Tuesday, April 13, 2010

In Hindsight: Soft Light on Shaded Subject with Bright Background

This is the first of a series of entries where I examine some of the older pictures I took and analyze what I would have done differently.  My goal is to allow readers to learn from my mistakes.
Issue: Lighting
Situation: bright background; subject is in the shade.  Our hotel had a nice view and I wanted to capture the scenic background while illuminating the subjects with soft light.
How I did it then:
f8.0, 1/100, +0.7ev, iso 400, bounce to ceiling (camera rear left)
I believe my concern was to get sufficient depth of field to capture the background, so I think I used aperture priority and selected an aperture of f/8.  I probably bumped up the EV because my test shot was too dark.  I tried to get soft light by bouncing the on-camera flash to the ceiling.  Bouncing the flash in turn required bumping up the ISO a bit to 400.
Result:

From a lighting perspective the problem with the image is that the subjects are very underexposed.  The aperture of f/8 seems ok for the situation because most of the shot is in focus.  However, the shutter speed of 1/100 is not optimal.  The ambient could have been made darker without decreasing the flash power by setting the shutter speed at the sync speed (1/160 for the Pentax K100D).  Adjusting the EV was also not optimal because it would increase the exposure from both ambient as well as the flash.  It would have been better to adjust the flash exposure compensation to increase the flash exposure without increasing the ambient exposure.
How I would do it today:
The main issue with this scenario is the strong contrast between the background and the shaded area of our hotel room.
1. Due to the very wide range of contrast, I would need the most dynamic range I can squeeze out from my camera.  I would do this by using RAW not jpeg.
2. In terms of exposure mode, I would probably choose shutter priority or manual mode in order to select the maximum sync speed. At the sync speed, the flash has the maximum relative power over ambient.
3. Knowing I need to squeeze the most from the flash, I would set the flash on manual at full power instead of using TTL.  To maximize the flash power further, I would zoom the flash as much as possible.
4. To get soft light, I would have used an umbrella or softbox, which is more efficient than bouncing off the ceiling.  If that was not available, then bouncing would be an acceptable alternative.
5. Between aperture and ISO, I would prioritize aperture in order to get a reasonable depth of field.  I would choose the smallest aperture available that would get a reasonable exposure of the background.  To further maximize depth of field, I would focus on the hyperfocal distance.
6. Having set the shutter speed and aperture, I would choose the lowest ISO where I can get a reasonable exposure.
7. If necessary I would bring up the lighting on the subjects in post processing.
With the process above, the lighting would have looked kind of like this:

ISO 100, 1/200, f/4.5, flash with shoot through umbrella, triggered via CLS.
Other solutions:
It's also possible to take this shot with two exposures: one where the background is properly exposed and there is no subject, and one where the subjects are in the picture, properly exposed, blowing out the background.  With the blown background, it's easy in postprocessing to replace the background with the correctly exposed background.