def mtf_ts_to_dataframe(tan, sag, freqs, field=0, focus=0):
    """Create a Pandas dataframe from tangential and sagittal MTF data.

    Parameters
    ----------
    tan : `numpy.ndarray`
        vector of tangential MTF data
    sag : `numpy.ndarray`
        vector of sagittal MTF data
    freqs : iterable
        vector of spatial frequencies for the data
    field : `float`
        relative field associated with the data
    focus : `float`
        focus offset (um) associated with the data

    Returns
    -------
    pandas dataframe.

    """
    import pandas as pd
    rows = []
    for f, t, s in zip(freqs, tan, sag):
        base_dict = {'Field': field, 'Focus': focus, 'Freq': f}
        rows.append({**base_dict, **{'Azimuth': 'Tan', 'MTF': t}})
        rows.append({**base_dict, **{'Azimuth': 'Sag', 'MTF': s}})
    return pd.DataFrame(data=rows)
