© 2009 Craig K. Gowens
Just a short hike off the Going-to-the-Sun Road just west of St. Mary Lake is the St. Mary Falls of the St. Mary River. The river is fed by glacial melt from the Jackson and Blackfoot Glaciers. As with many glacier fed bodies of water, the river contains rock flour, rock ground so fine it remains suspended in the water, which defracts light towards the blue end of the spectrum giving the water a blue-green color.
This is the horizontal view of a shot I posted on Flickr earlier. Getting a slow shutter speed to get the graceful, silky effect on the water was difficult with such bright sunlight. Moreover, there was a huge differential in lighting from the left wall of rock in the shadows and the right which had full sun. This was shot at ISO 50 at f/11 with a polarizer and both 2x and 4x neutral density filters. The exposure bracketed shots used to create the tonemapped HDR had shutter lengths of 1.3 sec, 1/3 sec and 5 sec. (Note: This was done on a manual focus Contax Zeiss 35-70mm f/3.4 lens with a Y-to-EOS adapter and as such the lens doesn't report the correct focal length and aperture used. By default the adapter reports a 35mm focal length, the wide end of this lens, and an aperture of f/3.5, the len's maximum aperture. This was shot at 35mm.)