I'm brand new to this. I'm using the EX1 for the first time and was wondering how the autofocus is affected by diffusion filters. Specifically, we'll probably use a tiffen soft fx 2 or 3. I should be fine pulling my own focus most of the time, but there will be times when the autofocus will be a big help. Any thoughts?
Shouldn't be affected at all. Also you shouldn't be using autofocus ever. Unless you like that 'searching for focus' amateur video look of course. :) Read into the manual about the manual focus assisted mode for the best look.
Yes. Although I can't advise you because I've no experience with heavy FX filters on the EX cameras, my reaction to your intention is to caution against using anything but a UV/protector filter or a IR filter if the situation requires it. My reasoning is because these days you can do so much to your picture in post production that it's better to shoot clean instead, thus giving you the most options and leeway after the fact. I think FX filters are a hold over from the days before NLE's evolved to what they are today. This is, of course, just my personal opinion.