Astrophotography diagnosis of LDN 673: Tracking drift and sensor tilt

The PSF panel is reassuring once the C cell is set aside. That zone reports FWHM 1.33/0.38 and elong 3.48 with a Moffat ellipse visibly placed on an artifact (saturated/streaked pixels, a blend), and the red reticle does not land on a clean star. As required by the safeguards, this non-conclusive measurement cannot serve as a discriminant. The automatic tracking pre-verdict and the sensor-tilt candidate rely exclusively on it, so I reject both.

The eight other zones tell the opposite story: elong from 1.04 to 1.12, all at or below a mono camera floor, with remarkably uniform FWHM (3.3 to 3.7 px) between center and corners, a corner/center ratio close to 1 once C is excluded. There is no readable diagonal asymmetry (the PAs are scattered, not aligned), hence no real tilt signature; no coherent directional elongation, hence no tracking drift. Focus is good and the EQ6-R held the 180s without flinching.

The measured background (+30% radial, R-squared 0.18) corresponds to the region's nebulosity, not vignetting. The DSS confirms a star-rich field with dark absorption, consistent with LDN 673. As it stands this is a healthy sub: the priority is simply to stack enough exposures to reveal the dark cloud and the faint IFN.