>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.
That's NOT a bug, and if you think about it, it's the only way they
can make focal plane flash work for shutter speeds greater than the
inherent electronic flash sync speed of the shutter... as the
curtain opening travels across the film plane, the flash fires
MULTIPLE TIMES so that every portion of the frame gets the same
flash exposure. It has to fire once for every width of the curtain
opening as the slit progresses across the film plane.
That's why the flash range decreases so much in FP/high-speed sync
mode, due to the multiple discharges.
The basic flash synch speed is the fastest one at which the shutter
curtains are fully open and expose the entire film frame
simultaneously... any faster than than, and the shutter opening is a
slit travelling across the film plane formed by slightly offsetting
when the first and second shutter curtains open.
All that is well known to anyone who uses flash.
The fact that FP mode, or HS mode is still active when the shutter
speed drops to the X-sync speed is definitely a bug, an undesirable
feature or whatever you want to call it. Gerard's points are well
made and fully valid. At the x-sync speed and below standard
operation, ie, short duration should be effected, as it gives you
many more options and is considerably more efficient.
--
* Henning J. Wulff
/|\ Wulff Photography & Design
/###\ mailto:[EMAIL PROTECTED]
|[ ]| http://www.archiphoto.com
*
****
*******
***********************************************************
* For list instructions, including unsubscribe, see:
* http://www.a1.nl/phomepag/markerink/eos_list.htm
***********************************************************
