Re: CCD Shutter question

Arne Caspari wrote:

> Caleb J. Howard wrote:
>
>> I apologize for the bandwidth on this question, and the crossposting.
>
>
> The crossposting is ridiculous. Please do not do that!

OK. I generally wouldn't, but I got no reply when I previously had
posted less broadly.

>> 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.

The vendor is Unibrain... This was not my first choice, (I called the
Imaging Source first) mostly because of your sound-seeming advice, but
alas, they were the *only* vendor able to ship me product in the time
frame I needed it. I will call them tomorrow, but their technical and
sales people were pretty much unable to answer the much more basic
questions I had for them when I was ordering the cameras.

>> 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.

This was my assumption.

>> 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.

Ahhh... This would explain why only a few places even mentioned rolling
shutters. Thanks for the clarity on that.

>> 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?

Availability and cost, mostly. I would have *loved* to get ahold of a
couple of those 21BF04, but I guess they're not available yet.

>> 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 ).

I have the Unibrain Fire-i400 industrial.

> 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.

Is this so because no camera can integrate >1/30 second, or because
this is a limitation of the TI chipset? Whichever, my solution would
then at least partially be to increase the frame rate to 30 FPS. I
gather from the Coriander "exposure" feature that the shutter can be
set, within limits. I'll call Unibrain again, and ask them what the
maximal exposure would be. I can handle some loss, if it's not extreme.

I'd much rather have a trigger camera, though. I'm still trying to
source cameras better suited to my purpose. I'll be calling Shane
Jennings (at the Imaging Source US) again tomorrow.

Thanks again!

-caleb

=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-
 Caleb J. Howard - calebh@adelphia.net (home) - caleb@rhythm.com (work)
      http://howards.vigilante.net/Caleb/Personal/CalebMain.html
      'It was for this you were called, created, formed and made.'
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Received on Mon Jan 10 10:14:25 2005