> -----Original Message----- > From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of Gerard Maas > Sent: Thursday, May 10, 2007 5:07 PM > To: eos@a1.nl > Subject: EOS 5D High Speed Flash Sync Mode - potential bug > > Hi all, > > While doing some 'frozen flash' images I discovered some unexpected > behavior of the EOS 5D: > > Some background first: > > FP Flash, also known as High Speed Sync and denoted with the H(Bolt) > icon is normally used for fill-in flash in bright conditions where > your shutter speed exceeds the XSync limit (1/200 on the 5D). That way > you can keep using wire apertures to achieve a nice background blur > and still flash your subject for fill-in. It actually works by firing > a seemingly continuous beam of light for the length of time that the > shutter is open (avoiding in that way the banding that you would > observe otherwise). This feature requires a much higher energy output > than normal flash and therefore your flash range is dramatically > reduced. > > Well, all this bg info is to be able to explain the bug in simple terms: > > Even when FP Flash mode is active on the flash (H[bolt] icon active on > the flash LCD or red led lighted up on the ST-E2), the FP mode should > only activate when your shutter speed exceeds XSync speed. The > problem I found is that the 5D is activating the FP mode also when > used at XSync speed. This behaviour is unexpected and certainly > undesired, given that it will dramatically affect flash exposures. It > reduces the flash range, increases recycle times and consumes > batteries faster. > > To make it very concrete: If you have FP flash active on the flash and > your shutter speed is 1/200, the flash will fire in FP flash mode > (also called 'long burning'), so instead of having a typical flash > duration of 1/10000, the flash will fire for 1/200, an exposure 5x > longer! > > The tricky side of this bug is that there's no apparent visible > difference between normal flash and FP flash. You can only observe > this bug by photographing a rapidly moving subject, like running > water. In my case I was photographing an hourglass running and noticed > the bug when I was unable to freeze the sand grains falling, even with > the lowest flash power setting (that is supposed to have a duration of > about 1/35000 of a second) > > I've submitted this bug to Canon and I'm still waiting for a response. > It would be nice if some of you, using an EOS5D and a Speedlite could > try reproduce the problem. That way I will know if it's only an issue > in my camera. > > You can see the images that triggered the whole story on my blog: > http://www.gerardmaas.net > > greetz, Gerard.
It sounds to me that the flash is doing exactly what it's supposed to do. My 550EX manual (p32) makes no mention of the flash shifting to non-FP mode when the shutter speed drops to (or below) the X sync speed. To me, the bug is that the H in the viewfinder disappears when the shutter speed is set to (or below) x sync, even though the flash will still fire in FP mode. Tom P * **** ******* *********************************************************** * For list instructions, including unsubscribe, see: * http://www.a1.nl/phomepag/markerink/eos_list.htm ***********************************************************
