NIRSPEC Filters

Filter Complement

Pupil stops needed for both AO and FEU modes are now installed in both filter wheels giving access to all filters below

SPEC Filter Wheel No. 1

L-Prime 3.420-4.120

M-Prime 4.570-4.810

KL 2.134-4.228

HeI 1.078-1.088

Kband-new 1.907-2.554

FeII 1.639-1.654

M-Wide 4.420-5.530

Diagram of Filter Wheel 1 Layout

SPEC Filter Wheel No. 2

NIRSPEC-1 (Y) 0.947-1.121

Yband-new 0.950-1.120

NIRSPEC-3 (J) 1.143-1.375

Jband-new 1.140-1.350

NIRSPEC-5 (H) 1.413-1.808

Hband-new 1.434-1.709

NIRSPEC-7 (K) 1.839-2.630

K 1.996-2.382

K-Prime 1.950-2.295

Diagram of Filter Wheel 2 Layout

Filter Transmission Profiles

Y-band	J-band	H-band	K-band

Download spreadsheet of SPEC filter transmissions

Filter Notes

Following the NIRSPEC Upgrade in Dec. 2018, filters are moved in four ways:

(1) Using the NIRSPEC Format Simulator (EFS) by selecting the desired filter and clicking "go" in setup mode.

(2) Using the NIRSPEC Mechanism GUI, by clicking on the Filter pull down and selecting a filter and stop.

(3) Using the command line to call a filter by name that gets paired to a 2nd default filter automatically. E.g. "filt m-wide", (sets m-wide and open, when not in AO), or "filt kl" (sets kl and ao-stop, if NIRSPAO)

(4) Using the command line to call a specific filter combination from each of the 2 science filter wheels. E.g "modify -s nsmotor scifilt1nam=open" & "scifilt2nam=nirspec-1"

As part of the Fiber Extraction Unit capability, new pupil stops were added to each of the two science filters which now accompany the smaller apperture AO-stops: named feu-stop.

Position	Motor Steps	Filter 1	Motor Steps	Filter 2
0	9200	Open	200	NIRSPEC-1¹
1	18200	Thin	9200	Yband-new⁵
2	27325	AO-stop	18200	NIRSPEC-3
3	36200	L-prime	27200	Jband-new⁶
4	45200	M-prime	36200	NIRSPEC-5
5	54200	KL²	45200	Hband-new⁷
6	63200	HeI	54200	NIRSPEC-7²
7	72200	FEU-stop³	63250	AO-stop
8	81200	FeII	72200	FEU-stop³
9	90200	Kband-new⁴	81200	K
10	99200	M-wide	90200	K-prime
11	200	Blank¹	99200	Open

Footnotes

Primary initialization position
Secondary initialization position
New FEU-stops (4.9mm) replaced older ones (8.1mm) in Feb. 2022, which had replaced Pa-beta and CO in Feb 2019
Kband-new filter replaced H2 in Feb. 2022
Yband-new filter replaced NIRSPEC-2 in Feb. 2025
Jband-new filter replaced NIRSPEC-4 in Feb. 2025
Hband-new filter replaced NIRSPEC-6 in Feb. 2025

Other Notes

Use the THIN blocker in combination with NIRSPEC-1, NIRSPEC-3, and NIRSPEC-5. 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, as the expense of elevated counts at the longest wavelengths.
The OPEN position in each wheel is Lyot stop.
The THIN position in Wheel 1 is a thin piece of clear PK50 glass used to block thermal leaks in NIRSPEC-1 through NIRSPEC-7. It also has a central obscuration (i.e Lyot stop) to block thermal emission from the telescope secondary. Testing with FEU fiber showed that a position of scifilt1raw=20200 (6.67 degrees from nominal) maximized the throughput in the FEU mode by offseting the central obscurration from the FEU beam.
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.