NOTCam Filters
NOTCam contains two filter wheels each with 16 slots of 25mm diameter.
Thus up to 30 filters may be installed at any given time. The filters
are located in the parallel beam of the instrument, close to the pupil
plane, and all filters are tilted by 6 degrees to reduce internal
reflections (see bottom of this page for details).
Note that as of 10/6/2004 all NOT ID numbers of the NOTcam filters
were upped by 200 in order to achieve uniqueness in the NOT filter
numbering.
Together with a number of institutes the NOT was participating in a
group filter purchase (~1998) from NDC IR Engineering (UK) of a set of
new standardized IR filters named the
Mauna Kea Observatories Near-Infrared Filter Set (check this link
for specifications as well as isophotal wavelengths, isophotal frequencies,
and flux densities for Vega). Unless otherwise stated in the Comment
field, the filters in the table were purchased from NDC IR Engineering
as part of the Gemini consortium group purchase.
NOTCam
Filter # |
status |
Name
(click for details) |
Bandpass (µm) |
Transmission
Curves |
Comment |
on |
central |
off |
| 201 |
Mounted |
J |
1.165 |
. |
1.328 |
gif, ascii |
NOTCam standard J |
| 202 |
In lab |
J (spare) |
1.167 |
1.250 |
1.334 |
gif, ascii |
Sent to CPH for measurement |
| 203 |
Mounted |
H |
1.484 |
. |
1.780 |
gif, ascii |
NOTCam standard H |
| 204 |
Stored |
H (spare) |
1.487 |
1.626 |
1.766 |
gif, ascii |
|
| 205 |
Mounted |
K' |
1.950 |
. |
2.290 |
gif, ascii |
|
| 206 |
Stored |
K' (spare) |
1.950 |
2.115 |
2.280 |
gif, ascii |
|
| 207 |
Mounted |
Ks |
1.999 |
2.140 |
2.282 |
gif, ascii |
NOTCam standard K for imaging |
| 208 |
Mounted |
K |
2.038 |
2.200 |
2.363 |
gif, ascii |
NOTCam standard K for spectroscopy |
| 209 |
Mounted |
Br  |
2.147 |
2.163 |
2.179 |
PDF, ascii |
|
| 210 |
Mounted |
K continuum |
2.251 |
2.267 |
2.284 |
PDF, ascii |
|
| 211 |
Mounted |
H continuum |
1.562 |
1.574 |
1.586 |
PDF, ascii |
|
| 212 |
Mounted |
[Fe II] |
1.632 |
1.645 |
1.657 |
PDF, ascii, |
|
| 213 |
Mounted |
He IA |
1.070 |
1.079 |
1.089 |
png, ascii* |
*Measured warm at IAC (0.3-2.6 microns) |
| 214 |
Mounted |
Pa |
1.086 |
1.094 |
1.102 |
ascii* |
*Measured warm at IAC (0.3-2.6 microns) |
| 215 |
Mounted |
J-continuum |
1.201 |
1.211 |
1.221 |
PDF, ascii, ascii*
|
*Measured warm at IAC (0.3-2.6 microns) |
| 216 |
Mounted |
Pa |
1.277 |
1.287 |
1.296 |
PDF, ascii, ascii*
|
*Measured warm at IAC (0.3-2.6 microns) |
| 217 |
Mounted |
He IB |
2.056 |
2.071 |
2.086 |
PDF, ascii |
|
| 218 |
Mounted |
H2  =1-0 S(1) |
2.101 |
2.118 |
2.133 |
PDF, ascii |
|
| 219 |
Mounted |
He IC |
2.167 |
2.184 |
2.200 |
PDF, ascii |
|
| 220 |
Mounted |
H2 =2-1 S(1) |
2.233 |
2.251 |
2.268 |
PDF, ascii |
|
| 221 |
Mounted |
CO (2-0 bandhead) |
2.271 |
2.288 |
2.305 |
PDF, ascii |
|
| 222 |
Stored |
Yn |
1.004 |
1.028 |
1.053 |
png, ascii* |
Check note!, *Measured warm at IAC (0.3-2.6 microns) |
| 223 |
Mounted |
CH4 s |
1.543 |
1.599 |
1.655 |
PDF,ascii |
|
| 224 |
Mounted |
CH4 l |
1.624 |
1.680 |
1.736 |
PDF,ascii |
|
| 225 |
Order cancelled |
Grism 1 |
1.000 |
1.300 |
1.600 |
. |
|
| 226 |
Stored |
Grism 2 |
1.400 |
1.950 |
2.500 |
. |
|
| 227 |
Stored |
[Fe II] |
. |
1.644 |
. |
. |
From Barr, use #212. |
| 228 |
Mounted |
[Fe II] Continuum |
1.682 |
1.689 |
1.696 |
PDF,ascii |
From Barr. |
| 229 |
Stored |
H2 =1-0 S(1) |
. |
2.122 |
. |
. |
From Barr, use #218. |
| 230 |
Mounted |
H2 =1-0 S(1) Continuum |
2.077 |
2.087 |
2.097 |
PDF,ascii |
From Barr. |
| 231 |
Stored |
1754/10 |
. |
1.754 |
. |
. |
Belongs to B. Thomsen |
| 232 |
Returned |
1004/10 |
. |
1.004 |
. |
. |
Belongs to G. Östlin |
| 233 |
Returned |
1012/10 |
. |
1.012 |
. |
. |
Belongs to G. Östlin |
| 234 |
Returned |
1029/10 |
. |
1.029 |
. |
. |
Belongs to G. Östlin |
| 235 |
