Filter Notes

As of September 2009, the standard for moving filters in NIRSPEC is to use the "filt" or "filter" commands from the command line. Previous observing scripts used the "fil1pos" or "fil2pos" keywords. These keywords still exist and should work when NIRSPEC is on RNAS (non-AO); however, the "filt"/"filter" combination is recommended.

The shell script "filter" uses the index positions as defined in the table below to move the two filter wheels. For instance, to use the KL filter, one types "filter 5 11" to move filter 1 to position 5 (KL) and filter 2 to position 11 (OPEN). To use the NIRSPEC-7 with the thin blocker (standard), one types "filter 1 6".

The shell script "filt" is a higher level script that interprets filter names then calls the "filter" script. To use the KL filter, one types "filt kl". The script knows to send filter 2 to the OPEN position when NIRSPEC is non-AO and knows to send filter 2 to the AO STOP when NIRSPEC is behind AO. To use NIRSPEC-7 with the thin blocker, one types "filt n7" or "filt n7 thin".

Position	Motor Steps	Filter 1	Filter 2
0	0	OPEN	NIRSPEC-1¹
1	9000	THIN	NIRSPEC-2
2	18000	AO-STOP	NIRSPEC-3
3	27000	L-PRIME	NIRSPEC-4
4	36000	M-PRIME	NIRSPEC-5
5	45000	KL²	NIRSPEC-6
6	54000	HeI	NIRSPEC-7²
7	63000	Pa-Beta	AO-STOP³
8	72000	FeII	CO
9	81000	H2	K
10	90000	M-wide	K-PRIME
11	99000	BLANK¹	OPEN

Footnotes

Primary initialization position
Secondary initialization position
AO-STOP replaced Br-Gamma in September 2009

Other Notes

Use the THIN blocker in combination with Nirspec-1 through Nirspec-6. The THIN blocker can be used with Nirspec-7, but it will cut off the long-wavelength end (>2.5 micron) of the Nirspec-7 passband. Without the THIN blocker, spectra taken in Nirspec-7 will cause persistence on the SPEC detector within a few seconds.
The THIN position in Wheel 1 is a thin piece of clear PK50 glass used to block thermal leaks in NIRSPEC-1 through NIRSPEC-6.
The OPEN position in each wheel is Lyot stop.
The BLANK position in Wheel 1 is a solid piece of metal. This "filter" choice is the only way to block the light path with a cold element, and thus is the only way to take a true dark.