My camera script doesn't work like I want it to?

Like, I want it to show their camera at this point, but instead it makes them stay zoomed out the whole time. Help?

cam = workspace.CurrentCamera
cam.CameraType = "Scriptable"
focus = Vector3.new(0, 15.8, 0)
zoom = 70
zoomin = true

for i = 1, 200, 1 do
    if zoom == 20 then
        zoomin = false
    end
    if zoomin then
        zoom = zoom - 1 
    else
        zoom = zoom + 1
    end
    cam.FieldOfView = zoom
    pos = focus + Vector3.new(-50 + i/2, 20, -50)
    cam.CoordinateFrame = CFrame.new(pos, focus)
    wait()
end

wait(1)
cam.CameraType = "Custom"

I'm trying to make the player's camera continue to spin around a certain point.