Not much to go on, a horrible picture, I know, but the best in the sequence that I got. (I was just getting there, unpacking the camera, looking around, and this guy shot by across the marsh. I just raised the camera and shot, hadn't even checked the setting yet.)

Turns out I was at 1/160th, not much use on a 300mm lens! (But it gave me an f:29 aperture!) Click for a bigger pic, which is a 1-to-1 crop of the frame, which shows how far away he'd gotten by the time I got the camera up. Anyway, I have a thought, but would like the collective to chime in for me.