Nordic Optical Telescope

Aligning echelle grisms, slits and cross dispersers

As the Echelle orders appear very curved on the chip, and as the Echelle slits are very short, there is no real reason for aligning any of these.

However, it is important to define the center of the slitlet in the ~obs/alfosc/slitpos.def file (use alfosc.edit-slitpos). The position of slit center (in CCD pixel coordinates) must be measured from a unbinned full-frame slit image, without a filter in the ALFOSC beam. Use the ThAr lamp with 0.2 sec exposure.

Here the link to the infamous obsolete instructions.