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High-speed sync
Some facial expressions demand a full aperture setting even when backlit by the sun.
image:High-speed sync
High-speed sync     EF135mm f/2L USM, E1/750, f/2
Sample photo analysis
image:Daytime sync
Daytime sync
The main photo was taken in the FP high-speed sync flash mode with a fully open aperture, while the other photo was taken in the normal daylight fill-flash mode, which required a slower shutter speed and smaller aperture. In both shots, the creative objective was to highlight the girl's facial expression by blurring the house and background objects as much as possible. As you can see, the level of blur is much more impressive in the main photo.
High-speed sync flash achieves beautiful blurring even when shooting against the sun.
When subjects are backlit by the sun, strong shadows tend to mask facial features and other details. Photographers can eliminate such shadows by readjusting the exposure, but this form of compensation is likely to overexpose the background. Another possibility is daylight fill-flash. This technique is often effective when shooting outdoor portraits because it illuminates dark areas of the subject and strikes an excellent balance between the brightness of the subject and background. However, its range of uses is limited because the shutter speed cannot be set faster than the X-sync speed of the flash and the aperture must be reduced to compensate for higher brightness.

EX Series Speedlites offer the perfect solution. When used in combination with the FP high-speed sync flash mode, EX Series Speedlites can synchronize with a shutter speed that is faster than the camera's flash X-sync speed. This availability of faster shutter speeds allows the aperture to be set more freely. And when a large-diameter EF lens is additionally used, the aperture can be fully opened to achieve beautiful blur effects.
Flash synchronization at all shutter speeds enables larger aperture settings.
When fast shutter speeds are selected, the second shutter curtain begins closing before the first curtain fully opens. The illumination therefore only hits part of the film at normal flash settings. But the FP high-speed sync flash setting fires repeatedly at roughly 50kHz intervals during the exposure to achieve flash synchronization at all shutter speeds. The camera automatically reverts to normal flash firing when the shutter speed is set slower than the flash X-sync speed.
High-speed sync
A tip on high-speed flash synchronization
・ Use Aperture Priority AE (automatic exposure) mode
When shooting in the Full Automatic or Program AE (P) mode with a mounted Speedlite, an EOS camera automatically sets the shutter speed and aperture for typical daylight fill-flash photography. Switching to the Aperture Priority AE (Av) mode allows shooting with the aperture fully open.
High-speed sync Wireless multiple flash
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