DEIMOS will automatically adjust the instrument focus when the
observer changes from one filter to another. This process,
called "Filter-Focus Discipline", is accomplished by the
DREMEL daemon.
Procedure
When DREMEL is started it reads the filter focus offsets from
the tweak file. Whenever the filter position changes, DREMEL
will read the corresponding filter name, look up the
corresponding offset (which it stores in the keyword FOCUSOFF),
add that offset to the current value of the FOCUSVAL, and thus
derive the applied focus value DWFOCVAL. The explicit formula is:
FOCUSVAL + FOCUSOFF = DWFOCVAL
Fiducial
The R-band filter is the fiducial and thus the offset for this
filter is zero by definition. Offsets for other filters are
measured relative to this filter.
Defined Offsets
As of 2010-Sep-11, the offsets are as follows:
| Filter Name |
Filter Offset |
| B |
-100 |
| V |
-700 |
| R |
0* |
| I |
-300 |
| Z |
-400 |
| BAL12 |
-950 |
| GG400 |
-900 |
| GG455 |
-450 |
| GG495 |
-800 |
| OG550 |
50 |
| NB8580 |
-657 |
| NB8560 |
-570 |
Filter Focus Offsets
*Fiducial filter; zero offset by definition.
Tweak File
- /kroot/data/deimos/dremel.twk (on keamano)
- File containing the DREMEL startup data, including the
focus values.