Forcing first person view?

I've seen it done on a few servers so I know it's possible but I just don't have a clue on how to do it. I only want to force first person view for about 30 seconds and the go back to standard where the player can choose either first or third person views.

Anyone know how to do this?

EDIT: I know this can be done in options but I am making a mission and would like all players to be switched to first person view for 30 secs.

0=[] spawn {while {time<30} do {sleep 0.05;if (cameraView=="EXTERNAL") then {vehicle player switchCamera "INTERNAL"}}}

I don't think the above will work as I want to switch players to first person at a certain point during the mission. Basically, the players are in a chopper and I don't want them to be able to switch to third person till they have disembarked from the chopper.

Sorry, I should have said that in the first post.

Create a trigger that activates at that certain point and have it run this:

0=[] spawn {while {vehicle player!=player} do {sleep 0.05;if (cameraView=="EXTERNAL") then {vehicle player switchCamera "INTERNAL"}}}

That works great! Will this work for all players or just the main player?

player refers to the player character on the client that it's used on, i.e. it works for everyone.