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 | 20s |
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 |
ALFOSC Polarimetry overheads |
Rotating the retarder (FAPOL) | 2s |
Readout time polarimetry imaging (standard window) | 20s |
Readout time spectropolarimetry (vertical spectrum) | 40s |
Readout time spectropolarimetry (default, horizontal spectrum) | 13s |
NOTCam overheads |
Target acquisition imaging | 3min |
Target acquisition spectroscopy | 5min |
Focusing telescope | 5min |
Differential twilight flats (2 x 8 images per broad band filter) | 7min |
Readout array (controller) | 3.6s |
Clear array command | 3.5s |
Data file storage time (for 4 to 32 MB files) | 2 - 10 s |
Typical overhead for "exp,mexp,dark,mdark" (per exposure) | 13 s |
Typcial overhead for "frame t N" (t < 5s, N = 10) | 13 - 23 s |
Typcial overhead for "frame t N" (t > 5s, N = 10) | 10 - 15 s |
Telescope dither 10" (ag-off) | 3-6 s |
Telescope dither 10" (ag-on) | 5-15 s |
Telescope dither 240" (ag-on) | 8-20 s |
Lens wheel WFC -> HRC | 30s |
Lens wheel HRC -> WFC | 50 |
Filter, stop, aperture & grism wheels | 30 |
Internal focus change | 25 |
Wavelength calibration (H and K-band WFC) | 3.5min |
See the
NOTCam User's Guide for details and explanations | |
StanCam overheads |
Focusing telescope | 5min |
Flat fields | 5min |
Filter change | 30s |
CCD probe | 25s |
FIES overheads |
Focusing telescope | 10min |
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 30000 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.
