Photography – Camera release control circuit
Reexamination Certificate
2000-10-13
2002-10-08
Gray, David M. (Department: 2851)
Photography
Camera release control circuit
C396S265000
Reexamination Certificate
active
06463215
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a system for sequential triggering of cameras and picture taking equipment equipped with the said system.
Within the framework of the invention, a camera refers to a still camera for taking frame by frame type pictures, in opposition to movie cameras designed for “continuous” recording of pictures. For example, it may consist of a reflex camera or a compact 24×36 camera, or even optionally a digital camera.
The invention is used for applications in the photography of fast phenomena, particularly for applications related to ballistics, “crash test” type impact studies, movement analysis in sports events, or the study of the trajectory and dynamics of a projectile for example.
STATE OF PRIOR ART
Most modern cameras, and particularly reflex cameras, are provided with an operating mode called “burst” mode. In this operating mode, the camera continues to take successive views for as long as the trip device is activated. Successive views are recorded at the maximum rate possible for the camera. This is controlled mainly by the film advance device installed in the camera.
For example, burst operating mode may be used for the photography of sports events. It is capable of capturing several pictures per second, with a maximum of 6 to 8 pictures per second depending on which camera is used.
However, this rate is insufficient in some applications.
A higher picture taking rate is possible if a “continuous” recording camera is used, such as a movie camera or a video camera (camescope). Therefore, cameras are capable of collecting fast phenomena or events and enabling a better decomposition of these events in a sequence of instantaneous pictures.
However, the quality of pictures taken by “continuous” recording cameras is very much lower than the quality obtained using frame by frame type cameras and is often insufficient for a detailed analysis of a sequence of individual pictures.
Equipment is also known in which several cameras are installed in sets and are computer controlled in order to achieve a trigger rate faster than the burst mode rate of individual cameras. Further information about this subject is given in documents (
1
) and (
2
), the references of which are given at the end of this description.
There are several limitations or difficulties with equipment using a set of cameras.
A first difficulty is due to the need to transform or reconfigure the trigger system when the number of cameras used in the set is modified. Exactly the same problem occurs when cameras with a different picture taking rate in burst mode are used.
Another difficulty is due to the fact that in burst mode, cameras usually finish the number of pictures available on their film very quickly. Therefore, the film has to be changed for each new series of pictures taken. It may be difficult or even impossible to make this film change when taking pictures in a hostile environment. Replacing the film in all cameras is also an expensive operation in terms of time, and requires a relatively long interruption between successive series of pictures taken.
Another difficulty arises when triggering cameras. An operator has to be present and equipment must be installed close to the subject to be photographed. These constraints can cause difficulties when taking pictures in a hostile environment.
DESCRIPTION OF THE INVENTION
The purpose of the invention is to propose a sequential trigger system and picture taking equipment largely to avoid the difficulties mentioned above.
One purpose in particular is to propose a sequential trigger system that can be used with a variable number of cameras and for different rates of taking pictures in each camera.
Another purpose is to propose a system for recording several series of photographs without systematically replacing the films in the cameras.
Yet another purpose is to be able to control cameras from a location remote from the subject being photographed and to be able to servocontrol cameras to a specific event, for example such as firing.
More precisely, in order to achieve these purposes, the objective of the invention is a system for sequential triggering of several cameras equipped with a burst mode. The system comprises:
a clock and means of fixing a clock frequency for the said clock as a function of the number of cameras to be controlled by the system and/or as a function of the rate at which cameras can take pictures in burst mode,
means of successively starting the operation of the cameras in burst mode in response to a trigger signal, the means being controlled by the clock so as to put the cameras into operation at an operating rate faster than the picture taking rate of the cameras in burst mode.
Since the operating rate is faster than the picture taking rate in burst mode, the cameras are triggered in turn so that a fast global picture taking rate can be achieved.
The clock frequency may be fixed and optimized such that the operating rate denoted Cs is equal to N×Cr, where Cr and N are respectively the rate at which the cameras take pictures in burst mode, and the number of cameras controlled by the system.
The operating rate is also equal to the global rate at which pictures are taken by the set of cameras controlled by the system.
For example, the camera operating rate and the global picture taking rate Cs is equal to 48 pictures per second, if six cameras are used with a rate Cr in burst mode equal to 8 pictures per second.
Means of fixing the clock frequency can be provided so that the structure of the trigger system can be instantaneously adapted for use with a variable number N of cameras and an arbitrary rate Cr at which the cameras used are triggered in burst mode, without changing the structure of the trigger system.
In this case it is assumed that all cameras used have practically the same trigger rate in burst mode.
The clock frequency is preferably fixed at a value that is a multiple of the product Cr.N, in other words a multiple value of the rate Cs mentioned above. Thus, cameras can be put into successive operation with better time precision.
According to one particular aspect of the invention, the trigger system may also comprise a timer to fix the total picture taking duration and to suspend operation of cameras when the total fixed duration has expired.
Events to be photographed with a high picture taking rate are typically transient events or fast events for which the global duration does not exceed a few seconds.
Thus, using the timer, the series of pictures being taken can be interrupted before the reel of film installed in each camera is finished, and a new series can be restarted again later.
For example, if the cameras used have a picture taking rate in burst mode equal to 8 pictures per second, and if the total picture taking time is fixed at 2 seconds, two series of pictures being taken (16 pictures per series) can be recorded on a standard film for 36 pictures.
If the time is fixed at less than the time necessary to complete the film, several series of pictures can be taken without reloading the cameras. This is an important advantage for taking pictures in a hostile environment, for example in studying projectiles, or for correcting a firing defect.
According to another aspect of the invention, the trigger system may include means of outputting a trigger signal and remote transmission means for transmitting the trigger signal to an input triggering the trigger system.
In their simplest embodiment, the means of supplying a trigger signal may comprise a single trigger switch that can be operated by an operator and designed to close an associated trigger circuit.
These means may also comprise a countdown device, for example similar to devices used for firing projectile engines.
Thanks to the remote transmission means of the trigger signal, the system can be used in an hostile environment in which the presence of humans is impossible. It can also be used so that heavy equipment can be installed in a location remote from the subject being photographed.
For example, the transmission mea
O'Connolly Patrick
Toineau Michel
Aerospatiale Matra Missiles
Gray David M.
Krebs Robert E.
Thelen Reid & Priest
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