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Dark current calibration

Dark current exposures are required to correct for the thermal release of electrons, which are accumulated during the exposure. The dark current is linear in time but the amount is varying from pixel to pixel. It is therefore necessary to obtain a dark current image for every exposure time and every binning used during observations. Dark current exposures can be made during daytime. As the longterm behaviour of the dark current is unknown it is recommended to make dark current images after each observing night. A dark current image with zero exposure time is also known as bias frame.

Switch on telescope electronics: Press operation on in the control panel to switch on the main controls. Hydraulics can be left 'off', but the main camera is to be cooled to operating temperature.

Go to the main camera section:

Setup of the main camera: Choose an exposure time and binning. Recall that you need dark current images for any combination of these settings used during observations.

Make a sequence of dark current exposures: Select exposing/save in the misc pull-down menu. Record at least 3 exposures to allow filtering of cosmic ray hits.

The master dark current image is obtained during the reduction process by averaging (use the median!) of the sequence of dark current exposures.


next up previous contents
Next: Flat-fielding Up: Calibration exposures Previous: Calibration exposures   Contents
Dieter Engels
2003-01-15