This is one of those images that was created using nothing but luck. I was photographing a marshy area near Sturgeon Bay, WI, when the air suddenly filled with a few hundred geese taking flight from behind a tree line and out of my view. My D7100 was mounted on a tripod-supported Sigma 150-500mm zoom. I barely had time to loosen the head controls enough to get the rig pointed skyward. There was no opportunity to get an eye to the viewfinder or to adjust exposure for a relatively bright sky. I just clicked off three shots as quickly as the buffer would allow given all the other settings. Adobe Lightroom 5 saved the shadow detail. The camera was in aperture priority mode. ISO 200, Sigma 150-500 at 180mm, f7.7, 1/800th second. This was my first outing with the Sigma zoom, the results were above my expectations.