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DBKooper
August 10, 2007, 07:41:54
I am trying to capture a remarkably short event in a science experiment. When the specs call for 15 frames per second, how much time is actually used each second for recording a frame, and how much "down time" is there for the capturing process ? If, for example, the capture at 15 fps required using the shortest actual exposure time of 1/10,000th of a second, then there would be 9,985 out of 10,000 when the camera would effectively see nothing, because it would be presumely transmitting out the information and resetting itself.

On the other hand, if the camera could be adjusted to be open, say 6 one hundreths of a second for 15 times during a second, and the remaining 10 one hundreths of a second was devoted to transmitting the information and getting ready for the next shot, then the odds of capturing an ultra short event would be 9 out of 10.

I hope this is clear, but I realize maybe it is not.

In a nutshell, is the 15 frame per second dependent on the ultrashort shutter speed, or can you adjust the shutter speed to between a quarter and a sixth of a second and still get a 15th of a second frame rate ?

Does the camera output 15 frames per second continuously ? Or does internal memory fill up at some point ?

What is the maximum firewire speed for the camera, and does it require that speed to achieve the 15 fps rate ?

We are considering purchasing a couple of these or a more expensive camera if this one does not perform as we need it. Any suggestions for a more expensive camera that will do these tasks ?

Can the camera software be adapted as part of a control chain, software or hardware, so that an event external to the camera sets it in motion ?

thanks in advance for your thoughts,

DBKooper

Tim Cassens
August 13, 2007, 17:04:04
Hello DBKooper

The exposure/transmission of the camera works in two different modes, depending on both the selected frame rate and the exposure time.

If the exposure time is less than or equal to the frame interval (1/fps), the images are captured and transmitted simultaneously. The transmission speed is determined by the frame interval. The data is split into small packets and transmitted so that multiple cameras can transmit over the same 1394 bus at low frame rates at the same time. The exposure of the next frame is started while the transfer is still running, so that the next transfer can begin as soon as the exposure period is complete.
If the exposure time is ~66ms, and the frame rate is 15 fps, the camera is capturing and transmitting simultaneously all the time.

If the exposure time is greater that the frame interval (e.g. 70ms for 15 fps), the camera enters long exposure mode. Because of technical reasons, a simultaneous transmission and exposure is no longer possible. Instead, the image is captured and then transmitted. The next exposure starts once the frame has been completely copied to the host computer.

The DBK 41AF02.AS camera takes up 64% of the available firewire bandwidth (running 1280x960, Y800, 15 FPS).

Best regards
Tim Cassens