On October 14, 2026, NASA reported that the Nancy Grace Roman Space Telescope’s Wide Field Instrument (WFI) reached 63 nanometers RMS of optical error after corrections, against an image-quality requirement of about 90 nanometers RMS. The gap is 27 nanometers, or 30% of the reference value, so NASA’s percentage describes a reduction in reported optical error. NASA’s commissioning update says Roman’s survey images are expected to be sharper than planned, while the 30% figure itself is the error comparison.
What the WFI’s 30% result measures
RMS, or root mean square, is the measure used for the WFI’s optical error. NASA’s two reported figures are:
| WFI measurement | Optical error |
| Image-quality requirement | About 90 nm RMS |
| After optical corrections | 63 nm RMS |
The calculation is (90 − 63) ÷ 90 = 30%. It compares the reported error with the requirement; NASA also expects sharper survey images, but describes that expected sharpness separately from the percentage.
How NASA brought the WFI into focus
NASA said the WFI was activated in September 2026, after Roman launched on August 30. The commissioning checks covered its 18 detectors, detector electronics, element wheel, internal calibration LEDs, alignment mechanism and thermal control. NASA described the work as preparation for routine use.
The WFI’s alignment mechanism had been stowed out of focus for launch. During commissioning, the team moved it to its predicted best-focus position and made small optical adjustments. NASA optical engineer Alden Jurling said the secondary mirror moved about one-sixteenth of the diameter of a human hair. Roman optical systems lead Matthew Bolcar explained that ground testing could not exactly reproduce conditions in space, including weightlessness. NASA credited pre-launch testing and modeling at NASA Goddard Space Flight Center, L3Harris and BAE Space and Mission Systems as part of the preparation for those on-orbit corrections.
The Coronagraph Instrument had a separate focus check
NASA reported that Roman’s Coronagraph Instrument (CGI), a separate instrument from the WFI, initially produced slightly out-of-focus images. The team corrected the focus, and CGI’s performance met its expectations. NASA’s October 14 account said the team planned a demonstration of the instrument’s light-blocking capability for the coming weeks.
