Dome flats give a measure of the pixel-to-pixel sensitivity variations over the CCD. The dome's white flat-field screen is not perfectly evenly illuminated by the lamps on the top end of the telescope, but the light goes through the slit, gets collimated, diffracted and re-focussed, so that is not a problem. We do not use the sky for this as you would get spectra of the Sun!
- Go behind the control room desk and check that the black rheostat is dialed fully anti-clockwise down to zero [[File:rheostat.jpg|50px]]
- Flip the switch in front of it to ''On''
- Dial the rheostat up to 220 V (do not exceed that value as you will blow the lamps)