 29 is moved forward and backward in accordance with the 
focal length information of the lens 4. 
FIG. 4 is a block diagram of the substantial arrangement of the camera body 
with the still video back installed according to the system of the present 
invention. As shown, in FIG. 4, the camera body 1 is shown in the left 
side of a partition line 40 and the still video back 2 is shown in the 
right side of the same. The numeral 41 is a camera control microcomputer 
which is installed within the camera to be the central control unit of the 
camera system and activated by command signals from switches S1, S2, S3 
and S4. The switch S1 is a light-measuring switch which is turned on when 
a release button 54 is pressed halfway and thus, light measurement, focus 
detection and data exchange, etc will commence. When the switch S1 remains 
on, each circuit of the system is live. The switch S2 is a release switch 
which is turned on when the release button S4 is pressed to a full extent 
and thus, exposure control operation of the camera will commence. The 
switch S3 is a rear cover detecting switch which will be turned on when 
the rear cover is closed (or the still video back is installed). 
Represented by SW is a pulse generating circuit which sends one pulse to 
an interrupt terminal INT2 when the switch S3 is turned from its 
on-position to its off-position and vice versa. The switch S4 is adopted 
for indicating the state of film advancing and shutter cocking and will be 
turned on when the exposure control operation on the camera is completed 
and off when the film advancing and shutter cocking are completed. 
The numeral 42 is a light measuring circuit which, as activated when the 
switch S1 is turned on, measures the brightness of an object to be 
photographed according to input signals from first and second 
photoelectric converting elements SPC1, SPC2 and, upon converting the 
resulting data into digital signals, sends the digital signals to the 
camera control microcomputer 41. The second photoelectric converting 
element SPC2 is used in either mode of the film back or of the still video 
back while the first photoelectric converting element PSC1 is particularly 
used only in the film back installing mode. Such selection can be made by 
means of a switch 43 which is switched according to control signals sent 
via the light measuring circuit 42 from the camera control microcomputer 
41. 
The first photoelectric converting element SPC1 is provided for receiving 
light in a relatively wide area of a camera viewfinder while the second 
photoelectric converting element SPC2 is provided for receiving light in a 
small area thereof about the center of the camera viewfinder, and is used, 
in the film back installing mode, for so-called spot light measurement. 
The numeral 44 is a microcomputer for auto-focus control which exchanges 
signals with the camera control microcomputer 41 and additionally, 
activates an auto-focus motor 46 for focusing in accordance with the 
resulting data upon detecting focus condition of the interchangeable lens 
4 in relation to the data from a photocell 45 for focus detection. The 
numeral 47 is a display device including liquid crystal display (LCD) 
which indicates various data. The camera control microcomputer 41 can also 
receive various data, e.g. film sensitivity SV with the film back 
installed and will in turn send control signals to a controlled circuit 48 
for film advancing, shutter travelling, diaphragm driving, etc. 
The still video back 2 comprises a video back control microcomputer 50, a 
video back circuit 51 including CCD image sensor, signal processing and 
recording circuits, and a mechanism block 52 for driving a magnetic disk 
and a head. The still video back 2 further comprises a switch S5 for 
choosing between the modes of field recording and frame recording to 
record the data on a magnetic disk and a CCD sensitivity output circuit 53 
which outputs a CCD sensitivity data equivalent to a film sensitivity. The 
switch S5 sould be turned on for the frame recording and off for the field 
recording. The camera control microcomputer 41 and the video back control 
microcomputer 50 exchange data via four signal lines l1, l2, l3 and l4. A 
start-up signal of exchanging the data is sent from the camera control 
microcomputer 41 through the line l1 in response to the turn-on of the 
light-measuring switch S1. The video back control microcomputer 50 
receives the start-up signal as an interrupt signal and thus, will 
exchange the data upon synchronizing with clock signals fed from the 
camera control microcomputer 41 via the line l2. 
The display 47 is mounted to the top of the camera body 1 as shown in FIG. 
2 and detailed indications are shown in FIGS. 3-A, 3-B, and 3-C. 
Illustrated in FIG. 3-A is an indication when all the segments and 
characters to be displayed, in FIGS. 3-B is when the film back installing 
mode is selected, and in FIG. 3-C is when the still video back installing 
mode is selected. The segments in the display 47 include generally a 
common section (PROGRAMS, TV, AV, etc) and a specific section (FIELD, 
FRAME, SVC). The numeral 55 is a counter display portion indicating 
counting numbers of the film when the film back is installed and of the 
recording tracks when the still video back is installed. In the common 
section, the characters, PROGRAM, A, B, and M are displayed when the 
programmed automatic exposure control mode, and the manual exposure 
control mode is selected, respectively. 
