One little question on post production, you mentioned "Then do the x-dissolve thing in post to cover the fiddling around." I'm not familiar with this idea, what do you mean - I'm just starting out shooting jpeg stills and editing via actions in photoshop. [a href=\"index.php?act=findpost&pid=200617\"][{POST_SNAPBACK}][/a]
In a running movie made of stills you will sometimes get gross exposure changes. If you are very careful about preparing your original stills in PS, this will not be much of an issue. But in those occasions where you wind up with a sudden dramatic exposure or qualitative change in the running movie shot, you can "cut" the movie into two pieces at that exact point, then connect the two pieces via a cross dissolve or perhaps 2 seconds length. A cross dissolve requires you to slide the next piece of film a few seconds backwards and "overlay" it over the preceding piece of film, so you lose a short duration of time as well. During the cross dissolve we slowly blend between the two pieces of film which takes away the sudden impact of the exposure change. The bump gets stretched out over 2 seconds instead of 0 seconds so its much less noticable.
All the editor programs let you do a cross dissolve. With Windows Movie Maker there is a menu somewhere that lets you change the default 1 second cross dissolve to 2 seconds or whatever you want. 1 second is probably a little too short for this kind of use.
In regards to the polarizer, the best time to start the rotation is just a few minutes before the sun touches the horizon. It takes about 4 or 5 minutes for the sun to disappear after that first touch, then there is a much slower rate of exposure change. You want to bias the starting position of the polarizer so you sort of eas-into the range of increasing polarizer effect which you should reach during the time the sun is grazing the horizon. The biggest exposure issue is that the sky darkens much slower than the ground, you quickly get into a situation where you can't find an exposure that works for both sky and ground. If you can shoot raw you will be able to tease a slightly better overall compromise exposure than if you shoot jpegs, but of course your post processing effort will escalate dramatically.
I like the way the Adobe Capture Raw program lines up the input files in a row. By watching how the levels graph animates as you flip from picture to picture you can get a really good idea of how the images themselves with animate (or jump, or flicker, or whatever) on your final film. That levels graph is the best way I know to equalize frames for movie work.
Do not expect success on your first attempt, these kinds of shots take a lot of experimentation. If I were you, I'd probably see what could be done with autoexposure alone on the first attempt, and count making a few cross dissolves and lots of post processing twiddling.