News for SM & VM observers
Please note that we are presently experiencing some difficulties with the chopping and counter-chopping of NACO.
While the problem is under investigation, please be informed that the behaviour of the system is quite erratic and thus difficult to predict.
However, it is advised, in order to improve chances of success, to use a small chop throw (<= 10" - 15" max) and avoid chopping at an angle of 90 degrees.
The SDI mask has slid out of position and thus appears rotated by almost 45 degrees. As a consequence the untilted FOV is smaller than expected. (See Fig. 1 for illustration).
Experienced SDI users advise to set the the OFFSET dither box size to no more than 0.2x0.2" (just enough to get rid of bad pixels).
Fig. 1: Illustration of the SDI FOV