USAXS imaging sequence (plan)

[prjemian]

Step 3 of #26 (USAXS Imaging Operations)

3. At each q, we decide the number of filters that is required and the
   image acquisition time, and acquire 4 images. Immediately after
   tuning of the instrument, we acquire
   1. USAXS image (sample in the beam, with filter, beam on).
   2. Optics (sample not in the beam, with filter, beam on).
   3. Dark field (beam off).
   4. Flat field image (sample not in the beam, q = 0, with filter,
      beam on, image acquisition time may need to be shortened to
      prevent saturation).

[prjemian]

Excusing the obvious pun, looks like a plan.