Know Your Sync

Pop quiz: What is your camera's maximum sync speed?

Much like the interstate highway at 3:00am, in some situations your max sync speed is not so much a law as a suggestion.

And by the same token, sometimes your instruction manual can lie: Your camera may not be able to truly hit its advertised sync speed at all.

As many of you may know, a camera that says it syncs at 1/250th might go a little better than that if you use a fast flash and a hard cord instead of a PW. And that little bit of non-sync strip at the bottom of your frame at a 1/320th might not be very noticeable.

Or it might actually help the frame, as in the not-quite-synced sunset shot at left. (More on that photo, here.)

And, speaking of that shot, if I wanted to I could easily have synced this shot at a 1/500th. Just turn the camera upside down and let the unsynced half of the frame fall on the sky. The sky needs no sync -- it is all ambient, right?

But On the Flipside …

We have talked about the over-the-speed-limit stuff before. Fun stuff. But camera engineers sometimes cut it close to hit that round shutter speed number. And sometimes they miss it.

Lemme ask all of you 5D MkII owners, what's your real sync speed? 1/200th, right? (The Devil was due something for all of the camera you got in that sub-$3k package. No 1/250th for you today.)

But it may be even worse than that. You may be getting a little banding at a 1/200th. And heaven help you if you are trying to fire a slow, "big light." Or even slave a quick, second speedlight off of your main speedlight.

Take this little setup, in Guanajuato, Mexico. I am being a VAL for Francoise, who is shooting at the bottom of the frame.

I tell her to just go to a 1/200th and get a good aperture for a rich sky, then we will add light in to bring Sara back up in a cool way. Even better, Francoise is on-camera filling -- so the shadows on Sara will not be black. Gonna look cool.

No problem, right?

Yeah, well, except that Francoise's 5D MkII is really a true 1/160th full sync. Which means that it will grab a partial sync of my slaved SB-800's light, but not all of it. So naturally, I keep walking up the power setting, to no effect. This is because the raised power setting is just making the flash duration longer.

The flash is firing, and partially synching. But most of the hi-power goodness is happening after the shutter closes. And Francoise, naturally, keeps getting more and more confused when Sara doesn't get any brighter.

Meanwhile, a few feet away, Peter Norby (who took both of these photos) is doing just fine. His camera -- also a 5D MkII -- is grabbing all of my slaved SB-800's flash pop. Same exact setup, same lighting gear and same conditions.

What Peter got was what I was expecting Francoise to get. But it was just not happening for her. And it wasn't until the situation happened again later in the day that I figured out the problem.

This time, Peter was the subject, in a similar lighting setup. We were three feet away with him, using a slaved, direct SB-800 at half power. I mean, I was starting to catch a whiff of burnt facial hair in the frame, if you get my drift.


Okay, actually just enough to see some flash, but probably 80% of the slaved pulse was not being synced by Francoise's 5D MkII at 1/200th. Which is supposedly it's sync speed. But not really.

Then it hit me: Francoise's camera might be a little … slow. We dropped to a 1/160th and shot another frame. This one looked like Peter was being lit by a small thermonuclear device. Which is exactly how my brain had been telling me all of the recent pops should have looked.

Test, Test, Test

How do you know if you have a slow camera? It's easy to test and find out.

Get in a darkish room. Put your flash on camera and set your shutter at your fastest true sync speed. Fire a full pop on a plain wall and adjust your aperture until you get a reasonable exposure. (It is important that you use a full pop, as that is the longest flash pulse your speedlight can produce. Crank the ISO down, and even still you may need to back up.) Now open up the shutter one third of a stop, i.e., from 1/250th to 1/200th, or 1/200th to 1/160th.

You should not see any difference. If you do -- a little brighter, maybe, or a little previously unnoticed banding disappeared in the slower shutter pop -- then your camera is not full synching at its advertised speed.

You can stress the situation a little, too, by using your on-camera flash at low power to slave an off-camera flash at high power. This will add a little sync delay in (very tiny amount) and show you your limitations in a multi-flash situation. Throw a PocketWizard up there, and maybe add in a slower "big light" and you may get some additional valuable info on the sync front.

My D3, for instance, will sync a full-power and extra slaved SB-800s, but will band a little at a 250th with a PW and a full-power AB800 or AB1600.

Next, Crank the Volume to 11

If you are dumb-syncing (PW, PC cord, etc.) crank your shutter up above your sync speed with your typical flash gear and repeat the test. This way, you can get familiar with how your camera bands a missed sync at a 1/320th and a 1/500th, for those times when you need a little extra ambient control.

As long as you know exactly what is not going to be lit by flash at those speeds, you can compose (and/or rotate your camera) to make it work.


New to Strobist? Start here | Or jump right to Lighting 101
Connect w/Strobist readers via: Words | Photos
Got a question? Hit me on Twitter: @Strobist
Save Money: Browse MPEX Weekly Strobist Deals