Sunday, April 13, 2014

Flash Overfill

The Rotary Club of Foster City presented the Adult School with a check for $1,500, a sizable gift considering the state of educational funding in California. Photos like this serve two purposes: in-house publications and external publicity.

For a lark, I decided to see how a camera like the Nikon Coolpix A would work as a "run and gun" camera for quick publicity shots as this. I decided to add a Nikon SB-900 speedlight with a Lumiquest 80/20 with the silver reflector in place. This effectively place my light source further from the lens axis, an important consideration when shooting indoors with the constant threat of "red eye".

I read recently that back in the 70's, some photographers had come up with a basic formula for using flash to fill in the subject's shadows. Put simply, it was suggested that you cut you "ambient" (metered, if you prefer) exposure by 1/2 of a stop, and set your flash to underexpose by 1/2 of a stop. Huh? 

Followers of Joe McNally once made a reference to a photo requiring a 2/3 under exposure in Aperture Priority mode, and 2/3 over exposure added to the speedlight exposure. Certainly McNally's advice is to be trusted. But here's the catch. The underexposures was accomplished using a plus or minus adjustment with the Exposure Compensation dial, which is global. This means that the ambient exposure and the speedlight exposure are reduced equally, and left uncorrected, will yield an image that is underexposed. The plus 2/3 stops on the speedlight is there to bring the flash lit portion of the image to "normal", while allowing the ambient to underexpose. Remember: exposure compensation affects both the ambient exposure value and the flash exposure value when using TTL and aperture priority together. This also presumes that the flash will be the primary light source on your subject.

Fill with flash is a different story. Here, the light used to restore detail in the shadows will also affect those areas receiving enough ambient light to make a proper exposure. In this photo of the wall outside of my office we can see, on the left, an image made without flash fill. On the right is the same exposure with the addition of the SB-900 set to 1/8 power based on a 9' flash to subject distance. It clearly returned detail to the shadow, but also noticeably lightened up the sunlit areas.
Another issue was the light source. As I mentioned, I used an SB-900 with a Lumiquest 80/20 and the silver reflector insert. This gave a somewhat harder light, but it was all I had. The 80/20 raises the light off axis, which provides some modeling. Unfortunately, it is still nearly on-axis lighting, so hot spots on the tips of everyone's nose inevitably result. I managed to improve the situation by using the clone tool in the darken mode. 

If you look back at the sample image, can see that there is a definite hot spot in the middle, something that normally wouldn't be noticed when photographing an actual person. But the nasal hot spots will still be there.

In this trial shot, you can see that the run and gun combination produce a reproducible photo with very little effort. Since both the flash and the ambient exposures were 1/2 of what they should have been, the filled shadows weren't too hot. A usable image, but certainly nothing worth adding to my portfolio.
One thing that you'll immediately notice is the "photo grey" sunglasses have magically transformed into dark, colorless disks. This is a pretty common occurrence, and was sure it would happen today. To eliminate this, I keep a pair of glasses frames without the lenses for those situations when I am photographing the boss in bright sunlight. This time I actually remembered to bring them. 

From this enlargement from the lead shot, you can clearly see the boss's eyes are clearly visible and suspiciously free from glare. Of course, he claims he couldn't see a thing. But obviously, it works! David Hobby likes to tell the story of a Chinese wedding photographer who carries a box containing 40 such pairs of lensless glasses whenever he shoots. When doing a group, he tells everybody to pocket their own glasses and chose a pair of frames from the box. As David said, that's a line that you want to be in the FRONT of!

When it came time to actually make the shot, the selected location put the sun at their backs and their faces lit only by the open sky. No longer a fill, the flash was now the key light, which I simply doubled the flash output to 1/4 power to give me a proper facial exposure. Granted, the lighting is a little flat, being so close to the axis, but the exposure was about where I expected it to be. It certainly isn't gorgeous softbox lighting, but as I said, it would do for a simple "run and gun" photograph.
Here's the shot once again. Granted, it doesn't have the smooth lighting that I get from my Zumbrella shoot-through umbrellas, or from a small softbox. But the rig was simple to carry and somewhat less clumsy, and more efficient, than my old favorite, the Gary Fong Cloud  Dome. But as I said, for running and gunning, it will do in a pinch.