Brit­tany — © Copy­right 2012 by William Beem

How to Deal with Dis­tract­ing Backgrounds

I used light falloff to deal with the dis­tract­ing back­ground of a pool hall in the photo above. A friend who was with me decided to deal with the prob­lem using a shal­low depth of field. We both shot this model in a sim­i­lar pose, but our images were very different.

The idea was to go to a pool hall and shoot some pinup-​style and period piece pho­tos. Unfor­tu­nately, it was a mod­ern place in a strip mall. That meant the envi­ron­ment didn’t really match the con­cept. OK, so some­times you don’t get every­thing handed to you on a plat­ter. We tried some shots with the envi­ron­ment and a few worked. Most didn’t. Try­ing to sal­vage what was left of the shoot­ing oppor­tu­nity, my friend and I decided to go for iso­la­tion shots. He used his 85mm f/1.4 lens and I used my flash.

Light Falloff vs. Shal­low Depth of Field

The pool hall had plenty of light from a wall of floor-​to-​ceiling glass pan­els. My friend put that to use with his lens using an aper­ture of f/1.4. That let in plenty of light, but also gave a pleas­ing bokex to the back­ground. For me, it still didn’t work for my taste. Although the back­ground was out of focus, I thought the back­ground was still dis­tract­ing. Instead of a solid color, there were just dif­fer­ent blurry col­ors behind her.

Using light falloff, I knew I could basi­cally elim­i­nate all of the light from the back­ground and my model would appear on a black back­ground. Choos­ing between that or the dis­tract­ing back­ground, I decided to go with the light falloff technique.

Under­stand­ing Light Falloff

The con­cept is pretty sim­ple, though it’s often described in a con­fus­ing man­ner. Peo­ple bring up the Inverse Square Law when dis­cussing light falloff. Although that’s the cor­rect prin­ci­ple at work, you really only need to under­stand one sim­ple concept.

Every time you dou­ble the dis­tance your light has to travel, it loses 2 stops (75%) of its power.

That state­ment sums up what you need to know about the Inverse Square Law. Now you just need to know how it applies to you as a pho­tog­ra­pher. The answer depends upon some key expo­sure variables.

Remem­ber, flash dura­tion is much shorter than your expo­sure. Most cam­eras can only sync up to their flash at ¹⁄₂₀₀^th of a sec­ond. The flash dura­tion is much shorter, though — over ¹⁄₁₀₀₀^th of a sec­ond. That means your shut­ter speed isn’t the decid­ing fac­tor in con­trol­ling light falloff from a flash. I set my shut­ter speed at ¹⁄₁₂₅^th for this image. Rea­son­ably quick, but still below the sync speed require­ment for my flash.

Your ISO con­trols your camera’s sen­si­tiv­ity to light. The lower you can set it, the less its affected by light hit­ting the sen­sor. One of the first places to start with your ISO is at its low­est set­ting because you’re try­ing to elim­i­nate back­ground light. I shot this photo at ISO 200, which is the native set­ting for my Nikon D700.

The next part of the expo­sure tri­an­gle would be aper­ture, but deal­ing with flash intro­duces two new vari­ables into the expo­sure equa­tion. Your flash power is one, and the dis­tance from your flash to your sub­ject is another. I kept the flash on a light stand, so the dis­tance from flash to sub­ject remained constant.

That leaves you with your aper­ture and flash power to adjust light falloff. Before intro­duc­ing the flash, I adjusted my aper­ture to f/​9. That, along with the ISO and shut­ter speed set­tings I men­tioned above, is what it took to elim­i­nate the ambi­ent light from my expo­sure. If I opened my aper­ture from this point, I would start to let ambi­ent light creep back into the shot. That would also mean bring­ing back the dis­tract­ing background.

Now I could start intro­duc­ing the flash to the expo­sure. I needed at least enough power to evenly light my sub­ject with the expo­sure vari­ables I set on my cam­era. How­ever, the dis­tance between my flash and the sub­ject mat­tered in two other ways. The first is one we dis­cussed with light falloff. The closer I could get my light to my sub­ject, the faster the light would falloff. The other is how hard or soft the light falls on my sub­ject. As I bring it closer, the shad­ows are much softer.

Let’s take a look at light falloff in more detail. Remem­ber, every time I dou­ble the dis­tance the light has to travel, I lose 75% of its bright­ness, or two stops. That dis­tance can be very small. If my sub­ject is an inch away from the light, then mov­ing the light back two inches means I’ve lost 75% of the bright­ness out­put by the flash. The next move to dou­ble the dis­tance is four inches, then 8 inches, 16 inches, then 32 inches. Each time we dou­ble the dis­tance from flash to sub­ject, we get a larger zone until light falloff.

If I want rapid light falloff, then my flash much be very close to my sub­ject. Of course, that depends upon the power and other expo­sure vari­ables remain­ing con­sis­tent. Another way to achieve the same result is to vary my flash power or vary my aper­ture. Which is more con­ve­nient for you as a pho­tog­ra­pher? The aper­ture, of course, since it’s right there on your cam­era to control.

With all other expo­sure vari­ables remain­ing con­sis­tent, your aper­ture deter­mines how much light enters your sen­sor. Using a smaller aper­ture lets in less light. The light we elim­i­nate is less bright than the light that enters. Every time you reduce your aper­ture, you con­trol light falloff by only allow­ing the more pow­er­ful, brighter light to enter your cam­era. If you look at the model above, you can see the light fad­ing is it trav­els from one side to the other. Even­tu­ally, we don’t see any­thing else because we’ve con­fig­ured out expo­sure to ignore any­thing below a given power of brightness.

You need to make sure that your flash has enough power to gen­er­ate the level of bright­ness you need. My Nikon SB-​900 was scream­ing in pain dur­ing this part of the photoshoot.

Using light falloff is a mat­ter of mea­sur­ing and con­trol­ling your light. If you have a light meter, you can do it very quickly and effi­ciently. How­ever, it’s still quite pos­si­ble with­out using a meter. Take a few shots to mea­sure the ambi­ent light and elim­i­nate it from your cam­era expo­sure vari­ables. As you add light from your flash, you can con­trol how far it trav­els by adjust­ing its power and dis­tance, and by adjust­ing your aperture.