Doc:
Issue
Date
Page
VLT-MAN-ESO-14650-4942
P96
24.06.2015
85 of 161
ESO, Karl-Schwarzschild-Str. 2, 85748 Garching bei München, Germany
Important warning
: because the detector is cooled by a Pelletier, it takes time to evacuate
the heating towards the cooling pipes that cool down the Pelletier itself. As a consequence,
every time a loop is started or the integration time is modified the first exposures will have a
higher background and noise than optimal. It is therefore recommended to take a series of 2
to 3 images per position/filter/exposure time.
The example (Antenna galaxy, B filter, 5s exposure time) below illustrates this effect of the
Pelletier cooling delay. More details appear in the second exposure while the seeing did not
vary.
First exposure of the series. The bkg is at 1800
ADUs and the RMS at 12 ADUs.
Second exposure, the bkg is now at 1711 ADUs
and the RMS at 6.5 ADUs.
Ideally, the dark should also be corrected from the images taken with this camera. However,
the dark frames are not taken as part of the calibration plan, therefore we strongly encourage
the users to request such darks to be taken during daytime if needed.