switch between camera in key frame?

hi can anybody tell me how i can animate the camera at a point in my animation and at another point further return it back to the position it was before. ???

mean like at a point i want the camera to focus zoom on something and then return to normal view.
how can i achieve this cause when i do this with my camera it focus but when i add another key frame to make it return to normal view it ignore my previous key frame and does do what i want.

please help.

You can see the keyframes more clearly in the function editor. This way you can better control what is going on.