The human eye does a great job of compensating for the dark and light areas in a high contrast scene. When these light or dark areas reach the extremes, we need to reach for a flashlight or dark glasses, but for the average high contrast scene, our eyes do a great job of automatically compensating. Today’s digital cameras are getting close to matching this dynamic range of adjustment/compensation, but they still have a long way to go. For example the human eye sees at about 11 f-stops, while digital camera sensors see only about 6 f-stops.
One technique to achieve additional dynamic range in our digital images is to capture a series of photographs at differing exposure levels (exposure bracketing), then combine them into one final High Dynamic Range (HDR) image during post processing. This “combined” image would then contain the best characteristics of the series of images.
HDR photography tips
When capturing images for HDR processing it’s important to remember the following guidelines:
- Always use Aperture Priority when bracketing (because you don’t want the DOF to vary).
- Use a small aperture, because virtually everything should be in focus. Of course if you are shooting portraits and you want the background blurred, you would shoot with a larger aperture.
- Typically use a wide-angle lens (the benefit of HDR is being able to take what your eyes see, and replicate that effect in a photo with a very wide dynamic contrast range).
- Use a tripod and shutter release cable.
- Lock the mirror and focus.
- Shoot with a “bow & arrow,” as opposed to a “shotgun”—be selective of the composition and camera settings.
- Don’t always bracket around 0EV. Sometime the shot calls for starting the bracketing above or below 0EV. Look for the trouble spot in your image. For example, if the trouble spot is the shadows under a bridge, and not the highlights in the sky, shoot the majority of your bracketed shots in the higher end (more plus bracketed shots), and less on the lower end.
- Use the lowest possible ISO. Any noise you introduce to your bracketed shots will be amplified during the HDR process.
- As contrast increases, so does the bracketing range (more contrast = more bracketed shots). For example, a photo with more highlights requires more minus bracketing, and one with more shadows requires more plus bracketing shots.
How many bracketed shots?
How many bracketed shots should you shoot? Some say 3 to 5, while others say 7 to 9. The answer really relies on the contrast of the scene you are trying to capture.
Using the sun’s position to determine how may bracketing shots to take.
- Toward the sun = High contrast, so capture more bracketed shots
- 90 degrees to the sun = Moderate contrast, so capture fewer shots
- Back to the sun = Low contrast, so capture even fewer shots
In this tutorial I’m using a series of images that were taken without a tripod (yes I know, I’m already straying from my guidelines). Because the images were taken in fast succession using the burst mode function of my Nikon D700 they’re still usable—I will however have to align them before processing for HDR.