Bob Atkins , May 03, 2002; 12:32 a.m.
"Evaluative metering is going to overexpose this and blow out the egret's feathers everytime"
Exactly. That's why you spot meter it and place it 1.5 to 2 stops over the camera (18% grey) reading (depending on just how much detail you want in the plumage). You can open up from the evaluative reading of course, but the problem is how do you know how much (if any) compensation the evaluative metering algorithm has already used? You can guess based on previous experience (or Art's previous experience!), but you never really know. It would depend on the relative size of the subject (Egret) compared to the rest of the frame and the compensation any particular evaluative metering system gave to a white object of that size and relative brightness at the position the Egret occupies. That's a lot of variables to try to guestimate!
Still, if it works, it works.