  Nowadays, astronomers perform point spread function (PSF) fitting for most
types of observational data. Interpolation of the PSF is often an intermediate
step in such algorithms. In the case of the Multi-AO Imaging Camera for Deep
Observations (MICADO) at the Extremely Large Telescope (ELT), PSF interpolation
will play a crucial role in high-precision astrometry for stellar clusters and
confirmation of the Intermediate-Mass Black Holes (IMBHs) presence. Significant
PSF variations across the field of view invalidate the approach of
deconvolution with a mean PSF or on-axis PSF. The ignoring of PSF variations
can be especially unsatisfactory in the case of Single Conjugate Adaptive
Optics (SCAO) observations, as these sophisticated and expensive systems are
designed to achieve high resolution with ground-based telescopes by correcting
for atmospheric turbulence in the direction of one reference star. In plenty of
tasks, you face the question: How can I establish the quality of PSF fitting or
interpolation? Our study aims to demonstrate the variety of PSF quality
metrics, including the problem of revealing IMBHs in stellar clusters.
