If poor weather conditions during twilight prevent you from obtaining sky flats, dome flats can be used instead. These can be obtained at any time by imaging a "uniformly" illuminated screen in the dome in the following way:
# Follow the [[#Start-up recipe|facility start-up procedure in Section~\ref{sec-facstartup}, ]] but there is no need to hook the outside doors open and '''do not open the dome'''. '''Remember to open the mirror covers.'''# Follow the appropriate [[#Instrument start-up procedure|'''instrument setup''' ]] procedure in Section~\ref{sec-inststartup}.
# '''Switch on the domeflat lamp''' by turning the dial on the wall between the North pier and the blue console.
# '''Rotate the dome''' to an azimuth of 180°, such that the lamp on the catwalk illuminates the round, white screen on the dome as uniformly as possible.
You may need to adjust the dial on the incandescent lamp between filters to achieve manageable exposure times. With STE3/4, keep exposure times ≥1s to allow the shutter time to open and close.
== Observing recipes: on sky ==