Camaras

How can I do to implement camaras in my level.

I'm looking for basic camaras, you press a wall, and you see from certain camara, then, if you get back, you return to normal view. How can I do that?

I asume this is for a Zdoom wad therefor here is a brief tutorial with a demo wad on how this is done.

http://zdoom.notgod.com/zdkb/zdoom2.html

hope this helps