Sunday, June 12, 2011

Exposing Multiple Image Planes

Behind Every Successful Foreground There Is A Background*: I'm going off topic for this posting to emphasize a point made in my last entry. In it I suggested that proper exposure is based on two image planes: the background and the main subject. In this image there are actually three image planes, each one requiring its own exposure setting. Let's look at each of the three images, and see how proper exposure was determined. Incidentally, I won't go into exact settings, since yours will probably be different from mine.
  • The LCD Panel: This would be set first because I could not control the intensity of the screen. Before making the first test exposure, I needed to consider the following: White Balance, ISO setting, Aperture, and Shutter Speed. I went ahead and set my camera to Flash white balance, since the majority of the image would be lit with flash. Luckily for me, the balance was close enough. Next, I went right up to the LCD and made a photograph at ISO 400, and settled on a shutter and aperture combination of 1/20 second at F5. Why these settings? The ISO setting was the lowest setting I could get away with. I was using a wide angle lens set to 14mm, and  felt confident that I could hold still enough to make a reasonably sharp photo of a static subject at that speed. The aperture setting was based on some quick exposure tests, and F5 was the winner.
  • The Background Display: The tent made it easy to illuminate the panels. I attached 2 Nikon SB-800 speedlights in Justin Clamps  to the steel supports of the tent. The flashes were oriented so the heads would bounce the light off the ceiling of  the tent and the CLS (Nikon's Creative Lighting System) sensors faced the  camera. The light, forced to go the extra distance from the flash tube to the ceiling and back to the panels helped to even out  the top-to-bottom illumination. Since the light was coming from above and essentially perpendicular to the lens axis, the was little chance for glare, but a little bit snuck here and there, but not enough to matter, in my opinion. These two lights were set to Group C, Channel 3, so they could be controlled separately from any other flashes. With the camera set to F5, the CLS made the necessary adjustments. I could have dialed the intensity up or down, or gone full manual if it was necessary. Luckily for me, the CLS got it right the first time, although it's a little hot in the far corner of the tent.
  • The Main Subjects: The two young ladies were positioned beside the LCD, and a third SB-800, attached to a monopod, was held aloft. No light modifiers were used. Once the subjects were in position, I moved my assistant from left to right to be sure that light would slide past the flat screen of the LCD, thus avoiding glare. Special attention was paid to insuring that both faces were reasonably well lit. This single SB-800 was set to Group A, Channel 3. If you look at the concrete, you can guess where the light was placed by looking at the direction of the shadows. I'll talk more about that in a future post.
Final Gripes: I have to admit, I have many photographs that could benefit from a "Mulligan", and this is no exception. Although nobody ever noticed it, you can see one tent-mounted SB-800 in the metal framework of the tent. The position was both fortunate and unfortunate: good because it easily saw the control pre-flashes from my camera, but bad because it's visible. Next time, I'll mount the flash higher up in the tent above the camera's line of sight and put my master SB-800 on an SC-28 or SC-29 cable and position the unit just below. This way the light will sneak up under the edge of the tent to find the sensor.

Why Channel 3? I set my flashes to Channel 3 when they are in the remote (slave) mode. The Nikon CLS allows for a maximum of 3 groups (A,B, and C) and 4 channels (1,2,3, and 4). This is true when using the SB-800, SU-800,  or SB-900 in the Commander Mode. The on-board commander of current production cameras (when the commander mode is available) has only 2 groups and 4 channels. But the D70, oldest and least capable of the built-in commanders, has only 1 channel and 1 group, 3A. Any remote flash used with the D70 must be so configured, and since I use my D70's frequently, I set all my flashes to Channel 3. It just makes it easier.

*I believe I am quoting Bob Schwalberg, a writer for the magazine Popular Photography in a time when cameras had more in common with watches than microcomputers.