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How have I managed to record fill flash beyond the cameras synch speed???

AlHareAlHare Member
edited March 2012 in flash & lighting
I did a shoot recently where I shot a lady cooking food over a table on a beach at sunset. I used fill through a shoot through brolly via a 580EX11 fired by my Skyport. My settings were ISO400, f4 at 1/320. I achieved well lit results but it occurred to me that this should have been a complete disaster-why on earth didn’t the second curtain ruin my images? My camera is really only good to 1/160 synch when i've tried it out in a studio situation where it's all flash light, no ambient...

The flash was on Manual-probably 1/4 or 1/8 power and no HSS.

I posted this issue in the EOS Magazine Forum run over here in the UK and a reply has suggested that as the light was used as fill only, it is not affected by the second curtain, whereas it would have been had the subject ben lit principally by the flash, as per Neil’s results above in the studio set up which is ambient free.

I’m not convinced yet-it’s like defying the laws of gravity to say a flash can properly illuminate (or in this case fill light) a subject when fired with shutter speeds beyond the camera’s theoretical synch speed! And it’s driving me nuts now…


  • TrevTrev Moderator
    edited March 2012

    I think it's merely the fact that the image of the person is central and the second curtain shadow did not affect the outcome of it at all, and yes, a lot of ambient was in the equation.

    You ended up with a result so go with it. :)


    EDIT: Here is an interesting article:
  • Neil vNNeil vN Administrator
    Exactly what Trev said.

    David Ziser has turned this into a technique, by rotating the camera upside down, to get the flashed part of the image to be that where the subject is.

  • Trev, Neil; many thanks for your input. Trev's link in particular is of a level of technical complexity that I'll need to sit and apply my mind to it with a cold beer for company one evening!

    What I'm still not 100% clear on is how the off camera fill flash has been able to time itself to go off during the 1/320 exposure. I thought that if the max synch speed was 1/200 it would mean the flash could not be accurately timed to fire at the same time as the shutter was opened?

    BTW, anyone reading should understand the distinction between this fill flash synch issue I'm raising and the issues posed by Neil in: http://neilvn.com/tangents/2009/06/23/going-higher-than-max-sync/ where full manual flash power is used to 'beat' the synch speed limitations.
  • Alhare,

    This is a vertical shot witch means that at 1/320 of a second your only 1/3 stop over ur max sync speed (2/3 if ur max sync is 1/200 of a sec). lets say u had this exact setup indoors with no ambient, only about 1/5 of the photo will have a black bar on the right side of the photo, in ur paticular situation ur flash was only lighting the lady not the background, and the lady is positioned in the middle of the photo so she is getting the full effect of the flash,

    one way to test this would be too take a a shot of a blank wall indoors at 1/320 with flash and see how much of ur frame becomes blocked by the the return shutter then if u match that up with the above photo u can determine if going above the sync speed should have affected the flash illumination on the subject
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