I happened to look out of my hotel room window Thursday morning and saw one of the reddest sunrises I have ever seen. The sky literally looked like it had caught on fire. I quickly grabbed my camera, attached my 70-200mm lens, and began shooting. Because I was handholding the camera, which is something I rarely do, I set the camera on aperture priority and my ISO on Auto. This allowed me to set the aperture while the camera picked the slowest shutter speed possible for the focal length I selected and then adjusted the ISO automatically based on the shutter speed and aperture.
For this image, I set the aperture at f/8, which is generally the sharpest aperture for the lens I was using. The camera then set the shutter speed at 1/80 second and raised the ISO to 1250 in order to maintain the selected shutter speed and aperture combination. Because the ISO was so high, the picture contained a great deal of digital noise, but I was able to remove it by adjusting the Luminance noise reduction slider in Lightroom.
Settings: Canon 5D Mk II, 100mm, 1/80 sec, f/8