I was up on Millicent Rogers Road shooting Cottonwoods & Storm Clouds when the light rapidly faded as a line of solid cloud quenched the sun's fire.
I saw that the line of shadow which had just swept over me would soon cross the fields by these trees. I'd seen these trees and fields many times and had long-hoped that circumstance would someday provide a photo op: if I got lucky, that time was now. I threw my gear in the back seat, jumped in, flew down to the road, grabbed a place to park, and rushed the couple of hundred yards to the likely spot.
As it turned out, I had 2 minutes to set up, compose, set the exposure (manual), then wait... just as the shadow line swept over me and across the field – what a rush! In the next 40 seconds the scene changed from a foreground bathed entirely in soft light - to the trees being enveloped in shadow - the light extinguished.
This, somewhere in the middle, was exactly what I wanted.