and Image Quality at the William Herschel Telescope
The median intrinsic seeing at the WHT site is 0.69 arcsec, determined
from measurements with the ING DIMM seeing monitor between 1995
and 1998 (histogram). This is comparable
with statistics for the Mauna Kea and Paranal observatories.
The contribution from dome seeing is negligible
under normal observing conditions.
The optical quality and tracking
accuracy of the telescope are good, so that image widths close
to the limit imposed by the site seeing can be expected at the telescope
Accurate focus of the telescope is crucial if
optimum image widths are to be obtained. A new method
for optimising the focus is under test.
The seeing estimate provided from the WHT autoguiders tend to
over-estimate the true seeing. This is because the autoguider cameras
have an independent focus adjustment which is not always set optimally
for seeing measurements.
The median turbulence outer scale length is 15m (approx.).
This means that the seeing FWHM in the red and IR for WHT is likely to
be less than predicted by the DIMM.
| People | DIMM
| Comparisons | JOSE
| Dome |
Focus | Tracking