Why do I get horizontal grey bar with flash at shutter speeds slower than max sync speed?

Question

I'm a total newbie to flash photography. And I just trying to do some test shooting with Canon Speedlite 580 EXII using my 7D.

I saw on the user manual that the maximum sync speed is 1/250 sec.

However I got the horizontal grey bar on shutter speed 1/200 and even 1/160 !

I would like to know what I did wrong... PLEASE HELP ME OUT !

See the images here:

Thank you!

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I have this issue with Cactus V5, as well as pocket wizard plus II, With Pocketwizard Mini TT1 and Flex TT5 I dont have that issue maybe because of the high speed sync support ?

Thank you for all the helps !!!

Answer

The 580EX should be fired in perfect sync with the 7D. Definitely when below sync speed. You seem to have a lag in your system here so the flash fires a fraction of a second after the 2nd curtain starts to close.

UPDATE - just noticed that the flash is actually mounted on the light stand and shoots through the umbrella - and it looks like you are using a non TTL wireless trigger to fire the flash. In this case it is possible that the radio trigger introduces that lag.

UPDATE 2: You can try setting the trigger to 1st curtain if it is set to 2nd curtain and it may help overcoming this lag with the slower shutter speed (say, 1/160).

I wonder why you don't use the built in remote flash controller in the 7D? The 580EXII+7D are a (almost*) perfect match in this sense.

(*) almost, b/c it does not support high-speed sync (HSS) mode in wireless mode.

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