External auto flash stops high speed sync

The more you explore what your gear can do the more you find out things that work, and those others that don’t. Today’s tip is all about external auto metering (thyristor mode) on the Speedlite 600EX-RT.

If you are using external auto metering with the Speedlite 600EX-RT then you cannot also use high-speed sync flash.

I ran in to this when shooting using my preferred group mode set-up. I tend to set Speedlites that light the background in External Auto, once the light is at the required level it keeps being consistent since the light to background distance is the same and the reflective quality of the background doesn’t change from shot to shot either. Lights in a different group might be in manual or E-TTL modes, but you cannot have high speed sync – the flash set to external auto cannot do HSS on it’s own or as part of a bigger lighting set-up.