Right mouse Button and Mouse Movement for Zoom?

Hi there, the problem I have just now is I can’t get the camera to zoom in on the scene with the right mouse button held down whilst moving the mouse forward. At the moment my camera can zoom in with the W key and the mouse wheel scrolled forward. Not sure how I can apply the same effect with the use of holding down the right mouse button and moving the mouse forward. Can anyone help me out on this please?