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When trying to freeze a person in motion at several positions, I discovered some synchronization issues with the Speedlight’s stroboscope mode when using several flashes.

I use two flashes: an SB-900 and an SB-800. They’re not firing exactly at the same moment. It seems like the more often the flashes are to fire, the delay of one of the flashes increases. In my tests, the SB-800 was always the second one to light up, but I’m not sure whether this is due to the model’s age, it’s (slightly) more distant position to the camera or something else.

First attempt with the SB-900 hooked up as master on the camera For the first attempt, I hooked the SB-900 onto the camera and set it to master mode. The SB-800 was placed about 2 meters left from the camera. As you can see from the picture, the more times the flashes light up, the delay increases.

For the second attempt, I placed both flashes onto a Yongnuo wireless receiver and set them to “local” (no remote) stroboscope mode. When I attached the transmitter onto the camera’s flash socket, both flashes only fired once. So I detached the transmitter again and pushed both camera and transmitter trigger separately by hand without releasing the transmitter’s button for some seconds. With this method, when both flashes were set to a frequency of 4Hz and flashing up 4 times, the result was pretty good. The contours of the moving ball were really clear. But the more I increased the frequency and the number of times to flash, the more unclear did the ball’s contours get.

Both flashes triggered from a Yungnuo wireless transmitter/receiver

I understand that even light needs some time to cover distance, but with the speed of light the difference between the flashes positions and the moving object shouldn’t come out that clear as in these example shots.

If anyone has an idea how to solve that synchronization problem, I’d really appreciate that.

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    Light travels 299,792,458 meters in a second - so I don't think it's the speed of light that is causing your problem.. – dav1dsm1th Feb 25 '14 at 23:27
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Put only one of the flashes in strobe mode; set the other to SU-4 slave mode (on an appropriate low manual power setting) to allow it to be driven by the strobe mode flash. There will be a slight delay, but it'll be measured in microseconds and shouldn't affect apparent simultaneity unless you're dealing with something a lot faster than basketball players.

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