Inverse Square Law

David Bergman explains how you can change your background by using the inverse square law.
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Transcript:

David Bergman:

I’m photographer David Bergman, and this is Two Minute Tips for AdoramaTV.

Today we’re talking about something that can sound really confusing, but has practical implications for all kinds of photography—the Inverse Square Law.

The Inverse Square Law tells you how quickly light falls off the further away it is from whatever you’re shooting. You might think that as you double the distance between your subject and the light source, that you would have half the light hitting them. But the truth is, you actually get a quarter of the light, and if you double the distance again, you get 1/16th of the light.

So it really has to do with the way that the photons of light spread out as they travel so they don’t all hit your subject equally. You can geek out over the science all you want, but I’d rather talk about it in practical terms.

Here’s the only thing you really need to know—the light falls off a lot faster if the light source is closer to your subject. This is really useful to know so you can control the ratio of light on your subject and the background.

Okay, so let’s put this into practice.

I’m here with my friend Tango and he’s standing in front of a white background. I’m only using one light and it’s pretty far away from him. You can see that the background is relatively bright. But now let’s move that light in, so it’s a lot closer to Tango. Of course it’s a lot brighter on him now, so we have to change our camera settings so that he’s properly exposed.

But now look at the background—it’s a lot darker.

So without moving my subject at all, I can create a completely different look from my photo.
This is also important to know when shooting a group shot of people, like a band, for example.
If everyone’s standing different distances from the light, but you want them to be lit pretty evenly, then you have to get your light further away from the entire group.

So listen—don’t stress out about the science behind the inverse square law, unless you’re into that kind of thing. But photography is really about using and controlling light, so use those scientific principles to make your pictures look exactly like you want them to.

Thanks for joining me today on AdoramaTV. Don’t forget to subscribe for more amazing videos.
Follow me on social media @DavidBergman and go to the Adorama Learning Center for lots of other great tips and tricks.