I read about film and film production a LOT. Probably more than any sane person would want to read about anything. When I get onto a set or start working on a some post production I like to feel that I am prepared, that I know everything it is possible to know about what I am going to be doing. But this knowledge is only a crutch, something to fall back on if everything is going wrong.
If the only thing I based my decisions on was the writings of others, then my work would inevitably be unoriginal. With most of the jobs in film (both on and off set) what I base my decisions on is what feels right, what my instinct tells me. When I choose a camera angle, when I place a light, when I make a cut in the edit suite, all of the things that I have read about what you should do can be thrown out of the window if something entirely different feels like the right thing to do. Improving these instincts is not as easy as accumulating knowledge. It cannot be learnt, it can only be practiced. I am in no way saying that study is unnecessary. You need that knowledge to fall back on when your own instincts are failing you. But I am saying that if you only ever paint by the numbers and never trust your own inclinations, then your work will always be stale and unoriginal.
The job of the focus puller is certainly one of the most under-appreciated jobs on a film set. A good focus puller frees everyone to do so much more than they would otherwise be able to. Blocking can be more elaborate, camera moves can be more elaborate, depth of field can be used more effectively, actors can feel their way through movements instead of having to robotically move through the scene. This basically adds up to the difference between a amateur looking film and a professional looking film. And all this comes from the feelings and instincts of the focus puller. I have only done a couple of difficult focus pulls in my time. Whilst it may look like the most boring job on set, I actually found to be one of the most demanding. There are only a couple of principles to fall back on and although you will probably be finding marks and getting your actors to hit spots, the transition between those spots is all down to instinct. Putting that much pressure on my instincts has a pretty unusual effect on me. On a recent film shoot I found myself stood in the rain, desperately shielding the camera with an umbrella and simultaneously trying to pull focus on Nikon stills lens, entirely off the sound of someone's footsteps. There really was no room in my head for anything else.