What is X-sync?
X-sync or flash sync refers to the highest shutter speed which can safely be used with flash photography on a given camera model. This can be as slow as 1/90 sec on low-end Canon cameras to 1/250 on high end film cameras or even 1/500 sec on the EOS 1D digital camera. The flash sync problem occurs because of the way focal plane shutters used in most SLR cameras are designed. Such shutters contain two travelling curtains which open briefly to expose the film or image sensor. At slower shutter speeds the entire image area is exposed, but at higher speeds an interesting trick is used. Rather than exposing the entire image area in one go the two curtains form a moving slit which travels the length of the image. With ambient light exposure this isn t a problem, since the lighting will remain constant as the slit travels across the frame. However, flash exposure is a problem since the subject-illuminating burst of light from the flash is so brief. If flash is used in conjunction with a high
