Part 10 - Exposure Bracketing (The Photographer's Safety Net)

One well-known photojournalist and celebrity photographer whom my lab served for many years had a unique strategy for ensuring that his most important shots were always exposed properly. He would allow the camera to determine a correct exposure and then take this first picture. To be safe, he would then set his camera on manual and proceed to shoot one more additional picture at every half f/stop setting on his camera. This resulted in 20 or so exposures of the same scene -- each at a different f/stop setting. His logic was that "somewhere in that collection of images was the correct exposure." He would let the lab make the final determination as to which frame was best for printing. Obviously, he wasn't paying for the film.

This is an "overkill" example of one of the oldest techniques in a professional photographer's tool kit -- bracketing. Bracketing is the taking of a series of photographs of the same scene at different f/stops and/or shutter speeds to ensure a usable/printable image is captured. This series typically includes intentional over and under exposed frames. Bracketing doesn't reflect on a photographer's knowledge of the craft, but is intended to be a safety net when the shot is important, a once-in-a-lifetime opportunity or difficult to replicate.

Think about your own photography: There are probably instances where you will only have one chance to take a picture, or you know you'll never return to a particular site. Having those extra shoots at different f/stops or shutter speeds is an easy way of returning home knowing that the image you envisioned is on your data card. Besides, digital film is nearly free. Extra exposures cost nothing.

Today's DSLR camera manufacturers usually include a process for automating the bracketing process among their shooting options (look up the term bracketing in your camera's manual). If your particular DSLR does not have a bracketing function, you can always:

• Use your camera's exposure compensation function to force an under and over exposure
• OR set the camera on manual and create your own bracketing series.

Given the flexibility of the RAW data format that I recommend using, I suggest a bracketing series that includes 3 photographs:

1. the exposure you have determined is ideal (see my Posts 1a and 1b on Exposure is Everything).
2. a second exposure that is intentionally 1 stop overexposed.
3. a third shot that is intentionally 1 stop underexposed.

Exposure #1 - Normal

Exposure #2 - One stop overexposed

Exposure #3 - One stop underexposed

Of course, you can set up your own series of bracketing shots that can include 4, 5, 6 or more exposures, but 3 should usually provide a large enough safety margin.

There is another advantage of learning how to bracket exposures now. At some point, you might want to learn about, and experiment with, HDR photography (high dynamic range). Bracketing is fundamental to this increasingly popular photographic technique. HDR will be the subject of a future post.

Setting up auto bracketing on DSLRs varies slightly depending on the manufacturer. However, there are enough similarities between models to consider that the following Canon example is typical. Refer to your manual for the specific procedure for your camera.

My Canon menu screen. AEB is the selection on this camera (auto exposure bracketing).

Notice the white rectangle under the zero (0) AEB setting. This indicates that the camera is currently set for NO auto bracketing. Pressing the "Set" button selects AEB and allows the bracketing series to be set.

AEB is now selected and the 1 stop exposure series is indicated.

After pushing the "Set" button on the command dial, I can now turn the command dial (largest dial on the back of this Canon model) to the bracketing exposure series I want to use. In this case, the exposure series is indicated by the three white rectangles appearing under the numbers -1, 0, and +1. The camera is now ready to take a series of 3 exposures at the normal, under and over exposure settings I selected.

The shooting mode determines exactly how these 3 exposures will be taken:

• In single frame mode, the camera will require you to push the shutter button 3 times (once for each exposure)
• In continuous mode, the camera requires you to push and hold the shutter button while the camera automatically takes the three exposures.
• In self-timer mode, the camera will wait 10 seconds (or the time lapse you chose to enter) and then automatically take the three exposures.

Hopefully your camera is mounted on a tripod for the bracketing series. If possible, use a remote shutter release for the first two options to minimize camera shake. Using the self-timer mode also eliminates any camera shake that physically pushing the shutter button would normally induce. (Again, these are good habits to get into if you want to experiment later with HDR techniques.)

In every case, the end result will be three exposures of the same scene. Each image will vary by exactly one f/stop to provide a selection of exposures when you edit the pictures on your computer. If you were careful when determining the original "normal" exposure, one of these photographs will more than likely be optimal.

Something to consider when bracketing: Read the camera manual carefully and understand how your camera makes these exposure decisions. For example, if depth of field is critical to your picture and the camera creates these three exposures by changing the f/stop, your depth of field will change with each exposure. The Canon camera I used in this example changes the shutter speed to create the over and under exposed frames. As a result, my depth of field remains constant, but my ability to stop action changes slightly with each exposure. (In this case, the over exposed frame will use a slower shutter speed while the under exposed frame will be taken with a faster shutter speed.) Some cameras allow you to specify and control these variables. So read your manual.

Bracketing is certainly not a requirement in photography, but for those just getting started (and for many of us pros), it is a welcome safety net for those priceless photographic opportunities.

Finally, even if you decide not to bracket a scene, it's a wise precaution to take an extra picture or two of those important scenes. You just never know when that duplicate image will be needed because something unexpected changed during the first shot -- the subject moved, the camera moved, the light changed, the subject blinked, a cow walked in front of your camera, etc.

If you have questions or comments, please let me know. You know where to find me.