Day 54: Why is There a Black Bar at the Bottom of my Flash Images?

It was 2012 and I was sitting in yet another lighting workshop trying to wrap my mind around all the complex crap flash brought to my photography table. “Can’t I just write that I’m a natural light photographer on my website and opt out of this?” Nope. I wanted to be a wedding photographer and with that, came shooting in all kinds of different lighting scenarios. So, feet planted, I learned about rear curtain sync.

You learn real quick that your shutter opens, the photo “records” and the shutter closes. End of story.

Well, I’m here to tell you, the shutter is actually made up of two curtains. A front curtain and a rear curtain. The front curtain opens to expose light to your camera sensor and then quickly following, the rear curtain closes and the whole thing resets for your next photo. We’re thinking curtains like in a theater, right? Ok good.

The thing to keep in mind is, when using flash, the flash doesn’t fire until that front curtain is completely open.

Repeat: The flash will not fire until that front curtain is completely open.

Now in the case of bright lighting, your shutter might be set to something high like 1/1000 of a second. In this case, your rear curtain will start to close before the front curtain is fully open.

So when using flash, knowing that the flash won’t fire until the front one is completely open, this means that your flash will fire while the rear curtain is closing. This will result in a black bar on the bottom of your image. The faster the shutter, the bigger the bar, so to give you an idea, check out the image below:

All that to say, when shooting flash, you should not have your shutter faster than 1/200th of a second.

Super easy, super simple, but that’s one question I get all the time from people learning flash. That’s also a story I hear told all the time from people who learned flash in the past and had this “What the heck is going on??” moment pop up at an inconvenient time in their photography career.

For most of us, the rule of “Don’t go below 1/200 of a second” is enough. Black bar problem solved. For people who want to go a step beyond, you can set your camera to close at the end of your exposure instead of the beginning. This is called “Rear curtain sync.” For example, let’s say you’re shooting a 2 second exposure on a tripod, changing WHEN the flash fires can change the shape or positioning of any trailing lights. If you’re interested in learning more about this, Mark Wallace (the teacher from the above mentioned workshop) has a great video outlining this very topic. Check it out right here:

Friends, that was day 54. Tomorrow we will continue this lighting train with bouncing a flash indoors. See you tomorrow!