docs: def download_cutout(self, reading, focus=None, needs_apcor=False):
          """
          Downloads a cutout of the FITS image for a given source reading.
  
          Args:
            reading: ossos.astrom.SourceReading
              The reading which will be the focus of the downloaded image.
            focus: tuple(int, int)
              The x, y coordinates that should be the focus of the downloaded
              image.  These coordinates should be in terms of the
              source_reading parameter's coordinate system.
              Default value is None, in which case the source reading's x, y
              position is used as the focus.
            needs_apcor: bool
              If True, the apcor file with data needed for photometry
              calculations is downloaded in addition to the image.
              Defaults to False.
  
          Returns:
            cutout: ossos.downloads.data.SourceCutout
          """
          logger.debug("Doing download_cutout with inputs: reading:{} focus:{} needs_apcor:{}".format(reading,
                                                                                                      focus,
                                                                                                      needs_apcor))
          assert isinstance(reading, SourceReading)
  
          min_radius = config.read('CUTOUTS.SINGLETS.RADIUS')
          if not isinstance(min_radius, Quantity):
              min_radius = min_radius * units.arcsec
  
          radius = max(reading.uncertainty_ellipse.a,
                       reading.uncertainty_ellipse.b) * 2.5 + min_radius
  
          logger.debug("got radius for cutout: {}".format(radius))
          image_uri = reading.get_image_uri()
          logger.debug("Getting cutout at {} for {}".format(reading.reference_sky_coord, image_uri))
          hdulist = storage._cutout_expnum(reading.obs,
                                           reading.reference_sky_coord, radius)
          # hdulist = storage.ra_dec_cutout(image_uri, reading.reference_sky_coord, radius)
          logger.debug("Getting the aperture correction.")
          source = SourceCutout(reading, hdulist, radius=radius)
          # Accessing the attribute here to trigger the download.
          try:
              apcor = source.apcor
              zmag = source.zmag
              source.reading.get_observation_header()
          except Exception as ex:
              if needs_apcor:
                  import sys, traceback
                  sys.stderr.write("Failed to retrieve apcor but apcor required.  Raising error, see logs for more details")
                  sys.stderr.write(traceback.print_exc())
              pass
          logger.debug("Sending back the source reading.")
          return source