stevelee said:Since we have raised the issue of flash sync, can somebody quickly comment on the fast flash sync feature? I’ve never used it, and frankly don’t know when I might want to or why. I don’t use flash a lot as it is, but might do more if I knew more what I was doing. How well does the fast sync work and under what circumstances?
I now have a 6D2, and haven’t noticed this feature in instructions for any previous camera of mine.
If you use regular flash sync, as you set your shutter speed goes faster than 1/180 to 1/250 (depending on the camera), an increasingly large portion of the bottom image will be blacked out, because of a "rolling shutter".
Without getting technical, to get around that, a high speed sync (HSS) flash rapidly fires in succession (so fast that it just looks like one flash to the human eye). It works great, with the downside being that it is much less powerful than a single flash. HSS will let you set your shutter all the way to 1/8000, which is faster than your 6DII supports.
Under normal circumstances, especially indoors, if you want to illuminate your subject, you'd never fiire a GN60 flash (like the Canon 600EX-RT) at full power anyways, because you'd just turn everything white. About 1/4 power is as high as you normally need, even when you're bouncing it off of something. Therefore, HSS at 100% power is still usually bright enough.
However, one important use of flash is to balance out the sun, or to illuminate your subject the way you want to despite the brightness of sun. In this case, you need the flash to be very bright, and HSS just gets crushed on a small camera flash. Realistically, on battery powered units, you're looking at 10-pound strobes to really "overpower" the sun, especially if you want to use high speed sync.
In addition, high speed sync uses a ton of battery power, meaning longer refresh between shots, and fewer flashes. Plus, you're running it at 100% most of the time, meaning the flash will work for even fewer shots.
When you look at outdoor fashion and celebrity photography, you'll see big strobes firing off at 10 frames a second as the cameras click-click-click away, because "the shot" can happen in a fraction of a second -- and so your flash/strobe needs to keep up.
With a global shutter, the dream is, even outside, you can use a strobe at 1/3200 or whatever shutter speed you want, and either have a more powerful or longer lasting/faster refreshing strobe. And importantly, it means that photographers will need to lug around less/smaller gear to do on-location shoots. For example, if you're trying to do portraits at beach, you might be carrying stuff in a bag instead of a big case.
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