Echelle image processing scenario we use:
First of all, one have to observe each object at least twice: this allows to remove cosmic ray hits traces with good assurance.
At first, we have to prepare good "bias" image - we make it by averaging all bias frames (cosmic ray hits traces removal will be done simultaneously). After that, we should subtract the bias image from each other images. Finally, we create the mask (in DECH95 environment) using standard star spectrum (carried out with short exposition) and after that - we can perform the extraction for each spectrum of the night (in DECH95 environment too). Each couple of spectra for each of object should be averaged with simultaneous removal of cosmic ray hits traces. One can do this procedure using 'ADD&CLEAN VECTORS' in the DECH95 environment. So, finally we have clean extracted and averaged spectrum of each object.