Thanks PotH that is a better article all round.
I never said that a writer can't control a film, and I can imagine that the late Mr Crichton was better placed than most to negotiate contracts to his satisfaction,

but it isn't that common. If the film rights reverted, well things could certainly get interesting.
I had wondered for a while if the film rights were sold "freehold". Seems barmy that they could be open ended while the author's copyright is limited. So thanks for that insight..