How to take a picture of a group with flash so that everyone's face is lit evenly?

Question

A common situation in how I use my DSLR is to take a group picture at a badly lit location (think a table in a bar) with a flash. I have a flash that's pretty powerful even with a reflector and I have no issue with making everyone's face well lit, but the issue is that people standing closer to the camera are brighter than those in the back. My picture then come out looking something like this.

Is there a way to achieve a more even lighting spread without forcing people to stand equidistantly from the camera? I can use a flash bracket or a second flash on a tripod, but I'm not sure how to place them to achieve what I'm looking for.

Answer 1

Lighting a large group "evenly" with flash requires a powerful flash placed far enough away that the distance between closest and furthest subject is a small fraction of the distance from the flash to the closest subject. Consider the diagram Where A is the light source and B-E are subjects:

A----BCDEF

The distance A->B is 4. The distance from B->F is also 4. The inverse square law means that the amount of light from A->F is 1/4 the amount of light from A->B. Or two stops.

A----------BCDEF

Increase the distance from A->B to 10 and the falloff from B->F will be one stop. (10/14 is approximately square root of 1/2).

A----------------------------------------BCDEF

Back the light source way up where A->B is 40 and the falloff from B->F is about 1/4 stop. While ISO and aperture can help a little, mostly it is a matter of increasing power at the source or sources and/or decreasing the distance between closest and furthest subject. Even illumination is one reason big studio strobes exist. When recreating the sun, standing further back and shooting with a longer telephoto lens will increase depth of field at wide apertures.

Answer 2

If you use an off-camera flash for the group shot (and you should), the key concept will be light feathering : you should point the light directly to the person farthest from the flash, while the others (who are closer) will only get the edge of the beam.

Here's a whole strobist article, with this diagram:

This method helps a lot in order to get an even exposure, even with one single flash.

Answer 3

Use Bounce Flash

As other answers have noted, the problem is the inverse square law. The intensity of light drops off with the square of the distance between the source and subject.

By bouncing your flash off a nearby object, such as the ceiling, you can decrease the ratio between the squares of the distances. For example, say you have two subjects at 3 meters and 6 meters. The ratio of the squares is 9:36, or 1:4. So using direct flash, the more distant subject receives 1/4 as much illumination.

Measuring from your flash to a point on the ceiling, and then to each subject, their distances (just throwing out some numbers to illustrate) might be 7 meters and 10 meters, respectively. The ratio of the squares of those distances is only about 1:2 (49:100, to be exact). Thus, the illumination is much more even.

If your flash doesn't have a bounce head that can be tilted upward, you can direct the flash upward with a piece of white card.

Answer 4

Wedding photographers and sports photographers must solve this problem as part of their job. In addition, everyone in the shot must look good, have their eyes open, and their wardrobe closed.

The way to do this is by finding a camera POV that minimizes the depth of the subject to be within a workable lighting distance determined by the source guide number.

In the sample you provided, a better position would have been to move toward the left to reduce the distance to the furthest one of subjects.

Answer 5

Here's a handy tip that uses an application of the inverse square law.

TIP:
The f/ #s on the barrel of a lens can be used to judge the depth of light fall-off - without a calculator - due to the application of the inverse-square law.
From 2.8 to 4 feet, the light will fall off 1 stop.
From 4 to 5.6 feet, the light will fall off another stop
From 5.6 to 8 feet, the light will fall off another stop
From 8 feet to 11 feet, another stop,
and so on.

Using this TIP, you can see that putting a model about 6 feet from the source, gives the photographer a full 2-1/2 foot-deep zone of light that has less than a stop fall off. This is well within the lighting ratio for, and range of, flattering portrait light.
(This is an application of the Inverse-Square Law)

Suppose the subject was a piece of equipment that was 3 feet wide. Placing the subject 8 feet from the source ensures that from the closest point to the furthest point of the equipment is within one stop—well within the acceptable lighting ratios for product photography printed brochures.
(This is another example of the Inverse-Square Law)

Answer 6

There are a few ideas that are known. If your group is standing in multiple rows, then that's a problem when the rows are at different distances. Placing the flash high can help a little, for example a flash 45 degrees high lengthens the path to 1.414x longer, which extends the tolerance of +- 1/3 stop by 1.414x further. And of course curved rows more closely spaced helps.

If you use two direct lights on the row(s) of subject, one plan is from near the row ends, aimed at 45 degrees back to the center. Any two lights will overlap causing bright spots, but in this 45 degree path to center, both lights are falling off in the center, equalizing the overlap mixture. The amount one light is falling off is made up by the other light increasing (and the sum is the result).

This is good on single rows, however on multiple rows, two lights towards the ends makes different and terrible shadows of heads in one row onto the next rows heads (which cannot be seen until the final picture) so it's more common to put both flashes in the center above the camera, aimed out towards ends (lighting same view as what the lens sees). This eliminates the shadows, but equalizes less well, the ends are more dim, and you risk a strong center overlap.

Bounce flash is always an equalizer of distance (reasonable distances). If your group is seated at a long table at home, bounce flash is your best bet to equalize the light (and likely best lighting too). If a very long table, then another bounce flash about half way of the length for the rear half. But on a bar ceiling, bounce flash may not be possible/productive.

I think the Fong diffuser concept is counterproductive to preventing wall spill, because wall spill is its only purpose. There are many better lighting ideas, umbrellas for example. Diffusing has multiple rather different meanings. If it is a tiny light (like that tiny dome), all diffusion can do is scatter the light outward, away from the path to the subject, scattering light everywhere else, much more likely to reflect from the walls (although wall distance is always an issue of it making it back). The definition of a "soft" light is very different, specifically a large light (3 or 4 feet instead of 3 or 4 inches), large enough to merge the far paths back towards center, actually reaching the subject (from different directions to soften any shadows, each path filling the other paths shadows).

Answer 7

It's probably impossible. Even if you can have your subjects at the same distance to you, you can not control external factors, such as wall or clothes colors and reflectance. And you will undoubtedly end up with faces half-lit by different light source, even if your flash is powerful (generally red and green, far from a perfect mix...).

The best "portable" choice is probably to light as evenly as you can, using a mountable flash diffuser (like a Gary Fong Lightsphere). You can also try to use a flash on your camera and another one that you can put on a tripod, on a table or that you can hold by hand. Then you will have to find how to set up flashes power, not an easy feat if lightning is changing or if you often change places. And your customers won't probably like being made blind after your fifth test :)

More than 2 flashes will probably be hard to carry/setup, and you might be better off making a small photobooth.

Once you have a correct image, you might use post-processing to improve things, but in my opinion, it's very time-consuming, unless you only work on a few images.