Astrophotography diagnosis of M45: Tracking drift, backfocus error and 1 other

The image is broadly successful: M45's reflection nebulosity is well rendered, with contrasted filaments and wisps, and a background coherent with real structure (confirmed as object by measurement, not a gradient). On the stellar side, the PSF panel shows tight FWHM (1.8 to 2.4 px) and well-fitted Moffat ellipses, so optics and focus are healthy.

Two minor signatures do measure, however. First, slight tracking drift: central elongation (1.16) exceeds the field floor with a highly coherent direction (PA dispersion of only 12°), which rules out simple native roundness and points to guiding. Second, a symmetric FWHM rise toward the four corners (ratio 1.254, center minimum), an oval profile typical of a small backfocus error or residual field curvature, right at the detection threshold.

Finally, the cores of the bright stars, including the central star, are clipped to white by the stretch. All of this remains refinement: the image is usable and pleasing, gains will come from slightly tighter guiding, fine backfocus tuning and better highlight preservation.