Hi Robin
I reworked this one in ISIS and used their autocalibration for the Alpy.. the errors on the Balmer lines were an order of magnitude smaller (~0.23A for first 4 Balmer lines starting at Ha – it gets worse at blue end..)
Incidentally, I managed this only after reading the the thread in
http://www.spectro-aras.com/forum/viewtopic.php?f=8&t=1246&start=0
The nominal value of the Atik460 pixel size (4.54) is too big for me.. it works best with 4.45 (I wonder if there is a typo in their literature – swapping 4 and 5!?)
cheers
Kevin