[picture of a person holding a DEIMOS grating]
DEIMOS gratings are fairly large and heavy. They are also extremely expensive and fragile. Please exercise the utmost caution in handling these items.
Each grating lives permanently in a "cell" which is labelled with a permanent barcode label. The cell is inserted into the grating "slider", which travels back and forth on the grating select drive and also tilts independently. Only two of the four grating positions in DEIMOS are actually used for removable gratings. The third is a permanent mirror which does not tilt, and the fourth was for a grating which will not be installed.
Hence there are only two gratings for DEIMOS. Both are accessed through the same hatch. [picture of DEIMOS grating access hatch 3+4]
To change a grating, rotate the instrument to [insert PA here]. Open the hatch. Use the pushbutton control to move the select mechanism to Unload Position 3 or Unload Position 4. [photo of pushbuttons]
Carefully remove the installed grating and replace it with the desired one. When done, you may as well scan the grating right away; the grating select stage is slow and unlike the filter wheel there is no efficiency to be gained by separating the loading and scanning activities. It can be a bit tricky to get the scan beam lined up with the grating inside the instrument -- try putting the bargun fairly far inside the instrument, as if it were a flashlight.
The bargun will beep when it is successful in reading the label. Dremel will buzz once, briefly, when it recognizes the grating.
When done, close the hatch and lock it.