We've had several "thematic" assignments recently, so now I think it's time for a more technically challenging assignment. The assignment for the week of 19-25 January 2009 is "Backlit." Simply put, the primary light source for the image should be coming from
behind your subject. This often results in a much more dramatic image than can be accomplished with front lighting; however it is much more challenging to compose a successful image using backlighting. This is because backlighting typically results in very high contrast scenes. These scenes are hard for your meter to expose properly, and it is often necessary for the photographer to intervene and manually set the exposure to get the results they want. In many cases, the dynamic range of the scene (the range between the darkest and lightest areas in the scene) is so extreme that some areas of the image will be underexposed, while other areas will be "blown out" (exposed to the maximum possible brightness). The photographer will need to make a conscious decision on how to expose the image to place the light values according to their "creative vision."
In the backlit columbine image below, I wanted to capture the "luminescence" of the backlit columbine petals. This meant I needed to set the exposure so that the petals were a little brighter than mid-tone, but it also meant that I would be "blowing out" (over-exposing) the white petals. I chose to minimize the "blown out" areas in the scene by adjusting the position of the camera so that most of the "blown out" white petals were photographed from the side, thereby minimizing the distraction of blown out highlights. I consciously placed the shadowed areas in the background to help isolate the subject and emphasize the dramatic lighting in this scene.
Backlit Columbine
There are two ways to control the exposure to get the results you want. The first (most precise method) is to use spot metering and manual exposure. Spot meter on the important areas of the scene, consciously decide how bright or dark you want these areas compared to "mid-tone" and set the manual exposure accordingly. In the case of the columbine, I would have spot metered on the brightest areas of the
blue petals and set my exposure so that this "spot" was exposed at +1 stop above mid-tone. (+1 on the camera's exposure scale.)
The second method is more "trial and error" but is often the method many of us default to, mainly because we don't take the time to think everything through before we take the shot.
For the columbine shot above, my camera was already set on aperture priority and matrix metering, so I took a "test" shot, examined it on the LCD, decided I needed about -1/3 stop exposure compensation, and took the shot again to get the results you see in the image above. If my exposures had been way off during the first test shot, I would have adjusted my technique and used the spot metering and manual exposure technique described above. As it was, the balance of light and dark portions of the scene was such that the matrix metering "got lucky" and selected an (almost) appropriate exposure that could easily be tweaked with a little negative exposure compensation.
The assignment for the week of 19-25 January 2009 is "Backlit." You should compose your image so that your primary light source is coming from behind your subject and provides dramatic emphasis to the subject. Please upload your images to the "Backlit" album in the Weekly Assignments category of the Gallery no later than midnight, Mountain Time (GMT -07:00) on Sunday, 25 January 2009. I look forward to seeing some dramatic and creative images.
Keith
