Sorry, posted in a wrong forum, I wanted to post it on Magic Lantern forum
Canon is actually blocking any shutter speed higher than X-sync if flash hi-speed sync is not turned on (or not supported)
some third party remote trigger is cheating the camera, that the attached flash do support hi-speed sync, so the camera allows choosing shutter higher than X-sync.
In such setup, the flash unit works normally as a ETTL flash without hi-speed sync, pre-flash, metering and fire just normally (as a flash with no hi-speed sync). The camera thinks the flash is hi-speed sync enabled, pre-flash, metering and trigger the flash as if it is a hi-speed sync flash.
the benefit of this is we got ETTL flash metering, better flash reach as the shutter is higher, use less flash battery power as hi-speed sync is eating a lots of power.
the drawback is we might see a dark shadow at the bottom of the frame, it is the second shutter curtain blocking the flash light.
For 60D, the X-sync is 1/250. Hypersync at 1/320 will give a very thin shadow at the bottom, almost invisible. Hypersync at 1/400 will shows a wider shadow, but if used carefully, avoiding foreground object be in that area, it is totally usable.
I am not sure how this can be done with ML. can it force the Flash settings of shutter sync to hi-speed sync? even if the flash is not supporting hi-speed sync.
Or overriding the shutter after flash metering is done? so that camera set the shutter at 1/250, then preflash, then meter, and before the camera actually start taking the picture, ML overrides the shutter to 1/320. The flash is triggered and shutter works as 1/320.
Another function I am dreaming is the second curtain Hypersync. When using hypersync, there will be a dark shadow at the bottom of the frame, which could be annoying when shooting daylight scene with people. If hypersync can sync with second curtain, the dark shadow will be at top of the frame, which usually is distant background or sky in the scene. So the dark shadow is essentially no visible.
