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Digital slow motion cameras
Their are two types of digital slow motion cameras. Tape based systems use vhs tape to record the data.
Solid state recorders capture the data to dram, just like a computers' volatile memory.
We are adapting the latest developments in the solid state cameras for broadcast use. The new cameras will have significant improvements in both quality and speed.
High Resolution High Speed Camera
It has a 1024 x 1024 pixels CMOS sensor with 10 bit color and a 2400 frame memory,
Frame rate of 3000 frames per second at this resolution are possible
Exposures of 1/200,000 of a second are possible.
The camera is shock resistant to 100G
What is a digital slo motion camera?
It's a video camera with instant playback. It doesn't use video tape. It 's powered by batteries and is the same size and weight as a professional camcorder. The recording is digital and the resolution of the camera is better than anything before. To use it , just plug in a cable and watch the amazing world of slow motion materialize.
How Slow?
Normal PAL video records 25 frames per second. NTSC 30fps. The new systems records 100, 200, 500 1000 2000 and soon 3000 full frames per second. When one second of real time , recorded onto 1000 frames, are replayed at 25 frames per second the duration of the replay is 40 seconds. In other words, the camera stretches one second of reality into 40 seconds of slow motion. This far exceeds the capability of the Sony Super Motion system that records just 75 frames per second.
A New Approach
The advent of this slow motion video camera will encourage new ways of shooting sports. Extreme close ups that would be impossible for a camera operator to pull focus on, or would have the subject whizzing through frame can be achieved with a locked off camera. For instance, an extreme close up of the hand that releases a javelin is possible. It may take a few attempts to get the framing correct, but without the high cost of film this is not a problem. The age of hard disk storage will free the director and cameraman to try new angles and daredevil shots that won't blow the budget, or end in embarrassing failure. Shooting from cranes, helicopters or tracking vehicles poses no unusual problems.
Quality
The perceived quality of the picture by the viewer is far greater than the technical specification suggests. Recently when Television directors independently viewed the demonstration tape the common response to the question of quality was "superb''.
In fact the resolution and highlight handling ability is less than broadcast cameras, but the sheer number of frames captured per second of, lets say a gymnast, gives the viewer a picture with more detail than a broadcast camera would have achieved shooting the same subject.
What's the catch?
The camera needs 6 stops more light than other cameras. By using super fast (F1.2) lenses some of this deficiency can be overcome, but it still leaves the camera 4-5 stops slower. Outdoor events are perfect on a clear or even cloudy day and present no problem. Indoor events however, need the lighting level to be increased to at least 2500 lux. This is a similar light level to the days of tube cameras. A typical boxing ring today is lit to 1000lux. A football stadium under lights is 500-750 lux.
How the cameras work
The camera uses a special imaging device that has a higher frame rate than that of normal video. The pictures from either the CCD or CMOS chip are passed to the storage medium extremely quickly until the capacity of the memory is filled. The system is set so that the memory is continually being overwritten. That is, once the memory is full the pictures are repeatedly recorded over until the operator wants it to stop. In other words the camera can be on for every moment of a tennis match but has a limit of saving a limited number of frames at one time. The number of frames saved depends on the resolution of the chip and the frame rate. The high resolution camera can record 2400 frames, the lower resolution camera, 12000 frames.
The operator can stop the recording in 3 ways;
immediately; thus saving all the previous images in the DRAM.or middle; will continue to overwrite the first half of the existing images in DRAM with new images
or end; will carry on recording until DRAM has been completely overwritten with new images.
Once the recording is stopped the pictures are replayed from the volatile memory via the BNC video output to a VCR or microwave link or the picture can be downloaded via a output to a special data card that can store numerous scenes in original computer format. The pictures can be replayed from the camera at any speed from 1 frame to recorded frame rate without any jitter.
Capacity
The storage capacity of the high resolution camera is 2400 frames. At a replay speed of 25 frames per second this equals 1 minute and 36 seconds of playback. At a replay speed of 12.5 frames per second this equals 3 minutes and 12 seconds of playback
This may not sound like much but remember that the camera is continually recording, 24 hours a day if you wish, so consider that you are selectively saving 2400 frames at a time. The neat trick is that if nothing is worth saving then you save nothing. The downside is that the camera is out of action for the length of time it takes to replay. It is possible to indefinitely record quality slow motion, without the cost penalty of film stock
Shooting Notes
The key to the resolution of slow motion is a fast shutter speed. On a sunny day shutter speeds of up to 1/6000 of a second are achievable. On a dull day or indoors additional lighting is required. Do not despair! Consider that a 500 frames per second recording of just one second of sports action, played back at 12.5 frames per second gives you a playback shot lasting 40 seconds. The actual area that one second of sports action takes place varies from sport to sport, but it is possible to light 1 second areas, say 1 meter square, without distraction to athletes or other cameras.
As a rough guide ask your cameraman to switch in 1000th of a second shutter on your regular TV camera. This is a general guide as to weather additional lighting may be required at 500 fps.
We have developed lighting concepts and ideas for some sports that overcome the problem of additional lighting.
