On Wed, Jun 3, 2009 at 3:50 PM, Dave Tweed wrote: > Youda He wrote: > > On Wed, Jun 3, 2009 at 2:33 PM, Dave Tweed wrote: > > > I built an apparatus to measure the latency from the time of the > > > contact closure to the actual exposure. By default (autofocus, etc.), > > > it could be anything up to 400 ms, sometimes even more. We fiddled > > > around with the camera settings, and by turning off all the automatic > > > features and engaging the mirror lock-up, we were able to get it down > > > to about 40 ms +/- ~5 ms. > > > > > > These experiments were with the Canon EOS Rebel XSi (12 Mpixel), but > > > we'll be using the newer T1i (15 Mpixel) in the actual pod. > > > > How do you measure the synchronization? we use a micro controller to > > check the flash trigger signal. > > By looking at the picture! > > The apparatus is a microprocessor with 40 LEDs arranged in four groups of > ten. Each group has one LED on at a time. The first group advances every > 100 ms, the second every 10 ms, the third every 1 ms, and the last every > 100 us. By seeing which LEDs are lit in the captured image, you can get a > pretty good idea (within a few percent) of the start and stop times of the > exposure, up to 1 second, with 100 us resolution. > > A 41st output turns on the BSS138 trigger at time zero. > > I used a PIC32, mainly because I had an eval kit sitting on my desk, it has > enough I/O to drive all of the outputs directly, and I had already built a > suitable breakout board that could hold the LEDs. > We use a micro controller to read the flash trigger signal, when the last one arrives, we trigger the flash. (hope the first one shutter is still open), Nikon cameras are pretty consistent, Pentax is not, Canon is pretty good as well. Have not really measured the timing, but seems to work well at 1/150 second exposure. -- Youda > -- Dave Tweed > -- > http://www.piclist.com PIC/SX FAQ & list archive > View/change your membership options at > http://mailman.mit.edu/mailman/listinfo/piclist > -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist