def true_fov(M, fov_e=50):
    """Calulates the True Field of View (FOV) of the telescope & eyepiece pair 
    Args:
        fov_e (float): FOV of eyepiece; default 50 deg
        M (float): Magnification of Telescope
    Returns:
        float: True Field of View (deg)
    
    """
    return fov_e/M