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Flatfields
It is a common practice among IR astronomers to obtain flatfield images
by median filtering of dithered frames
since images are usually background-noise
limited with a high level of counts (thousands of counts).
For the K band (K, Ks, Kcont, brg..) it is however recommended to
take twilight or dome flats with the same exposure time
but with different levels of illumination.
For the dome flats this can be obtained by taking flats
- with all lights off
- with the flats' lamp on
The difference of the two
will give a flatfield free of telescope thermal emission.
Take a high number of flatfields of each kind in order to
decrease the noise.
Darks
Point sources
Extended sources
Sky frames
Observing scripts
