This photo was taken from the rear car on the Durango-Silverton Narrow Gauge Railroad in Colorado. The camera was a Nikon D7000 with a Nikkor 16-85 mm VR lens at 50 mm. The exposure was f/7.1 and 1/1250 sec (ISO 800). The leisurely trip covers about 45 miles in distance and 2800 feet in elevation providing opportunities for scenic as well as rail shots. Railroad aficionados might know the reason for venting the steam. (Maybe to blow out scale deposits?)