How can I find the magnification multipler from FOV?

I am trying to figure out a way to get the magnification multiplier from camera FOV, but all I managed to find was this code snippet where you can find the FOV value for the targeted magnification:

         var magnification = 1.0f;
         var factor = 2.0f * Mathf.Tan(0.5f * 60f * Mathf.Deg2Rad);
         var zoomedFOV = 2.0 * Mathf.Atan(factor / (2.0f * magnification)) * Mathf.Rad2Deg;

I seriously cant find any way of finding the magnification with googling around.