Appendix: Instrument Property References

We give here references for the instrumental properties assumed in PSF computations, with particular attention to coronagraphic optics. It also notes several places where the current models or available files are limited in some manner that might be improved in a future release.

Instrument pixel scales are all based on average best estimate scales available in April 2016, specifically from values in the Science Instruments Aperture File (SIAF) data, as provided by the various instrument teams to the Telescope group via the SIAF Working Group. For instruments with multiple detectors, the values provided are averaged over the relevant detectors. WebbPSF calculates PSFs on an isotropic pixel grid (i.e. square pixels), but at high precision the SI pixel scales can differ between the X and Y axes by between 0.5% (for NIRCam) up to 2.5% (for FGS). WebbPSF also does not model any of the measured distortions within the instruments.

WebbPSF does not include any absolute throughput information for any SIs, only the relative weighting for different wavelengths in a broadband calculation. See the note on PSF normalization for further discussion.

Note: The WebbPSF software and all of its associated data files are entirely ITAR-free.


The supplied OPDs are the Mission CDR OPD simulation set, produced in March 2010 by Ball Aerospace staff (Paul Lightsey et al.) via the IPAM optical model using Zernike WFE coefficients consistent with Revision V of the JWST optical error budget.

Note: The provided files included no header metadata, and in particular no pixel scale, so one was assumed based on the apparent pupil diameter in the files. The estimated uncertainty in this scale is 1 part in 1000, so users concerned with measurements of PSF FWHMs etc at that level should be cautious.

The current model pixel scale, roughly 6 mm/pixel, is too coarse to resolve well the edge roll-off around the border of each segment. We make no attempt to include such effects here at this time. An independent study using much more finely sampled pupils has shown that the effect of segment edge roll-off is to scatter ~2% of the light from the PSF core out to large radii, primarily in the form of increased intensity along the diffraction spikes (Soummer et al. 2009, Technical Report JWST-STScI-001755)


NIRCam focal plane scale: 0.0311 +- 0.0002 (short wave), 0.0630 +- 0.0002 (long wave). SOC PRD SIAF PRDDEVSOC-D-012, 2016 April

The coronagraph optics models are based on the NIRCam instrument team’s series of SPIE papers describing the coronagraph designs and flight hardware. (Krist et al. 2007, 2009, 2010 Proc. SPIE), as clarified through cross checks with information provided by the NIRCam instrument team (Krist, private communication 2011). Currently, the models include only the 5 arcsec square ND acquisition boxes and not the second set of 2 arcsec squares.

Weak lenses: The lenses are nominally +- 8 and +4 waves at 2.14 microns. The as built defocus values are as follows based on component testing: 7.76198, -7.74260, 3.90240.


NIRspec field of view rotation: 138.4 degrees (average over both detectors). SOC PRD SIAF PRDDEVSOC-D-012, 2016 April

NIRSpec pixel scale 0.1043 +- 0.001 arcsec/pixel. SOC PRD SIAF PRDDEVSOC-D-012, 2016 April

NIRSpec internal pupil at the grating wheel: based on size of grating stop in Zemax file as analyzed and back projected onto the primary mirror by Erin Elliott, private communication 2013.


NIRISS focal plane scale, 0.0656 +- 0.0005 arcsec/pix: SOC PRD SIAF PRDDEVSOC-D-012, 2016 April

Occulting spots: Assumed to be perfect circles with diameters 0.58, 0.75, 1.5, and 2.0 arcsec. Doyon et al. 2010 SPIE 7731. While these are not likely to see much (any?) use with NIRISS, they are indeed still present in the pickoff mirror hardware, so we retain the ability to simulate them.

NIRISS internal pupils: The regular imaging mode internal pupil stop is a 4% oversized tricontagon (with sharp corners). See Doyon et al. Proc SPIE 2012 Figure 2. The CLEARP pupil has an oversized central obscuration plus 3 support vanes. Details based on NIRISS design drawing 196847Rev0.pdf “Modified Calibration Optic Holder” provided by Loic Albert. NRM occulter mask: digital file provided by Anand Sivaramakrishnan. GR700XD mask design details provided by Loic Albert.


MIRIM focal plane scale, 0.1110 +- 0.001 arcsec/pix: SOC PRD SIAF PRDDEVSOC-D-012, 2016 April

MIRIM field of view rotation, 5.0152 degrees: SOC PRD SIAF PRDDEVSOC-D-012, 2016 April

Coronagraph pupils rotated to match, 4.56 degrees: MIRI-DD-00001-AEU

Coronagraphic FOVs, 30.0 arcsec for Lyot, 24.0x23.8 arcsec for FQPMs: MIRI-DD-00001-AEU 2.2.1

Lyot coronagraph occulting spot diameter, 4.25 arcsec:

Lyot coronagraph support bar width, 0.46 mm = 0.722 arcsec: Anthony Boccaletti private communication December 2010 to Perrin and Hines

Lyot mask files: Anthony Boccaletti private communication to Remi Soummer

LRS slit size (4.7 x 0.51 arcsec): MIRI-TR-00001-CEA. And LRS Overview presentation by Silvia Scheithaur to MIRI team meeting May 2013.

LRS P750L prism aperture mask (3.8% oversized tricontagon): MIRI OBA Design Description, MIRI-DD-00001-AEU

MIRI imager internal pupil stop in regular imaging mode: 4% oversized tricontagon, mounted on each of the imaging filters (with smoothed corners).

Instrument + Filter Throughputs

Instrumental relative spectral responses are derived from the reference data files used by the Pandeia engine for the JWST Exposure Time Calculator, normalized to peak transmission=1.0 (because absolute throughput is not relevant for PSF calculations).

For the following filters we take information from alternate sources other than the CDBS:

Instrument    Filter         Source
-----------  -------------   ----------------------------------------------------------------------------------------------------------
NIRCam       F150W2          Top-hat function based on filter properties list at
NIRCam       F322W2          Top-hat function based on filter properties list at
NIRSpec      F115W           Assumed to be identical to the NIRCam one
NIRSpec      F140X           NIRSpec "BBA" transmission curve traced from NIRSpec GWA FWA Assembly Report, NIRS-ZEO-RO-0051, section 6.3.2
MIRI         F*W filters     Data published in Glasse et al. 2015 PASP Vol 127 No. 953, p. 688 Fig 2
MIRI         F*C filters     Data published in Bouchet et al. 2015 PASP Vol 127 No. 953, p. 612 Fig 3
NIRISS       all filters     Measurement data provided by Loic Albert of the NIRISS team
FGS          none            Assumed top-hat function based on detector cut-on and cut-off wavelengths.

The MIRI wide filters (F*W) are total system photon conversion efficiencies including filter, telescope, instrument, and detector throughputs, normalized to unity. The MIRI coronagraphic filters are just the filters themselves, but the detector and optics throughputs are relatively flat with wavelength compared to the narrow coronagraphic filters. These are sufficiently accurate for typical coronagraphic modeling but be aware of that caveat if attempting precise photometric calculations.

For the NIRCam and NIRSpec filters called out in the table above, the provided throughputs do not include the detector QE or OTE/SI optics throughputs versus wavelength.

All other filters do include these effects, to the extent that they are accurately captured in the Calibration Database in support of the ETCs.