whats the difference between them. if a flash is capable of FP flash at high sync speed why should one worry about his body not giving a high shutter speed with flash on, for ex. Rebel 2000 has a X-sync of 1/90sec but even with a 380EX one can go upto 1/2000sec in high speed sync mode. i always wonder about this because in many reviews on R2K its low X-sync is mentioned as a weakness.

thanks

-- sajeev (chack74@yahoo.co.in), March 11, 2002

Answers

In FP mode, the flash has massively reduced range as compared to standard X-sync. There are other situations where X-sync is useful (studio work, macro work, etc).

-- Isaac Sibson (isibson@hotmail.com), March 11, 2002.

When you use regular flash with X-sync you're using a very rapid pulse of light from the flash unit. With FP mode flash you aren't - the flash is pulsed and so the duration of the flash pulse is stretched out over a longer time period.

This has two main consequences. First, as has been pointed out, the distance range of the flash unit in FP mode is going to be lower than in regular mode, because the pulsing lowers the total brightness. Second, you can't use the flash for freezing motion as well since the duration of the flash pulse is longer. For that reason "high speed sync" flash is a somewhat confusing and possibly misleading name for FP flash.

Another issue is that the top shutter speed of the camera is also limited to the X sync speed when you're using an external flash unit that doesn't support E-TTL, such as a studio flash unit. Remember as well that the camera's internal flash unit does not support E-TTL either. No Canon internal flash unit on any camera supports FP mode flash, even on those cameras (D30, D60) which support E-TTL.

This stuff is detailed in my EOS flash document. http://teladesign.com/photo/

-- NK Guy (tela@tela.bc.ca), March 11, 2002.