Cook the Ambient
Last night I receive a call from my good friend Jenn and she says she needs a shot of her bike at night at an easily definable location. No problem, got time tonight? Sure.
Camera, 24-70mm and 10-22mm, Pocket Wizards, two flash units and my trusty voice activated light stand (Michelle) was over because we were going to go to the local camera club. On the way to the location I piece together the shot I want in my mind, what are my main challenges? Well it’s going to be dark so I need a flashlight to correctly focus on the subject. I’ll need to get low and possibly on the ground. I’ll also need to cook the ambient to balance flash with the lights in the background.
Well, at least I could do the last one. I forgot my trusty flashlight and I was still in my work clothes from earlier in the day. Thankfully we had cell phones that were bright enough to focus on and well, I might have ruined a set of pants laying on the asphalt.
So what is cooking the ambient? Also known as dragging the shutter, cooking the ambient is a technique of allowing the ambient light in your scene catch up with the exposure of your flash. If I would have taken the shot and only exposed for my flash while using the highest sync speed my camera allows I would have taken a shot like this:
Minimal Ambient
Boring. What’s that in the background, a UFO? Here we have a subject and no sense of location. Sure, the bike is lit but how do we get the background to lighten up? We cook the ambient which means that we’re going to pick an aperture and ISO to correctly expose for the flash to light our subject, however we’re going to hold open (or drag) the shutter to let the ambient light expose the film.
But wait, if the flash-lit subject is properly exposed at 1/250th of a second at f/4 and an ISO of 200 won’t a photo at 1/2 of a second at f/4 and ISO of 200 be blown out? No, because a flash is momentary. If the flash lasted the whole 1/2 of a second, sure. But it doesn’t. Let’s step through the process.
You set the camera at one half of a second, f/4 and ISO 200. How did we come up with a half of a second? First I expose for the flash like the image above. I figure out where I need to be in terms of aperture and ISO. We switch the camera over to aperture priority and set the aperture to the same value as it was for the flash and see what it tells us we need to set the shutter speed to in order to capture the ambient light with the aperture we’ve chosen. Next we go to manual and set f/4 and ISO 200. That will get our flash-lit subject where we need it. Now we drop the shutter speed way down to 1/2 of a second.
More Ambient
We click the button and the camera opens the shutter, at the same time the flash fires and really only lasts less than 1/10,000th of a second. All depends on power and the flash unit. So at 1/10,000th of a second into the frame the flash is done, it has frozen our subject into the frame. Now we have the rest of what is left of the 1/2 of a second exposure.. What happens? Everything lit by ambient light is much darker than the flash but cumulatively adds up and keeps cooking on the frame. Of course be sure to use a tripod, or not. Hand-holding a camera at 1/2 of a second will certainly result in some shake, but you may like that.. I did.
To the right is the frame at a much slower shutter speed. Not the best in the series (see how the ambient light on the bike starts to be a problem?) but the good ones have Jenn in them. This is just for something I can show everyone. You get the idea..
And after that how about getting creative while you’ve still got that shutter open, here is the exposure that I zoomed in with the lens after the flash was popped.
'Zoomed' Ambient
What do you need to worry about? Make sure that your ambient on your subject does not cook on the frame too much to muddy your flashed exposure and if you’re going to do any twisting or zooming effects on the frame, make sure your ambient does not cross over your subject. Best results happen when you pop a flash on your subject and then for the rest of the frame that subject is dark. Any light that comes across that spot on the frame will contaminate the effect. Which may or may not be what you want.
This was fun and challenging. So glad i could be the trusty voice activated light stand. LOL
But the shots did turn out good – just have some better ideas for next time. :)
Nice pics! I could actually tell from the first one where you were, but then again, I like bridges :)
that is a good idea. A flash light to get a focus lock. I have NO idea why I never thought to stick one in my camera bag. duh.