I discovered this camera feature a long time ago with my Nikon D70 when I wanted to shoot a long exposure of a moving car at night. The built-in flash popped at the beginning of my 3 second exposure so the light trails went “through” the car. Not what I wanted. I needed that flash to go off at the end of my 3 second exposure so that the light trails would be behind the car. So I went through my manual and found this lovely feature called Rear Curtain. 🙂 After purchasing and reading The Moment It Clicks by one of my favorite photographers, Joe McNally, I discovered the logic behind rear curtain flash and that’s what I’ll try to convey to you in this lighting tutorial.
What is Rear Curtain Flash?
By default, your camera is set to front curtain, which means your flash fires at the beginning of the exposure, when the shutter opens. As mentioned above, rear curtain is getting your flash to fire at the end of your exposure, just before the shutter closes.
Ok, you’re probably saying: “that’s just fine and dandy Yanik, but what’s the difference whether the flash goes off at the beginning or the end of the exposure?” Well, you won’t see a difference at high shutter speeds but you will at slow shutter speeds. Remember what a flash does. It lights up your subject and “freezes” it in time. So if your flash goes off at the beginning of the exposure, you’ll freeze your subject and then the movement for the rest of the exposure will blur right over your “freeze” and it won’t look natural or sharp. If your flash goes off at the end of the exposure, the blur comes first and then…. BLAM! You freeze your subject right at the end making it sharp with all the blur “in background” of your frozen subject. Take a look at this example of a dancer. This is a 1 second exposure, hand held, in rear curtain mode and she was moving pretty fast. You can see in the 100% crop of her face how the sharpness was kept.
When to use Rear Curtain Flash?
All the time! No kidding. Really. My camera has it set to rear curtain since I read The Moment It Clicks. It was just that “aha!” moment. Think about it for a second. Let’s say your shooting at 1/250 sec. you’ll agree that whether your flash fires front or rear curtain, it won’t make any difference. But it will make a difference if you’re shooting at 1/15 sec. So why bother keeping it in front curtain mode?
Not convinced yet? Let’s say you’re at a wedding shooting indoors and it’s quite dark. You have your trusty Sb-800 or 580EX II on your camera, set to default front curtain, and you’re shooting in Aperture Priority (A) mode. What’s your slowest shutter speed? Go ahead check. You can check it with your built-in flash as well, it’ll be the same. So? Yup, you got it. You can’t go below 1/60 sec. in P or A mode. Why? The camera’s smart and doesn’t want you to make blury photos, that’s why. 🙂 What will happen at 1/60 sec. in a dark room? A properly exposed subject (by the flash) and a completely dark background loosing all the ambiance of the party.
If your camera is set to rear curtain, you can be in any mode (P, A, S /Tv and M) and the camera will adjust to the ambient light then fire the flash at the end of the exposure.
Here’s another example of rear curtain flash at a party this summer. I wanted to create a dynamic photo so I shook my camera during the 1 second exposure. As you can see, even while shaking my camera, the dancers came out pretty sharp! 🙂
To sum it all up: front curtain = BAD rear curtain = GOOD. 🙂 Ok, ok, that’s pushing it a bit, I know. I’ll say it this way:
– Front Curtain flash = having a sharp subject then smugged over it by movement blur
– Rear Curtain flash = having blurry movement then with a sharp subject over it
So keep your camera on rear curtain and you’ll thank me for it! 🙂
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