The character SVC (still video camera) is displayed in the still video back 
installing mode with the character FIELD or FRAME representing the field 
or frame recording mode indicated. Numbers of the recording tracks can 
also be read from the counter display 55. The common section including the 
display 55 indicates, with or without the still video and film backs 
installed, appropriate value for the respective still video back and film 
back installing modes. It is known that the film sensitivity and presence 
of a film cartridge are commonly displayed at the initial loading 
operation in the film back installing mode, which may also be utilized in 
this system. 
In addition to the aforesaid indications, the presence of a disc cassette 
or the state of white balance adjustment may be displayed in the still 
video back installing mode. 
The operation of circuits in FIG. 4 will be described herein below 
according to the flow charts in FIGS. 5 to 12. 
When the switch S1 is turned on with the release button S4 pressed halfway, 
the auto-focus control microcomputer 44 and the light-measuring circuit 42 
is energized. Instantly, a signal from the camera control microcomputer 44 
is sent via the signal line l1 thus to energize the video back control 
microcomputer 50 as well as to connect its peripheral circuits in the 
still video back 2 with the power supply. 
Consecutively, while various data information including film sensitivity SV 
is loaded, the installation of the still video back 2 is checked and the 
video back control microcomputer 50 starts exchanging the data. 
The information transferred from the camera body 1 to the still video back 
2 include the data of date or actual time to be written in the specific 
data tracks on a magnetic disk, and the exposure error data .DELTA.EV to 
be compensated. As shown in FIG. 7, this .DELTA.EV is the exposure error 
data in the still video back installing mode, resulting from a narrower 
available range of the shutter speed and diaphragm aperture in the still 
video back installing mode than that in the film installing mode. When 
less light is given, the shutter speed or diaphragm aperture value to be 
controlled will exceed the available range thereof. If the output of CCD 
is gain-controlled according to the .DELTA.EV data when the release is 
activated, the exposure error can be eliminated electrically by the 
gain-control of the CCD output. 
The information transferred from the still video back 2 to the camera body 
1 include the data representing the still video back installation, CCD 
sensitivity data aperture lower-limit data, shutter speed lower-limit 
data, field/frame selection data, counter data, warning data, and release 
inhibiting data. 
The counter data means track count numbers on a magnetic disk ranging from 
1 to 50. Every release operation counts +1 in the field recording and 
counts +2 in the frame recording. When the counting number exceeds 50, the 
warning data is transmitted to a display a warning on the camera body 
side. The release inhibiting data is sent out when the release is not 
allowed to activate on the still video back side, i.e. when the motor for 
driving a magnetic disk rotates inconstantly (at start-up), the recording 
is being made after releasing, the head is being driven, or the magnetic 
disk is just in the operation of head searching. Although the data 
exchange between the camera body 1 and the still video back 2 is effected 
at a predetermined timing as shown in a flow chart of FIG. 5, it may be 
done at a desired timing in relation to the types and properties of the 
data. 
As best shown in FIG. 5, the attachment of the still video back is checked 
after the data are exchanged and the exposure calculation will then be 
made according to the routine shown in FIG. 6 if the answer is "no" or to 
the routine shown in FIG. 7 if the answer is "yes". Then, the calculated 
shutter speed and/or diaphragm aperture value are displayed on the display 
57 together with the selected exposure control mode. 
The simbols used in FIGS. 6 and 7 are as follows: 
BV1: Brightness value provided from the first photoelectric converting 
element (SPC1) having a relatively greater light receiving area on the 
image screen of a 35 mm film, 
BV2: Brightness value provided from the second photoelectric converting 
element (SPC2) having a smaller light receiving area about the center of 
the screen, 
BVC: Brightness value applicable for exposure control, 
SVC: Film sensitivity value applicable for exposure control, 
SVF: Film sensitivity value which has been preset automatically or 
manually, 
EVC: Exposure value applicable for exposure control, 
AVC: Control diaphragm aperture value 
TVC: Control shutteer speed value 
AVmin, AVmax: Lens aperture upper and lower limit value, 
TVmin, TVmax: Shutter speed upper and lower limit value, 
SVCD: Equivalent film sensitivity value determined by the sensitivity of a 
CCD image sensor of the still video back. 
AVX: Aperture lower limit value with the still video back installed. 
TVX: Shutter speed lower-limit value with the still video back installed. 
EVX: Exposure lower-limit value with the still video back installed. 
.DELTA.EV: Exposure error value with the still video back installed. 
