Determining Proper Exposure For Specular Reflections
While sitting at the marina on a sunny day watching the sun nearing the horizon, I noticed the water was full of dancing reflections. What a perfect opportunity to demonstrate how to properly expose a scene with a high degree of specular reflections, or highlights. The above image is a culmination of five different exposures showing the results of using exposure compensation (EC) to over-ride the in-cameras metering of the scene to make the correct exposure. I only wish that in the time it took me to complete my exposures, a boat or kayaker would have gone by to show additional positive effects of exposure compensation.
I used Aperture Priority (AV) and evaluate metering mode for each of the six images.
Image 1. Cameras metered exposure.
Image 2. Minus 1/3 stop from cameras metered exposure.
Image 3. Cameras metered exposure, but with the addition of a Circular Polarizer.
Image 4. Plus 1 stop from cameras metered exposure.
Image 5. Plus 1 1/3 stops from cameras metered exposure.
Image 6. Plus 1 2/3 stops from cameras metered exposure.
Image 6 is the actual scene I saw through the viewfinder. Therefore, we could say that the in-camera meter reduced the amount of light by almost four times to meter the scene.
Since we all know that our digital camera meter measures reflective light, which is the intensity of brightness that is being reflected by an object created by the incidence of light, or the light source. In addition, we know todays in-camera metering is designed to evaluate the brightness of light reflected from an object of middle gray tone from 10% to 18%. We need to know what happens to the cameras meter when it runs into a scene with specular reflections or varying degrees of highlights. Its simple, it under-exposes the scene.
Another simple example would be to photograph a car in the bright sunlight. The first item you notice is the sunbursts (specular reflections) being reflected by the windshield and the brightly chrome bumper. If you let the camera do its normal metering on this bright scene, those sunbursts of true white (no color) will turn a dull grayish and the overall contrast of your image will become flat. By adding exposure compensation you retain those colorless highlights and the image will have the impact of the scene that originally struck your eye.
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