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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 Mounted J (spare) 1.167 1.250 1.334 gif,ascii Mounted in the stop wheel
203 Mounted H 1.484 . 1.780 gif,ascii NOTCam standard H
204 Mounted H (spare) 1.487 1.626 1.766 gif,ascii Mounted in the stop wheel
205 Mounted K' 1.950 . 2.290 gif,ascii
 
206 Mounted K' (spare) 1.950 2.115 2.280 gif,ascii Mounted in the stop wheel
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 ps,ascii
 
210 Mounted K continuum 2.251 2.267 2.284 ps,ascii
 
211 Mounted H continuum 1.562 1.574 1.586 ps,ascii
 
212 Mounted [Fe II] 1.632 1.645 1.657 ps,ascii,
 
213 Mounted He IA 1.070 1.079 1.089 png.
 
214 Mounted Pa 1.086 1.094 1.102 .
 
215 Mounted J-continuum 1.201 1.211 1.221 ps,ascii
 
216 Mounted Pa 1.277 1.287 1.296 ps,ascii
 
217 Mounted He IB 2.056 2.071 2.086 ps,ascii
 
218 Mounted H2 =1-0 S(1) 2.101 2.118 2.133 ps,ascii
 
219 Mounted He IC 2.167 2.184 2.200 ps,ascii
 
220 Mounted H2 =2-1 S(1) 2.233 2.251 2.268 ps,ascii
 
221 Mounted CO (2-0 bandhead) 2.271 2.288 2.305 ps,ascii
 
222 Mounted Yn 1.004 1.028 1.053 png Check note!
223 Mounted CH4 s 1.543 1.599 1.655 ps,ascii
 
224 Mounted CH4 l 1.624 1.680 1.736 ps,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 ps,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 ps,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 From NDC Sep-2010.
237 Mounted Z 0.830 0.889 0.949 jpg1, jpg2, jpg3, ascii From NDC Dec-2010.
238 Mounted BK7 - - - jpg, ascii From Custom Scientific Mar-2012.
239 Mounted KG4 - - - jpg, ascii From Custom Scientific Mar-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 ps 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 ps plots were always corrected, but the ascii files were not corrected until 02.09.2010.)

    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 ps format in the tables 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.


  • Back to top Last modified: 24-Jan-2013