Appendix: Available Optical Path Difference (OPD) files

For each of the five instruments (four SIs plus FGS) there are three provided OPD files. These represent wavefronts as follows:

  1. The OTE and ISIM intrinsic WFE
  2. The above, plus a slight defocus to blur the image slightly to approximate image motion.
  3. The above #2, plus additional WFE due to SI internal optics.

The latter is the largest WFE, and is the default file used in simulations unless another is explicitly chosen. For NIRCam only there is a second, duplicate set of these files with slightly improved WFE based on an optimistic case scenario for instrument and telescope alignment.

The provided OPDs are based on the observatory design requirements, and were developed for the Mission Critical Design Review. The represent the nominal case of performance for JWST, and have not yet been updated with as-built details of mirror surface figures, etc. We intend to make updated OPD files available once suitable reference data have been provided to STScI. For now, see Lightsey et al. 2014 for recent predictions of JWST’s likely performance

Note that the trick of adding some (nonphysical) defocus to blur out the PSF is computationally easy and rapid, but does not give a high fidelity representation of the true impact of image jitter. This is particularly true for coronagraphic observations. Future versions of WebbPSF will likely provide higher fidelity jitter models.

The units of the supplied OPD files are wavefront error in microns.

Rev V OPDs
File Instrument RMS WFE Includes OTE + ISIM OPD? Image motion (as defocus)? SI OPD?
OPD_RevV_fgs_150.fits FGS 150.0 Yes No No
OPD_RevV_fgs_163.fits FGS 163.0 Yes Yes No
OPD_RevV_fgs_186.fits FGS 186.0 Yes Yes Yes
OPD_RevV_miri_204.fits MIRI 204.0 Yes No No
OPD_RevV_miri_220.fits MIRI 220.0 Yes Yes No
OPD_RevV_miri_421.fits MIRI 421.0 Yes Yes Yes
OPD_RevV_nircam_115.fits NIRCam 115.0 Yes, optimistic case No No
OPD_RevV_nircam_123.fits NIRCam 123.0 Yes No No
OPD_RevV_nircam_132.fits NIRCam 132.0 Yes, optimistic case Yes No
OPD_RevV_nircam_136.fits NIRCam 136.0 Yes Yes No
OPD_RevV_nircam_150.fits NIRCam 150.0 Yes, optimistic case Yes Yes
OPD_RevV_nircam_155.fits NIRCam 155.0 Yes Yes Yes
OPD_RevV_nirspec_125.fits NIRSpec 125.0 Yes No No
OPD_RevV_nirspec_145.fits NIRSpec 145.0 Yes Yes No
OPD_RevV_nirspec_238.fits NIRSpec 238.0 Yes Yes Yes
OPD_RevV_niriss_144.fits NIRISS 144.0 Yes No No
OPD_RevV_niriss_162.fits NIRISS 162.0 Yes Yes No
OPD_RevV_niriss_180.fits NIRISS 180.0 Yes Yes Yes