Below you find tables with typical times for the different
operations when observing at the telescope.
The execution time for
a set of exposures as defined in an observing script is given as
output from the script
generator. The read-out time of the detector is included in the
execution time, but is less for a windowed CCD (see instrument web
pages ALFOSC,
FIES,
MOSCA,
StanCam). Sum up
the execution time of the observing script with the times needed for
other operations (e.g., acquire the target, focus the telescope) to
estimate the total execution time for a specific observation.
| Function | Time |
Telescope overheads |
Target acquisition (imaging) | 3min |
Target acquisition (spectroscopy) | 5min |
Small step dithering (no autoguiding) | 6s |
Small step dithering (autoguiding) | 15s |
Large step dithering (beam switching, no autoguiding) | 20s |
Mirror covers open (baffle lamp) | 1min |
Mirror covers close (baffle lamp) | 1min |
FASU overheads |
Changing filter (typical) | 20s |
Changing filter, adjacent slot | 6s |
Mirror motion (calibration lamps) | 13s |
ALFOSC overheads |
Changing slit/filter/grism | 25s |
Focusing telescope | 5min |
Flat fields (typical time for 3 images in one filter) | 8min |
Readout times (see this table for different windows) | |
ALFOSC Polarimetry overheads |
Instrument and telescope setup | 50s |
Rotating the retarder (FAPOL) | 2s |
Readout time polarimetry imaging (standard window) | ~ 6s |
Readout time spectropolarimetry (default, vertical spectrum) | ~ 10s |
NOTCam overheads |
Target acquisition imaging | 3 min |
Target acquisition spectroscopy | 5 min |
Focusing telescope | 5 min |
Differential twilight flats (2 x 8 images), per filter/camera setup | 8 min |
Readout array (controller) | 3.6 s |
Clear array command | 3.5 s |
Data file storage time (for 4 to 32 MB files) | 2 - 7 s |
Readout overhead for "exp,mexp,dark,mdark" (per exposure) | 8-9 s |
Readout overhead for "frame t N" (t < 5s) | 5-7 s |
Readout overhead for "frame t N" (t > 5s) | 4-5 s |
Telescope dither 10" (ag-off) | 3-9 s |
Telescope dither 10" (ag-on) | 7-9 s |
Telescope dither 240" (ag-on) | 8-20 s |
Lens wheel WFC -> HRC | 30 s |
Lens wheel HRC -> WFC | 50 s |
Filter, stop, aperture & grism wheels | 30 s |
Internal focus change | 25 s |
notcam.easy-calib (1-5 wavelength regions for WF-cam)
1 argon, 1 xenon and 3 halogen per region | 2 min per region
+ 1.5 min |
notcam.easy-calib (1-3 wavelength regions for HR-cam)
1 argon, 1 xenon and 3 halogen per region | 5 min per region
+ 1.5 min |
Wavelength calibration (H and K-band WFC) | 3.5 min |
See the
NOTCam User's Guide for explanations of overheads | |
StanCam overheads |
Focusing telescope | 5min |
Flat fields | 5min |
Filter change | 30s |
CCD probe | 25s |
FIES overheads |
Target acquisition | 2-5min |
CCD probe | 20s |
Fiber mask: typical | 20s |
Fiber mask: worst case = between fibers #1 and #2 | 85s |
Fiber calibration arm: typical | 12s |
Fiber calibration arm: worst case = from fiber #4 to #1 | 65s |
ThAr calibration exposure, all overheads included | 2m |
FIES & StanCam overheads |
CCD probe | 20s |
Note that we have used 120 seconds as an upper limit for faint arc
line and flatfield spectra.
For the flatfield lamps the exposure times
aim for about 60000 ADU, and the expo times scale reversly with slit
width (the values below are for a 1 arcsec slit).
Exposure times for the Halogen lamps aim for 35K peak counts.
Exposure times for the ThAr lamps aim for 15K peak counts in the blue.
All values are for an unbinned CCD.
Please note that the exposure times needed for the FIES calibrations
are fluctuating notoriously, and need to be checked at the start of the run.
