Inspired by the Strobist, I checked my 7D to be certain of the sync speed when using flash. According to the 7D manual (pages 111 and 207), the maximum sync speed is 1/250 second. That is, because the 7D uses a mechanical shutter with all its accompanying timings, 1/250 second is the fastest shutter speed that can be used with flash. For the most part, this is the case with my own 7D but there are some variations.
My G9 with its electronic shutter could be used up to about 1/2500 second sync speed provided it did not know much about the flash that was attached. To take advantage of this odd behavior, I often used a Nikon SB-28 with the G9.
Before going too much further, yes, I am aware that the Canon flash system can operate in “High Speed” mode at shutter speeds faster than 1/250 second. However, High Speed mode uses pulses of light and the net lighting power is significantly reduced. Yes, High Speed flash mode works and is useful but the name of today’s game is syncing the 7D to that single burst of light when the camera is in normal flash mode.
The first clue to 7D flash sync occurs when using the built-in popup flash. There’s no way to set a shutter speed above 1/250 second. Also, there’s no High Speed mode for the popup flash. On the more positive side, at 1/250 second, the light appeared to be fully distributed over the shutter. Well, at least that experiment was easy.
Next, I tried a Canon 580EX, 420EX and 380EX. All acted similarly with respect to sync speed. The 1/250 second shutter speed combined with flash produced even lighting but faster apparent shutter speeds reverted to 1/250 unless the flash was placed in High Speed mode. I even tried the 580EX in full manual mode with the same results: 1/250 second is the fastest available shutter speed.
Time to try the Nikon SB-28. It syncs at 1/320 second! At 1/400 second there was a dark edge at the bottom of the image. About half the frame was dark at 1/800 second.
What about wireless? My cheap Cactus wireless triggers at 1/500 second on my G9 and, on a good day, even 1/640. Those same units are limited to 1/200 second on the Nikon SB-28 and Vivitar 285HV when used with the 7D.
I’ve been using the 7D popup flash to trigger the 580EX and really like this combination; however, the maximum sync speed is 1/250 second because the popup cannot operate in High Speed mode.
So the 1/250 second limitation is basically true. Oh well, if necessary, I still have the G9.