Photo Technical

Make lighting judgments in a flash – A11

Last time the topic was composition and there will be more on that at future ports of call.  Consider whatever is discussed, it is all to help you creatively take better pictures.  Now let’s come back to that primary subject of controlling light, this time using your cameras’ built in flash.

The other weekend I was staring out at the inter-coastal waterway.  It was a typical pleasant sunny day in South Florida.  A big yacht came slowly floating by.  A man was on the stern deck, holding his camera to take a photograph of a home on shore a couple of hundred feet distance away.  Suddenly the flash went off and I new he had taken his shot.

The question is why did he have his flash on?  This photograph, taken from the yacht of this relatively distant home, derives no lighting benefit from the flash.  There is only the negative result of depleting the camera battery power that much sooner.  I bet he didn’t bring a charger (if he had time to recharge) or an extra battery.

It’s also the same question I ask when I see one flash after another go off at a night football game by fans taking pictures from the bleachers.  In this case, not only are the camera batteries being depleted faster, using their flashes are adding detrimental elements to the photos being taken.

The flash will only light up the back of heads of spectators sitting immediately in front of you; it will have no effect on the playing field.  Creatively this will make such a photograph less appealing.  The people sitting in the one or two rows ahead are better left as silhouettes.  Light from the camera flash exposing them only makes them a compositional distraction to what is really the focus that is the players on the field.  The light given off by the camera flash does not carry past two rows, so the players are exposed only by the bright stadium lights.

The point is that the built in flash on compact or point and shoot cameras is not very powerful.  In technical jargon the power of a flash is given by its Guide Number (GN), and for these cameras it is very low, meaning weak.  Light output generated by a flash is also subject to a fall off related to the inverse square law.

This means for every doubling of the distance between the subject being photographed and the camera, the light from your camera’s flash that reaches the subject  is diminished or reduced by 4 times.

If at 1 foot you have full use of the light output from the flash, at 2 feet you only have 1/4 of the light, at 4 feet only 1/16, at 8 feet 1/32 of the light reaches the subject, and so forth.  You get the picture; at 10 feet the output light from a flash is already tremendously reduced.  The flash has to throw out all its power to light anything at 10 feet.  Any subject further away may likely be under exposed (dark).  Even the most powerful independent flash units you can buy have their limitations.

Trito Flash Fill01bw

Flash fill saved this photo of James, Sandy, and Bill, taken in less than ideal light

Nevertheless, the camera flash can come in very handy.  For instance, I use it often for flash fill.  Every compact camera has a flash, and flash fill means using it (when it is daylight and you might think you don’t need it) to fill in shadows with light.  Check out the sample photo courtesy of The Triton Party Animals (from left to right) James, Sandy, and Bill.  The flash fill photo of them published here looks fine, although their distance was almost out of reach for the flash.

If I had not used the flash there would have been one of two other results.  Either 1] we would have had the beautiful sunset sky, but their faces would have been completely dark and unrecognizable, or 2] it could have exposed their faces well, but with a totally undefined washed out blinding white sky background showing no cloud definition.  Either way it will not be as nice as a flash fill photograph.

Your camera has three settings for using the flash – auto flash, flash, and off.   To use flash fill you need to set it for “flash.”  The how and why will have to wait until next time.

For now, keep in mind that with flash fill you can capture the best of both worlds, clearly see the foreground subject(s), while also capturing the beautiful evening sky, clouds, and subdued backdrop.  Just remember it will not work for you if the subject is beyond 10 to 15 feet away.  Don’t expect miracles; if any subject exceeds this distance remember you can turn the flash off and save your power for a better occasion.  In the meantime…. permission to come ashore!