Summary
NASA says the Nancy Grace Roman Space Telescope’s Wide Field Instrument reached an optical error of 63 nanometers RMS after commissioning adjustments, against an image-quality requirement of about 90 nanometers RMS. The team describes the instrument’s performance as nearly 30% better than predicted.
NASA said on October 14, 2026, that its Nancy Grace Roman Space Telescope team had completed a round of checks and adjustments to prepare the observatory’s Wide Field Instrument (WFI) for routine use. After the corrections, the WFI’s optics had an error of 63 nanometers RMS, below an image-quality requirement of about 90 nanometers RMS. NASA described the instrument’s performance as nearly 30% better than the team had predicted.
Testing Roman’s wide-field camera
The WFI is central to Roman’s planned surveys. NASA says the surveys will use it to pursue mission goals that include studying dark matter and dark energy. Since activating the instrument in September, engineers have tested its components individually and together.
The checks covered 18 detectors, each about the size of a sticky note, and their electronics. Engineers also tested the element wheel, which holds filters and other tools that select wavelengths of light or separate light into colours. The instrument’s calibration system uses controllable internal LEDs to check how the detectors respond to different light levels and account for variations in sensitivity. The team also tested the alignment mechanism and the system that keeps instrument components at the proper temperatures.
RMS, or root mean square, is a way of summarising optical deviation. In this case, the 63 nm RMS result is the team’s measurement of the WFI optics after applying corrections; the approximately 90 nm RMS figure is the image-quality requirement. NASA says the WFI’s survey images should therefore be sharper than expected.
Fine adjustments to the telescope’s optics
A separate effort brought the telescope’s mirrors and other optics into closer alignment. Light entering Roman reflects between these components before reaching its instruments, so their alignment affects how sharply the telescope can focus an image. NASA said the initial performance was already strong, but small corrections were needed because conditions during launch and in space—including gravity, temperature variation and moisture—cannot be reproduced exactly in ground tests.
The team moved the secondary mirror by about one-sixteenth of the diameter of a human hair. NASA reported that the Coronagraph Instrument, which had initially been slightly out of focus, was brought into focus as well. Its team is continuing to tune the camera and deformable-mirror settings before attempting a demonstration of its light-blocking capability in the coming weeks. That demonstration is a separate next step from the WFI’s reported image-quality result.