UIST has two 24-slot filter wheels which contain filters for both imaging and for blocking the spectroscopy grisms. The MKO consortium filter set is installed where possible (see the discussion of new JHK standards for example). Click on the filter name to see an image of the profile (where available). Text files are also available giving transmission profiles for some of the filters, contact Watson Varricatt. The table below lists the filter wheels’ population.

The “black blank” is used for darks. This mask is painted with NEXTEL. The other “blanks” in the wheels are uncoated aluminium.

NOTE: Filters are grouped together to avoid leaks from adjacent filters. So in other words, we avoid putting short-wavelength filters next to thermal filters. (However, tests using two blanks in slots 22, which were next to the Mp and M-spectral filters in slots 21, gave near-normal dark current of ~1.0 e-/sec in 100-second exposures.) 

9 January 2007 –

Wheel 1

Posn	Filter	50% Cut on	50% Cut off	Step val.
1	Open	–	–	14,700
2	Blank	–	–	.
3	Black blank	–	–	7,374
4	Y[MK]	0.966	1.072	3,707
5	Hartmann mask	–	–	40
6	Z[MK]	1.008	1.058	84,373
7	K_s_MK	1.990	2.310	80,706
8	Klong	2.019	2.434	77,039
9	1.57(cont) [MK]	1.561	1.583	.
10	FeII[MK]	1.630	1.656	.
11	2.248(S1)	2.234	2.269	.
12	2.248 MK	2.235	2.270	.
13	2.122(S1)	2.106	2.124	.
14	2.122 MK	2.103	2.134	.
15	BrG MK	2.150	2.182	.
16	CH4_s	1.550	1.657	.
17	CH4_I	1.617	1.730	.
18	2.27cont[98]	2.257	2.291	.
19	2.42CO	2.413	2.436	.
20	L'[MK]	3.428	4.108	.
21	M'[MK]	4.572	4.800	.
22	blank	—	—	25,701
23	PK50 2mm	—	2.7	22,034
24	Blank	–	–	18,267

Wheel 2

Posn	Filter	50% Cut on	50% Cut off	Step val.
1	Open	–	–	78,100
2	9.95mm circ aper	–	–	.
3	IJH blocker	0.90	1.82	.
4	B2 blocker	1.43	2.60	.
5	J-spectral	0.96	1.71	.
6	HK-spectral	1.58	3.38	.
7	H-spectral	1.27	2.50	.
8	KL-spectral	2.11	3.13	.
9	L-spectral	2.56	4.61	.
10	J[MK]	1.17	1.33	45,105
11	H[MK]	1.49	1.78	41,438
12	K[MK]	2.03	2.37	37,771
13	3.4nbL	3.379	3.451	.
14	3.5mbL	3.383	3.594	.
15	3.6nbLp	3.560	3.625	.
16	3.99(cont)	3.964	4.016	.
17	BrA	4.025	4.080	19,436
18	PAH MK	3.264	3.318	.
19	3.28″Dust”	3.250	3.305	.
20	3.05ice MK	2.970	3.125	.
21	M-spectral	3.5	6.0	4,768
22	Blank	–	–	1,101
23	PK50 2mm	—	2.7	85,434
24	blank	–	–	81,767

Wheel Movement 
Both wheels move in either direction. Consequently, if a required filter step value is greater than the current value, the wheel will move through increasing steps; if the required filter is at a lower step value, the wheel steps will decrease. This means that moving from Posn. 3 (the “black blank”) to any other filter in wheel 1 would move through the open position. Likewise, moving back to blank would move through the open position.

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History 
15 Dec 2008: PK50 filter is now added in combination with the “Y_MK” filter since the “Y_MK” is found to have a red leak. 
15 July 2008: PK50 filter is now added in combination with the “K_s_MK” filter since the “K_s_MK” is found to have a red leak. 
9 January 2007: Replaced two blank filters with Y-band and IJH spectral blocker (for use with the IJ and JH grisms). 
11 July 2006: The “Kshort” filter is replaced with a “K_s_MK” Mauna Kea Consortium filter. The existing PK50 filter is replaced with a new one (with the same specifications).

Previous filter wheel arrangement is available here.