Re: CCD Shutter question

Caleb J. Howard wrote:
> I apologize for the bandwidth on this question, and the crossposting.

The crossposting is ridiculous. Please do not do that!

> I will go through the IIDC spec which I have, and see what it says, but
> perhaps someone here know from experience. As the CCD is passing the

This won't be in the IIDC. It should be part of the camera documentation
to answer this or the vendor should be able to answer this question.

> pixel information down the line to Coriander, or whatever app, is there
> a blank time analogous to the flyback period of analog video? That is,
> if I am flashing a strobe, say, 100 times during a frame interval (1/30
> of a frame, for example), will the image for that frame contain all 100
> flashes, or will it lose some.

It might loose some. At least during the time it takes to remove the
charge from the cells, the CCD will not integrate image data.

> analogous to the shutter speed of a mechanical camera. I have also
> read about the differences between a rolling shutter and a global
> shutter, which also seems to pertain to the question I have.

Rolling shutter can only be found on CMOS sensors. I know of no CCD
camera with rolling shutter. Maybe with CMOS sensors it is possible to
integrate the light seamlessly.

>
> What I really hope to know is this: If I am triggering a single event
> which strobes a flash six times at millisecond intervals (for a total of
> 5/1000 - start to end), with no trigger, nor syncing mechanism - just
> capturing steadily off the 1394 bus while the event is being waited for
> - then what is the liklihood that some or all of that 5/1000 interval
> will occur during a time when the CCD is not capturing? How long may I
> keep the camera capturing, out of every frame interval. It's
> possibly/probably camera dependent, but is it reasonable to hope that a
> cheap camera (IIDC compliant) will capture all six flashes - either on
> a single frame, or accross two.

Is there a reason not to use a trigger camera?

>
> I set my cameras to 3.75 FPS, and I set the exposure to 511 in
> Coriander, and I seem to miss capturing the flashes much more often
> then when I'm running at 30 FPS. This is not what I would have guessed.

What camera model are you using? It seems like a TI chipset based
camera. This camera has no internal memory, ie. the lower data rate is
achieved by running the CCD at a lower frequency. In this mode, the
CCD/AFE might need longer to clear the charge ( where no image data is
recorded as mentioned above ).

But the real reason will be: This camera can not integrate longer than
1/30 sec, even if the frame rate is lower. To capture all the strobes,
the camera should integrate for 1/3.75 sec.

  /Arne

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Received on Mon Jan 10 09:32:11 2005