Flash sync speed - does this make sense?

[Vtec44]

I tested the commander mode on my D7000 to activate my SB800 wirelessly. If the camera is set to activate the flash in TTL mode, max synch speed is 1/320. However, if I wirelessly activate my SB800 in Manual mode, I can go all the way up to 1/8000 without shutter shadow. I tested it with my SB600 with the same result.

 

[OrionsByte]

At shutter speeds above your camera's sync speed, it will use what Nikon calls "Auto FP Sync" (Canon calls it something else). Basically it forces the flash to stay on for the entire 1/320th of a second between the first and second curtains, so that even though each part of the sensor is only being exposed for 1/8000th or whatever you set it to, the flash is on the whole time - thus no curtain shadow. It will put out less light than a normal flash burst but it will drain your batteries faster because it's staying on longer as well. Take a shot at 1/320th and again at 1/400 and you'll see what I mean.

Edit to add: the built-in flash is incapable of Auto FP mode, but your SB-600 and SB-800 can both use it either on-camera or via the CLS system.

 

[lenejetlee]

yea it really make sense........

 

[Big Mike]

Brain nailed it. You can use a faster shutter speed with flash...using the feature called Auto FP (Canon calls is High Speed Sync (HSS)).

 

[D-B-J]

Brain nailed it. You can use a faster shutter speed with flash...using the feature called Auto FP (Canon calls is High Speed Sync (HSS)).

Yup. Auto FP is a great feature, especially when shooting things you need to stop dead in their tracks. I use this for water drop photography. And also, when shooting outdoors with a flash, and you want to underexpose the background, but 1/250th isn't enough, use auto FP and now you can go up to 1/400th, to really get separation (say with a portrait). So yes, it makes sense.

 

[KmH]

The flash unit doesn't stay on, it flashes multiple times during the single exposure.

The faster the shutter speed, the more times it flashes during the exposure.

At shutter speeds faster than the x-sync speed the shutter is never fully open, and is instead a slit. The height of the slit gets smaller as shutter speed is increased. The height of the slit determines how many times the flash has to fire during the exposure.

 

[Big Mike]

Also, when using Auto FP (or HSS), your working distance is severely limited. So while it does work, it still takes a very powerful flash to light up a subject that is say, 10 feet away.

 

[D-B-J]

Nikon CLS Practical Guide: 10. Auto FP High Speed Sync Explained

A worthwhile read

 

[Vtec44]

Interesting. I know about FP highspeed sync but didn't realize it can sync at 1/8000. This just opened a whole new door of creativity for me

 

[OrionsByte]

Just remember that when using FP sync, you no longer have separate exposure controls for ambient and flash. At speeds below the shutter sync speed, the flash can put out up to its full power in less than half the speed of the shutter, but in FP sync it has to reduce power in order to light the scene for a full 1/320th of a second. This means that the flash output is no longer "immune" to shutter speed changes the way it is in "normal" flash photography.

About the only thing you can do, as mentioned above, is get your flash really close to your subject.

Do some tests at various shutter speeds to get the hang of it before you run out and try it on something that matters.