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Order-blocking, Acquisition, and Neutral Density Filters

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The filters listed below are used during spectroscopy for order-blocking and (with the exceptions of M, L, and XD) for acquisition. For acquisition they provide complete and unvignetted views of the acquisition "keyhole," whose dimensions are shown here.

Order-blocking Filters for Spectroscopy and Acquisition
Filter Name Diffraction
Wavelength range Transmittance plot
measured in GNIRSa
Transmittance numerical data
measured in GNIRSa
Transmittance curve
from manufacturer
Gemini ID
Mb 1 4.4 - 6.0um - - yes G0501
Lb 2 2.8 - 4.2um - - yes G0502
K 3 1.91 - 2.49um yes yes yes G0503
H 4 1.47 - 1.80um yes yes yesG0504
J 5 1.17 - 1.37um yes yes yesG0505
X 6 1.03 - 1.17um yes yes yesG0506
XDb 3-8 (cross-disp) 0.9 - 2.56um - - yesED316
ascaled to transmittance of the XD filter in the relevant wavelength interval
bNot used for acquisition

Acquisition Filters (narrow band)
Filter Name Width Central Wavelength Transmittance plot
measured in GNIRS
Transmittance data
measured in GNIRS
Transmittance plot
from manufacturer
Gemini ID
H2 1.5% 2.122um yesa yesa - G0521
PAH 1.5% 3.295um yesb yesb - G0523
ascaled to transmittance of the XD filter in the relevant wavelength interval
bscaled to transmittance of the L filter in the relevant wavelength interval

Acquisition filters are defined in acquisition observation sequences - see the OT Details and Acquisition pages for more information.

A neutral density filter used for acquisition of very bright objects is also available for use (currently with the H and H2 filters only). Its properties are summarized below. Because the ND filter offsets images by ~0.1 arcsec perpendicular to the slit, It should not be used if the slit width is 0.45 arcsec or less, unless the neutral density is also used for spectroscopy.

Attenuation by Neutral Density Filter
1.1µm 1.25µm 1.65µm 2.2µm 3.5µm 4.8µm
350X 250X 170X 130X 100X 85X