I was a still photographer at a music video when I lived in Texas, and I've done technical work for a sportscast and worked for several months at a TV station in Oregon. That's as close as I've come to an actual movie set.

I also write screenplays (none optioned/bought/produced yet), but from what I've heard, it's a Hollywood truism directors are famous for banning writers from sets. The directors have their own plans and ideas and don't want the writer interfering with them.

I can see why. If you're a director, why would you want the one person (or people) who knows the script, characters, theme and plot better than anyone there, at your disposal? Sheesh.

i was helping with a short movie being made last week. i direct the boulder asian film festival and being a screenwriter myself, organize a screenplay contest. each year the winner gets produced. this year, the guy who won has a son who is an up and coming tv producer in los angeles. he asked his son to come out and help on the production. in this case the screenwriter on set wasn't a distraction, since there was quite a bit of rewriting that happened in preproduction.

it is common for directors to rewrite on the fly without input from the writer - i know i've done that. my mission is always to maintain the integrity of the story even if characters need to be nixed, shots and lines eliminated, etc.

if you get a chance, read screenwriter william goldman's book, 'adventures in the screen trade" and "which lie did i tell - more adventures in the screen trade.' he writes about the times he's been on set for 'butch cassidy and the sundance kid,'.