The specifications for the FLAMINGOS-2 image quality are 50% encircled energy (EE) within 25 μm diameter, and 80% EE within 43 μm at the detector (18 μm / pixel). Using images of a pinhole grid mask, we obtained a full-width-half-maximum (FWHM) of 0.36 arcsec across the 6 arcmin field-of-view, meeting the specifications.

Fig.: FLAMINGOS-2 measured FWHM, as a function of distance from center. Due to an optical misalignment, FLAMINGOS-2 showed increasing PSF values in 2013, and was brought back to specifications after an intervention in 2014. Horizontal lines mark the FWHM values in various observing bins (Image Quality 20 percentile = IQ20, etc.).