Returned |
1020/10 |
. |
1.020 |
. |
. |
Belongs to G. Östlin |
| 236 |
Mounted |
Y |
0.944 |
1.020 |
1.097 |
png1,
png2,
png3,
ascii, ascii*
|
From NDC Sep-2010. *Measured warm at IAC (0.3-2.6 microns) |
| 237 |
Mounted |
Z |
0.830 |
0.889 |
0.949 |
jpg1,
jpg2,
jpg3,
ascii, ascii*
|
From NDC Dec-2010. *Measured warm at IAC (0.3-2.6 microns) |
| 238 |
Mounted |
BK7 |
- |
- |
- |
|
From Custom Scientific Mar-2012. |
| 239 |
Mounted |
KG4 |
- |
- |
- |
|
From Custom Scientific Mar-2012. |
| 240 |
Mounted |
KG2 |
- |
- |
- |
|
From Custom Scientific Jul-2012. |
- Numbers in italics are taken from the specification, while the
normal roman font numbers are the actual filters measured in NOTCam
(at T = 74 K and filters tilted by 6 degrees).
- Transmission curves in gif, jpg or png format are those provided from
the manufacturer and taken at room temperature (300 K).
- Transmission curves in PDF format are measurements made with the NOTCam
grism #1 - i.e. vacuum wavelengths at about 74 K.
Note that these calibrations
were made through the 1 mm pinhole (7.33''), which means that the transmission
curves are correspondingly smoothed. The wavelength calibration was made with
the 128 micron slit, and the data was corrected for the small offset
introduced by using the 1mm pinhole. (The magnitude and direction of these
wavelength shifts are 0.0015, 0.0019, and 0.0025 microns for the J, H and K
band regions, respectively. The PDF plots were always correct, but the ascii
files were not corrected until 02.09.2010.)
- Some filters were measured warm from 0.3 to 2.6 microns at the IAC lab
in July 2021, and the ascii files are listed above marked with an asterisk.
Curves are shown in the plots
transmission IAC measurement and
optical density IAC measurements.
Note on filters mounted in the parallel beam.
For filters in the parallel beam there will be a small shift in wavelength of the
transmission curve across the field of view of the detector. This shift depends on
the angle of incidence of the ray ( )
as a function of the radial distance from the centre of the field of view (FOV).
The angle is obtained through the relation:
= arctan (h_obj/f_coll)
where h_obj is the radial distance from the centre of the FOV in the focal
plane and f_coll is the focal length of the NOTCam collimator (165 mm). The
"edge" of the FOV of the WF camera has h_obj = 16.4 mm in the focal plane
(focal plane scale = 0.136 mm per arc second), i.e.
= 5.7 degrees at the edges. The very
corners are at h_obj = 23.1 mm, or
= 8.0 degrees. The shift in wavelength as a function of incidence angle
is calculated using:
 _
= _0 * sqrt(n² - sin²)/n
where _
is the central wavelength at incidence angle and
_0 is the central wavelength at
= 0, and n is the refractive index
of the filter. Most materials have indices that do not fall below n ~ 1.4. In the below
example we use this value, and make a worst-case-performance calculation for the WF camera
and a filter in the long wavelength (K-band) region.
Thus, for filter # 218 (lambda_central = 2.118 microns) used with the WF camera, we
get a maximum shift towards the blue of 0.005 microns at the edges and 0.010 microns
at the corners due to fact that the filters are mounted in the parallel beam.
The effect is thus negligible for broad-band filters, but of some concern for the
narrow-band filters.
Note that the central wavelengths of the filters measured at the NOT, i.e. the reference
wavelengths given with normal roman fonts and the transmission curves in PDF format in the
table above, are obtained while mounted in NOTCam and at operating temperature (T = 74 K).
Hence, wavelength shifts introduced by temperature and by the fact that the filters are
mounted tilted, are already included.
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