Because the important time is when the image is acquired, not when it reaches the computer. The spacing between your images is ALWAYS the same.
I would be willing to bet that if you use an external trigger, your timing would get just a tiny bit worse, not better. Instead of precise digital timing, you would be using an analog waveform (even though it looks digital). Analog signals can easily be corrupted by noise and other external influences.
If you really feel you need to prove the repeatability, your only true option is to use a counter/timer to measure the spacing of each pulse. I can't think of any other way to do it (other than variations on the theme, such as a scope).
Perhaps the camera manual would talk about how repeatable the timing of the camera is. Manuals often have useful information like that.
Bruce
Bruce Ammons
Ammons Engineering