Center-weighted average light-measuring in the film back installing mode is 
effected, as shown in FIG. 6, such that, while the switch 43 shown in FIG. 
4 is turned to a contact position B, the first and second photoelectric 
converting elements SPC1, SPC2 produce the light measurement outputs which 
are in turn utilized for determining the brightness value BVC. Spot 
light-measuring is effected such that, while the switch 43 is turned to 
the other contact position A, only the second photoelectric converting 
element SPC2 produces the output to be used while the first photoelectric 
converting element SPC1 is short-circuited at both ends. 
During the video back exposure calculation shown in FIG. 7, the switch 43 
is turned to the A-position as set forth above while only the second 
photoelectric converting element SPC2 is activated. This means that a 
range of the light measuring is set to a small area in the still video 
back installing mode. Additionally, as shown in FIG. 6 (of the film back 
installing mode), the film sensitivity SVF is set as film sensitivity SVC. 
The exposure value EVC, the control diaphragm aperture value AVC, and the 
control shutter speed value TVC are arithmetically determined based on the 
values BVC and SVC. By comparison, as shown in FIG. 7 (of the still video 
back installing mode), the equivalent film sensitivity SVCD determined by 
the sensitivity of the CCD 21 is set as film sensitivity SVC. In the same 
manner, the exposure value EVC, the control diaphragm aperture value AVC, 
and the control shutter speed value TVC are arithmetically determined. The 
aforesaid exposure error .DELTA.EV is also calculated in the routine shown 
in FIG. 7. 
The control diaphragm aperture value AVC and the control shutter speed 
value TVC are restricted within the available range intrinsic to the 
interchangeable lens 4 and the camera body 1 as shown in FIG. 6, i.e. 
AVmin.ltoreq.AVC.ltoreq.AVmax and TVmin.ltoreq.TVC .ltoreq.TVmax. In case 
of the still video back installing mode, the lower limit of the diaphragm 
aperture value AVC is further restricted to the value AVX as shown in FIG. 
7. This results from a concept that the equivalently largest aperture 
opening of the relay optical device 19 should be examined. The lower limit 
of the control shutter speed value TVC is also restricted to the lower 
limit value TVX in the same manner. The exposure control is carried out 
based on the calculated values AVC and TVC. 
When the exposure control action is completed, the switch S4 is turned on 
thus to activate the motor for film advancing and shutter cocking. This 
motor is also activated in the still video back installing mode. While the 
switch S4 remains turned on, the tension detection can be effected to 
prevent damage to the film which is kept at tension both with its last 
frame being unable to advance. When the film advancing and shutter cocking 
are completed, the switch S4 is turned off to stop the motor. 
According to the embodiment as set forth above, the camera body 1 and the 
still video back 2 when installed are electrically connected with 
connecting terminals through which the information on the still video back 
is transferred to the camera body side so that, in either case that the 
still video back or the film back is installed, optimum mode selection can 
be made by choosing an appropriate control routine upon examining the 
attachment of the still video back in accordance with the interruption 
routine of the camera control microcomputer 41, as "yes" for the still 
video back installing mode and "no" for the film back installing mode. 
Such an optimum mode selection can also be made when the back cover of the 
camera body is closed. FIG. 8 shows an interrupt control routine for the 
case that the back cover is closed. According to the routine, first, the 
position of the back cover is examined when interruption has been made and 
then, if the cover is in its closing position, a video back start signal 
is output for the energization of the still video back and the data 
exchange between the camera body and the still video back, whereby the 
attachment of the still video back is detected. Then, the counter reading 
representing the track number of the still video back is displayed when 
the still video back is found in installation, or the initial loading 
operation intrinsic to the film back installing mode will commence when 
the absence of the still video back is recognized (i.e. the film back is 
installed). For the operation, a value n, which is assigned in a register 
installed within the camera control microcomputer 41, is reset (n=0) and 
then, the motor for film advancing and shutter cocking is driven. 
Consecutively, when the switch S4 becomes turned off as having been 
examined, the film advancing stops and the value n in increased by 1. The 
motor rotates again until the value n reads 3. When the switch S4 is on as 
having been examined, it will be examined if the time of driving the motor 
exceeds a predetermined time of advancing one frame of the film. If the 
former exceeds the latter, the loading motor is stopped while a warning 
signal is displayed. When the value n is 3 (n=3) as the film is advanced 
with its first frame ready for normal exposures, the film counter reads 1 
indicating that the initial film loading has been completed. In this 
manner, when the back cover of the camera is closed, optimum mode 
selection can be made for desirable photography whichever of the film and 
still video backs is installed. 
