def decode_aperture_chunk_data(chunk_data_aperture_byte):
    """
    Convert value provided in byte 7 of chunk data to FStop number

    Formula provided on page 100 of GigE_Features_Reference.pdf (v5.3.2)
    https://www.alliedvision.com/fileadmin/content/documents/products/cameras/various/features/GigE_Features_Reference.pdf

    Parameters
    ----------
    chunk_data_aperture_byte: int 0-255
        value of chunk data byte 7, called chunk_dtype['lens_aperture']

    Returns
    -------
    fstop: float

    """
    return 2**((chunk_data_aperture_byte - 8) / 16.0)