Saturday, August 18, 2012

Managing dynamic range when photographing the sunrise or sunset

We're now deep in the dog-days of summer, when many folks in the northern hemisphere head for the beach.  If you're one of those people and you're reading this blog, then chances are you'll be visiting the shore with a DSLR over your shoulder or a point-and-shoot tucked into your beach bag. Having just returned from a family vacation on Delaware's eastern shore myself, I thought I'd share some thoughts about making what is perhaps the quintessential beach vacation photograph -- an image of the sun rising or setting over the ocean.

Photographing the sunrise or sunset over water presents two challenges: one technical and one creative.  On the technical side, choosing the exposure of any image that includes the sun necessarily involves some trade offs.  You'll need to find a way to manage the huge dynamic range of your scene.  On the creative front, let's face it, pictures of sunrises and sunsets over the ocean are about as cliche' as it gets. How can you make your image different from the rest?

Even when it's low in the sky, the sun is certain to be far brighter than any other naturally lit component of your scene.   It'll be so bright, in fact, that your camera's sensor cannot hope to capture detail in both the area near the sun and more dimly lit foreground subjects.  If you decide to expose the scene brightly the sun will appear as a poorly defined yellow blob, and you'll probably lose a lot of detail in the part of the water reflecting the sun as well, but you'll be able to see detail in the rest of the scene.  On the other hand, if you expose the image darkly, the sun will appear as a crisp ball, you'll be able to make out details in the clouds and water near it, and the colors will be nicely saturated.  But much of the foreground of the scene will appear in murky darkness and anything backlit by the sun will probably appear as a silhouette.

The following bracket of three exposures illustrates the kind of trade off we face.  These photos were taken a few seconds apart.  In each image the camera was set to f/20 and ISO 100 so that shutter speed determined the differences in exposure. Because the sun was moving in and out of clouds and the overall light levels were changing rapidly, I used aperture priority rather than manual mode to establish a base exposure.  I dialed in -2/3 of a stop of exposure compensation and bracketed exposures one stop above and one stop below this baseline.

At plus 1/3 stop over the camera's recommended exposure value, the foreground sandcastle is well exposed but much of the sky is blown out and the sun's dawn colors lack saturation.

At minus 1-and-2/3 stops below the camera's recommended exposure value, we can see a lot more cloud detail near the sun and the colors of the sky and water are nicely saturated.  But the foreground sandcastle is rather dim and the relative brightness of the sun draws the viewer's attention away from it. 

My baseline exposure of -2/3 exposure value represents something of a compromise.  The sandcastle is a bit brighter but the colors are less saturated and we lose some detail in the sky.

Exposure is always a creative choice, but this is particularly true for images that include the disk of the sun.  We rarely look directly into the sun, and when we do, our eyes are overwhelmed by it's brightness in much the same way our camera sensors are.  Thus, there is no sense in which we can say that a particular image exposure "looks right".  Rather, one must choose an exposure that matches the mood that one wants to convey.

There are, of course, technical means of compressing the dynamic range of an image so that the compromise one must make between sky detail and foreground exposure is less stark.  Setting your camera to save images in RAW format will afford you a bit more flexibility in managing dynamic range using post processing software.  Beyond this, you can blend multiple exposures to preserve both highlight and shadow details.  Largely automated high dynamic range (HDR) software such as HDR Efex Pro uses global algorithms to merge information from multiple images.   You can also manually composite different exposures together using layer masks in pixel editing software like Adobe Photoshop Elements. If you prefer to work behind the lens rather than behind your computer, you can also take measures to limit the dynamic range of the light entering the camera at the time of image capture.  A graduated neutral density filter can be used to dim the light from the sky, bringing its brightness closer to that of the foreground.  Or, working from the other direction, you can use flash or reflectors to bring up the brightness of foreground elements.

The photo up top represents an alternative way of dealing with dynamic range that requires no specialized equipment or software and that has the added benefit of hopefully making your sunrise/sunset image a little different from the rest.  In my opinion the sun is rarely a very compelling subject on its own.  It's a round undifferentiated disk that we see nearly every day.  Rather, what's beautiful about sunrises and sunsets is what the filtered light from the sun does to the rest of the scene.  Given this, I would argue that the it's not at all essential that the sun actually appear in your sunrise/sunset images  When composing your image, try placing a palm tree or a boat or a yuppie jogger between yourself and the sun.  By doing so, you dramatically reduce the brightness of the brightest part of your scene, which will give you a lot more flexibility in placing your exposure to match the desired look of the rest of the scene.

I wish I could say that the photo at the top of this post was meticulously planned, but it really wasn't.  I was taking brackets of the sandcastle about 15 minutes after the ones shown above.  The sun was higher in the sky and the morning's joggers and dog walkers were just beginning to arrive at the beach.  I saw this woman running down the beach and it was clear that she wasn't going to make any attempt to avoid running in front of my camera.  As she past, I snapped a bracket of three exposures.  As luck would have it, she passed in front of the sun just as the brightest of the three exposure was recorded.

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