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Rear Curtain Flash Sync Explained
Rear Curtain Flash Sync Explained

Dave Fiala - October 9, 2020

Here I go again!

I thought I would share some information and tips about another flash mode. This time I want to tell you about Rear Curtain, also known as 2nd Curtain Sync.

So for starters here is what it is and how it works.

We talk about our camera having a shutter curtain that opens and closes to control how long of an exposure we are going to make. Your DSLR has TWO curtains. The front, or 1st curtain and rear, or 2nd curtain. The reason there are two different names for the two curtains is for the most part because camera manufacturers did not get together and agree on one name to give it.

When we press the shutter button we think of the shutter(as one part) opening and closing. The way it works is that when we press the shutter button the 1st or front shutter curtain opens exposing the sensor or film to light. At the end of the exposure, the 2nd or rear curtain moves across the film or sensor plane closing to end the exposure. If we are photographing a car going down the street at night if we are in front curtain sync and we are taking, for example, a one-second exposure. When we press the shutter the first curtain opens and the flash fires. The shutter remains open for the one second and then the rear curtain closes halting the exposure. In rear curtain sync, the front curtain opens. At the end of the one-second, the flash fires, and the rear curtain closes. Thus, with front curtain sync, the flash fires at the beginning of the exposure while in rear curtain sync the flash fires at the end of the exposure.

Here are examples of photos taken with front curtain and rear curtain sync.

Front Curtain Sync

The picture of the car shot in the default or front curtain sync shows the streaks from the headlights and taillights coursing through the image of the car. It does not make sense. The solution to this problem is using rear curtain sync so that the streaks from the headlights and taillights follow behind the car.

Rear Curtain Sync

When the photo is made firing the flash in rear curtain sync the result is an image that accurately depicts the direction that the car is traveling.

Give rear curtain sync a try. It can also be fun and useful when shooting people in action. Do some experimenting with it and see what you can come up with once your rear curtain sync creativity starts to flourish. You will never know what fantastic shots you might get until you give it whirl.