HDR Photography: A Stop of Light and Automatic Exposure Bracketing
If you are shooting (or wanna shoot HDR) this is good news. The fine folks at SLR Lounge recently released a new 3 DVD set called Comprehensive Guide to HDR. Like any of their DVDs it is packed with information and has great educational value. It covers bracketed HDR, in-camera HDR, single-shot faux HDR, single-shot bracketed HDR, panoramic HDR and more! (see the complete pitch here). I asked their permission to post an expert of one of the tutorials on the blog as I think it's awesome stuff. Here we go.
HDR photography has become more and more popular due to recent technology. However, a great HDR image can be done with any DSLR camera. The process is actually pretty simple as long as you understand a few fundamental concepts and techniques. In this article, I will explain some basic information to help you reach your goal of producing a professional HDR photograph.
What is a “Stop” of Light?
One of the most important concepts in photography is the concept of a “stop” of light, which is a relative unit of light entering the camera. Without being able to actually quantify the amount of light within each stop, these measurements are calculated by the comparison between two or more units. This means that increasing by one stop doubles the amount of light, and decreasing by one stop cuts the amount of light entering the camera in half.
To explain this visually, I will show you a set of example images. Say you shot the image below and decide it is too dark. Here is that image below:
You can adjust your shutter speed or aperture to increase the amount of light that is being let in. Increasing by two stops would produce the image below:
Now you have a bright shot, but you realize you want it just a tad darker. Decreasing by one stop would produce the image below:
And the whole series together:
Obtain a Higher Dynamic Range
Now that you understand the concept of a stop of light, we will introduce a photographic technique called bracketing which is mainly used in HDR photography. Bracketed images are simply a group of images that differ by exposure values. Most DSLR cameras have a built-in function called “Automatic Exposure Bracketing” (AEB) to do this automatically. These combine exposures will give you a higher dynamic range for each scene since they will be combined during post-production. The combined series will then preserve detail in all areas in the photograph—not just the highlights or the shadows.
How AEB Works
Without AEB, you would have to take each exposure manually which can potentially cause problems with your bracketed series. Since AEB is customizable and automatic, it quickly shoots all exposures within less than a couple seconds. If you have to take each exposure manually, you have to capture and then adjust for the next image, and that takes time. If your subject isn't a still-life, then motion blur is most likely going to occur. The simple fact that you have to touch your camera each time you fire another shot risks disruption of the series by camera shake.
What is so great about the AEB function is that it allows us to tell our cameras to capture a group of images that differ by a specific exposure value spacing. It is customizable, so adjust the spacing value to your liking. Decide how many stops apart from each other to set your bracketing sequence depending on what range of exposures you want to capture. We typically set our cameras' AEB to what we refer to as a three-frame, two-stop bracketed sequence since this setting usually gives us a good range of exposures without missing any needed detail.
Understanding the concept of how light enters the camera is fundamental to producing professional HDR photographs. This information will help you when you begin to create each bracketed series for your HDR photographs. With bracketing, the best thing you can do is practice the technique. With more experience, you will master the techniques that will help you reach your HDR photography goals. After you've mastered bracketing, your next step is learn the processing side of HDRs, which we'll cover in another article soon.
About The Author
SLR Lounge is a a photography tutorial and inpiratioal blog. They cover everything from gear through inpirational posts to tip and tricks. Their DVDs and lightroom presets systems are one of the best in the industry.