High Speed Sync with Canon 430 EX II

[Justin]

Does the high speed sync work on ALL shutter speeds or just a specific range?

I was photographing a picture of my dog with my Powershot G12.  I used a shutter speed of 1/500.  It was slightly too dark so I went with a shutter speed of 1/400.  The results were almost exactly the same, so I went down one more setting to 1/320.  This time when the flash fired the amount of light was so bright that I could not see anyting.  It was so overexposed that my screen was almost completely white.  I set the manual flash output level to 1/8 to get the correct amount of light.

All other settings on the camera remained unchanged as well as the distance from the subject.

[7D5D]

HSS works above your camera's sync speed up to 1/8000.   I don't  know the sync speed on your G12 but maybe you dropped to sync at 1/320.  Most dSLRs are 1/200 or 1/250 sync speed but since the G12 has a smaller sensor, the sync speed could be 1/320.

Your flash effectiveness takes a huge hit when using HSS.   Before your first shutter curtain is fully open, the second curtain is already beginning to close.  So with HSS, your flash is firing very rapidly illuminating that small shutter opening as it travels across the frame.  The power that would be used for a single flash burst, now has to be divided among those thousands of bursts.  With that being said it will necessary to increase your ISO or aperture opening to obtain adequate exposure for high speed shutter shots.

Edit:  the sync speed for the G12 is 1/250

[Justin]

Thanks for the reply.  I went back and did some more test shots and found out that at 1/250 there is sigificantly more light, so that must be where it dropped from HSS.  The manual stats that the flash can synchronize with all shutter speeds.  This is a little bit misleading since the HSS only happens when the shutter is above 1/250.  The flash keeps the HSS icon present even when you drop your shutter speed to 1/250 & below.

I have been leaving the HSS icon on all the time knowing that if I need it then it will occur, and if I drop below 1/250 then the flash seems to operate normally as if it HSS is not enabled.  If I turn off the HSS icon, then the flash will override the shutter speed even if I have the camera set to manual.  I took a few pictures with the HSS off and set my shutter speed to 1/2000 to see what would happen.  When I took the picture my shutter speed automatically dropped to 1/250.

Justin