FIG. 9 shows a time interrupt routine in relation with an interruption per 
second for a clock, in particular. The data counted up by the second in 
the camera body 1 is transferred to the still video back side. This can 
only be effected when the camera body 1 accommodates a data imprinting 
device. 
Illustrated in FIG. 10 is a detail routine effected on detecting the 
opening of the back cover shown in FIG. 8. When the back cover of the 
camera is opened, the still video back mode is cancelled while the film 
counter becomes reset. 
Finally, the operation on the still video back will be described referring 
to the flow charts of the video back control microcomputer 50 shown in 
FIGS. 11 and 12. 
As shown in FIG. 11, when the light-measuring switch S1 contained within 
the camera body 1 is turned on, a startup signal for the energization of 
the still video back is transmitted from the camera control microcomputer 
41 to the interrupt terminal INT1 of the video back control microcomputer 
50. Upon receiving a pulse of the startup signal, the video back control 
microcomputer 50 commences the operation according to the flow chart shown 
in FIG. 11 as with energizing the video back circuit 51. The video back 
control microcomputer 50 is kept on standby until the communication start 
signal is introduced to the interrupt terminal INT1. Various information, 
e.g. film sensitivity data, is transferred to the camera control 
microcomputer 41 from which the communication start signals are in turn 
sent out. Upon receiving the communication start signal, the video back 
control microcomputer 50 starts exchanging the various information shown 
in FIG. 11 with the camera control microcomputer 41. A series of the 
communication start signals are produced periodically while the 
light-measuring switch S1 is on, as apparent from the flow chart shown in 
FIG. 5. When the communication start signal disappears, a communication 
timer will count up (FIG. 11). Then, when the timer overflows, the video 
back circuit 51 is deenergized and thus, the video back control 
microcomputer 50 will stop operating. The operation of the communication 
timer means that the video back circuit 51 can continue to operate for a 
specific period of time after the light-measuring switch S1 is turned off. 
In case that a shutter release is needed after the light-measuring switch 
S1 is turned off, it will take a considerable period of time to rotate the 
magnetic disk constantly after restarting it once the still video back 2 
is de-energized with the light-measuring switch S1 turned off, which will 
prevent normal recording of photographic images. Therefore, the 
communication timer is utilized to maintain the constant rotation of the 
magnetic disk for a certain period of time after the light-measuring 
switch S2 is turned off. The extending period of time (timer time) may be, 
although not limited to, a few seconds. 
FIG. 12 shows a flow chart for a release interruption effected by the 
camera body 1. When a release signal is transmitted through interrupt 
terminal INT2 of the video back control microcomputer 50, a gate pulse of 
the CCD 21 is cut off thus to prevent the storage data of the CCD from 
being shifted. 
While the storage data of the CCD in a TV camera is shifted every 1/60 of a 
second, the same in a still video camera has to be shifted only after the 
shutter is closed because an action of the shutter release is voluntary 
and a rate of shutter speed is not uniform. Accordingly, the shifting can 
be prevented (as the gate pulse is off) when the shutter release is 
effected and otherwise, can be permitted (as the gate pulse is on) when 
the exposure is completed (i.e. the switch S4 is turned on). After the 
switch S4 is turned on, automatic gain control AGC according to the 
.DELTA.EV data from the camera control microcomputer 41 is made on a 
signal amplifier contained within the video back circuit 51. 
Consecutively, as shown in FIG. 12, the routine divides into two branches 
for their respective field and frame recording modes of the still video 
back. 
As set forth above, there are some differences between the still video back 
installing mode and the film back installing mode and thus, appropriate 
settings for photographing relative to their respective modes are now 
apparent from the above description. The principles of the present 
invention are not limited to the preferred embodiment and other 
modifications are possible without departing from the scope of the present 
invention. 
According to the present invention, the readings in the film back 
installing mode and the still video back installing mode are alternatively 
displayed on the display of the camera body so that one single display can 
visibly indicate all the information. In addition, a switch means provided 
within the camera body is arranged so as to respond to the input 
information of signal input means, which allow a means for providing the 
display readings to be selected automatically. It will be understood that 
this principle of the present invention is most suitable to a still camera 
system which can carry alternatively a still video back or a film back. 
Furthermore, according to the present invention, the camera body 
accommodates a film back mode setting means for providing an optimum 
condition for photographing while the film back is installed and also, a 
still video back mode setting means for providing the same while the still 
video back is installed. In addition, a switching means provided within 
the camera body is arranged so as to respond to the input information of 
signal input means, which allows the mode setting means to be selected 
automatically.