UIST: Engineering: Grism Wheels
UIST has two 9-slot grism wheels which contain the polarimetry prisms and the grisms for spectroscopy. The table below lists the grism wheel populations.
FILTERS: See the UIST filter-wheels web page for cut-on/cut-off wavelengths for the filters. Note that the short-/long- grisms are used in second order, so some of the blocking filter choices are driven by the need to block different orders (e.g. 2nd order lines between 1.34-1.51 passed by the B2 would appear in the short-K grism in 3rd order [at 2.00-2.26], so the short-K cutoff must be >1.51um; similarly, 2nd order lines between 1.58-1.67 would come through the HK filter and be seen by long-K in 3rd order [at 2.37-2.51], so the long-K blocker cut-off must be >1.67um).
WEIGHTS: These are for the grism AND the holder. The holders alone (with screws, clips, etc.) each weigh 124.2g.
REF: The reference number is etched onto the grism and the grism holder. The full reference number is 30a##m, e.g. for the short J the code is 30a54m.
1 May 2005 — Present
|Wheel 1||Wheel 2|
|4||Short L||59||217.4||L-spectral||4||HK||83||181.4||B2 (cgs4)|
|8||Long K||55||251.4||KL-spectral||8||Long L||58||235||L-spectral|
Movement between positions 5 or 6 and the other positions involves moving passed a datum switch.
11 April 2007: Installed new blocking filters for IJ and JH grisms. Was previously using PK50.
1 May 2005: New IJ and JH grisms were installed (this time made from KRS-5, like the long-/short- grisms). These replaced the bad IJ and the HK xdisperser. A second wollaston was also installed in wheel 2 (filling the spot vacated by the HK-low, which was to be used for x-dispersed spec.). Spec-pol should now be possible with all grisms. Note that the two wollastons should be identical (same design, manufacturer, etc.) The new IJ and JH grisms look good, though they give slightly out-of-focus spectra.
9 March 2004: The new zeiss grisms (below) were found to be faulty (poor throughput). These were removed today for return to Zeiss. Posns 2 and 7 were left vacant (i.e. holder installed but with no grism or blank).
1 March 2003: New HK low and IJ grisms (Zeiss – direct ruled infrarsill) were installed. These replaced hyperfine grisms that were found to be faulty.
Previous grism wheel arrangements: Pre-20050501. Pre-20040309. Pre-20030301.