Professional Photogaphy Lighting Depth

I have recently been thinking of lighting depth for use in photographing anything from a group of 40 to a shot of a toddler. When shooting an older child, adult, or small group you can get away with just placing the light and exposing. However when shooting a toddler, the risk is the little one will move closer and farther from the light as they squirm and do anything they can to not cooperate. When shooting a large group the issue becomes getting the people in the front and the back exposed the same.

Lighting depth works just like lens apertures, using the inverse square law. Because we are already used to aperture numbers (2,2.8,4,5.6,8,11,16), we can apply the same numbers to our distance calculation. For example. If our light is 4 feet away from the subject and our background is 8 feet away from the light, the background will be 2 stops darker. This is the same as the brightness difference between f4 and f8. If the background was 5.6 feet away it would only be 1 stop darker. Knowing this you realize you can do a bit of calculation in your head.

Something else to consider. Just to point out the relationship here, you can make your background darker by moving the light closer to the subject or by moving your subject closer to the light. If you move the light closer to the subject, it will also get closer to the background, but the background will actually get darker when you've properly exposed the subject.

This can be a bit to think about, so I will leave this here and follow up with my 2D Lighting depth calculator next time. I am going to try to make this available as a download for you to use.