def Focal_length_eff(info_dict):
    """
    Computes the effective focal length give the plate scale and
    the pixel size.
    Parameters
    ----------
    info_dict: dictionary

    Returns
    ---------
    F_eff: float
        effective focal length in m
    """
    # F_eff = 1./ (info_dict['pixelScale'] *
    #              np.pi/(3600*180) / info_dict['pixelSize'])

    if isinstance(info_dict["focal_length"], dict):
        info_dict["foc_len"] = info_dict["focal_length"][info_dict["channel"]]
    else:
        info_dict["foc_len"] = info_dict["focal_length"]
    return info_dict