Filters

As suggested already in 2006, NOTCam would benefit from an upgrade to the full near-IR broad-band filter set corresponding to the UKIRT photometric system ZYJHK used for instance in UKIDSS. This meant purchasing the new standard filters Z (0.84-0.93 $\mu m$) and Y (0.97-1.07 $\mu m$). After getting quotes from several companies, it was agreed to accept the offer from NDC Infrared Engineering. They had the Y-band filter in stock but the Z-band filter turned out to be a bit more complicated to make. On their second try they managed to make a Z filter with a much smaller red leak and also a relative high efficiency on $>$70%. The red-leak is significant, but after consulting some potential users we came to the conclusion that the expected effect on the data are acceptable. We do believe there are better Z-band filters available, but we expect those to cost as much as 5 times more and we consider that expected improvement not to warrant the price. We are current planning to install the new filters in January 2011. When we have determined the zero-points for these new filters they will be added to our Exposure Time Calculator

It was realized that the transmission curves published online for the NOTCam filters were not entirely consistent, in the sense that the plots were correct, while the data files had not been wavelength shifted to correct for the offset between using a pinhole and a slit for the calibration (with shifts ranging from 0.0015 to 0.0025 $\mu m$). After some detective work the problem was solved, and all the data files were corrected and a note about it was added to the web page.

Prompted by a user question regarding narrow-band filters mounted in the parallel beam, a note was added to the NOTCam filter web page with a recipe of how to calculate this shift.