Nature caught me out on the night we visited Snake River Overlook, the Grand Tetons viewpoint made famous by Ansel Adams. The sky was flat grey, the light boring and the view marred by haze so, after taking a couple of shots, I packed up my tripod, changed lenses and wandered around taking pictures of the people who were there. The cloud cover on the western horizon must have been rather less because, about 10 minutes later, this started and we were treated to a spectacular sunset. Needless to say, the tripod was set up again rather quickly.
For the technically inclined...
