chris, like jeff points out, the bret wood book is 15 years old, but IMHO it still stands as the best resource book on welles.
besides listing resources wood is a perceptive writer and his comments on welles were revealing.
welles learned everything from toland. toland was gracious enough to make welles a part of everything he did. under another cinematographer welles could have turned out to be another hollywood 'chair' director, but thanks to toland welles became a movie making machine, probably the best one the movies ever had.
i don't suspect that cortez was the camera man for all of ambersons. welles had a lot of problems with cortez and probably did a lot of it himself, and harry wild did a lot of it also. at the lilly collection (which came from richard wilson's garage) there are production stills of ambersons, and the picture of harry wild with welles has written on the back side in pencil, "harry wild, cinematographer on ambersons."
back to deep focus: means nothing unless unless you use it somehow. we see deep focus every day of our lives with our eyes. it's dificult to acheive on film because film only records 5 ev guide numbers, anything above or under is either too dark or blown out looking. so you have your set, your camera is set up for deep focus by shutting the lens to 16.5, or maybe even 32 which is radical. you turn up the lights. lots of lights.
through all the geography that your actors are going to cover on the set, the light can't vary or drop below those 5 ev clicks on the lens. the techs walk all over the set with meters, instructing assistants to move lights in or out. that is how they used to adjust lights. that is why they call it balancing lights, it's an intricate job of adjusting over and over till it's all balanced in the geography the actors will travel. that is why welles wanted it. it was a pain in the ass to do and not a big deal, unless it was used as welles used it to say something.
in that scene that kane walks to the window and back, there is not a big variation of light, he does not walk through shadows, it's evenly lit all the way to the window and back, meaning welles insisted all the lights hit that huge set with the same intesity. also, from one ev number to the next the amount of light that hits the film doubles, you will see a variation. that makes that deep focus window walking scene in kane incredible.
or i could be completely wrong about everything.