Set the camera’s exposure settings for the background and fine tune the flash to properly expose the people.

Your client wants a photo booth but no background

Maybe you’re on a gorgeous rooftop with a view of the Chrysler Building,  maybe you’ve got the Grand Canyon or the Braves’ new ball park in the background. You’ve got to find a way to adjust exposure so that background looks good and your guests in the booth are also properly exposed.

First, you’ve got to set the exposure of your camera so the background is perfectly exposed. It’s a long way from flash to background, so your flash will have absolutely no effect upon the background. But your flash is going to provide all the lighting on your guests.

How do you strike a balance?

1. You have to set your camera’s f-stop, shutter speed and ISO so the background is perfectly exposed.
2. Then you must adjust your flash unit (speedlight, monolight, whatever you’re using) so the people in the picture are properly exposed too.

The Rule of f 16 – there’s an old guide to exposure dating back to the film days. In bright sunshine, your basic exposure will be a shutter speed equal to your film speed (ISO). So with Kodacolor 100, in bright light you’d get a pretty good result with a shutter speed of 1/100^th of a second and f16. Or a 200^th at f11 or a 400^th at f8.

Too high a shutter speed and the flash can’t illuminate the entire photo at once.

You’re limited to the top shutter speed at which you can use flash without getting a shadow bar from the shutter (see previous posting). But in general it’s not safe to shoot much faster than 1/200^th with a DSLR camera. Canon Powershots can shoot faster and of course webcams can’t be used with a flash anyway.

In the photo with the dark area, only part of the sensor was exposed to the flash. So a part of the foreground is dark. The background is properly exposed because it was exposed by the ambient light.

So we’re going to set the shutter speed to its highest safe-sync setting.

We’ll choose a low ISO – 50 or 100.

We’ll try different apertures/lens openings/f stops until the background looks “right”. In bright sunlight you’ll probably end up around f8 to f11.

Now how will we make the subjects – the people – properly exposed?

By changing the amount of brightness coming from the flash unit. You’ll need a fairly power light source such as an Alien Bee and you’ll have to be fairly close to the subjects. Now is not the time to use a thin umbrella, too much light will get lost.

Just adjust the power percentage until your subjects’ faces look good. With a little practice it becomes easy. You’ll also find that moving the flash closer to the subjects makes them look brighter, moving the flash away makes them look darker.

You’ve got an additional concern when using a natural background – it’s going to get lighter and darker as the day goes by. We’ve already set ISO and shutter speed and lens opening for bright sunshine. As it gets darker – clouds block the sun or the sun is setting – we want to adjust the brightness of the background without affecting the guests.

It’s simple – just keep lowering the shutter speed.  That will make the background brighter.

If it starts getting really dark and you don’t want a longer shutter speed – perhaps you’re already down to 1/60^th – you can start opening up the lens a bit or bumping up the ISO. If you do that you’ll want to scale back on the light intensity.