Question about the clock signal vs. the shutter

[wwuser]

Hi, my team and I are working on a project involving C120 cameras. Since this camera operates at 120Hz, thus an image is capture every 8.33 milliseconds.
1. My first question is during that 8.33 milliseconds, how long does the shutter stays open.
2. How is the shutter opening related to the SYNC signal (at positive edge, negative edge?)

Sorry in advance if I violated any forum rules, it is my first time to post a subject.

more importantly, thank you in advance for any input.

[Birch]

To calculate the exposure duration for a C120 camera use the following formula :
(exposure setting / 400) * (1000 / 120) = time in ms

In the case of the default exposure (200), it would be :
(200 / 400) * (1000 / 120) = ~4.16ms

Please see the following post for additional information about SYNC.
http://forum.naturalpoint.com/forum/ubb ... #Post28456

The C120 uses a rolling shutter, so the exposure timing for a given pixel is more complicated than for a camera with a global shutter (such as our V100). You may want to do some reading about rolling shutters online if you aren't familiar with their behavior.

[wwuser]

In terms of the rolling shutter, if we want to capture 1 laser point during 1 frame, all we need to do is to make sure the laser point stays on during the exposure time, right?

In terms of the relationship between when the rolling shutter starts capturing image and the sync signal, since C120's sync is active low, does that mean the shutter will start at the negative edge of the sync signal and finish capturing the image at the positive edge of the sync?

[Jim]

Hello:

Rolling shutters do not work very well to capture pulses of light. Basically, only a few lines are exposed at a time, and that "rolls" down the image like a blade. The only way to make sure you capture the light pulse is to keep the exposure at about the number of lines of the frame, so around 400 or so. You can go with less, but you risk the pulse of light only being exposed to certain lines, you will see it as one part of the image showing a much brighter part than the rest, from the top down. During Vertical Blanking, most rolling shutter imagers do expose the entire frame for a brief period of time, but you have to find that window, that is the only trick I know. You could use a 555 timer, and then offset your pulse based on the sync signal to find the ideal timing, that is what I recommend.

Global shutters work much nicer for this purpose, as they expose the entire frame at one time, for a defined amount of time, so you can get the signal to noise ratio much higher, which is what I assume you are trying to do.