The Assabet River has crested and now will slowly work its way back to its normal lazy ways, but for now it still is packing a punch.
I did two and a half studies of different exposures of the river, ranging from 1/1000 second to 8 seconds. The result is a rough guide for matching how the exposure times translate to particular moods that we might want to express from this rapidly churning water.
The first study is of a submerged island with water flowing around trees, starting at 1/1000 second and slowing down 1 stop at a time (essentially doubling the exposure time):
From 1/1000 to 1/60 we see the river abstracted in a “frozen” form. At 1/30 second the image changes to a different abstraction — one that implies fluidity. 1/15 through 1/2 second really appeal to me as a way of implying rapidly moving, turbulent water. Starting at 1 second the image of the river’s turbulence is slowly transformed into something that might be considered almost tranquil (as astutely noted in a comment by Rich Rosenbaum in my initial article)
The second study was of a rock in the middle of the river which is creating a very dynamic bit of turbulence. Because the situation around the rock varies so much, the first sequence shows two images at each exposure time starting at 1/1000 second down to several seconds. We then zoom into the rock and work our way back to 1/1000 second.
Despite being a very different subject I get more or less the same impressions from the same ranges of exposure times. So I’m becoming confident that I now have reasonable set of exposure guidelines I can apply to fast moving water to produce certain effects.
All of the images were captured on a Canon 5D Mark 2, 70-200mm f/2.8L lens, and processed with Lightroom. Some of the images were created using polarizing and neutral density filters. Fairly aggressive contrast tweaks were applied, plus a bit of vibrance, but they are otherwise unchanged. The videos were created with Lightroom 3 Beta, which has a great new feature that allows exporting slideshows as MPEG-4 movies (although I did have to transcode it to H.264).
The image at the top of the page was captured with a 16-35mm f/2.8L lens (at 16mm) with a polarizing filter. It had the same post-processing as the images in the video, but a localized adjustment was made to increase the exposure on the oak tree trunk.
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by Dave
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