Kermit Filters

Filters available in Kermit. Solid lines are measured transmission curves.

Basic specifications and characteristics for the available filters are listed below. Click on a filter name to get a transmission curve.

Name

Measured
Central
Wavelength
(µm) FWHM

(µm) Cut-on
Wavelength
(µm)
Cut-Off
Wavelength
(µm)
Peak
Transmission
(percent) Notes
Source

J 1.258 0.296 1.110
1.406
85.3
Barr

H 1.664
0.298 1.515
1.813
84.7
Barr

K 2.165
0.327 2.001
2.329
92.9
Note 1 Barr

Name	Measured Central Wavelength (µm)	FWHM (µm)	Cut-on Wavelength (µm)	Cut-Off Wavelength (µm)	Peak Transmission (percent)	Notes	Source
J	1.258	0.296	1.110	1.406	85.3		Barr
H	1.664	0.298	1.515	1.813	84.7		Barr
K	2.165	0.327	2.001	2.329	92.9	Note 1	Barr

The transmission curves are re-digitized from printed plots supplied by the vendor, Barr. There are thus small errors introduced throughout the data set; if you care about accuracy at a level below a percent or so, beware!
I took the vendor-provided filter transmission curves (these are standard Barr astronomy J, H, and K filters, measured at 77K), digitized the transmission curves, and made the above measurements. I'll actually stick all this information onto the Kermit web page, plus the complete transmission curves. The above numbers describe the filters themselves only; for a proper calculation of the effective isophotal wavelength I'd need to fold in a model atmosphere, optics transmissions, and detector QE.

Note 1: Looking at those numbers, it seems we actually have what is usually called a "Kshort" or "Ks" filter, rather than a straight K, even though the Barr printout refers to it as a K filter. (Compare with the NIRC2 filter list, for instance, which shows K, Ks, and K'. )

This page last modified on August 3, 2005 by Marshall.