Characterizing Drift-Limited Performance in Unguided Astrophotography with Large-Aperture Newtonian Telescopes

This technical note evaluates the observational performance limits of unguided smartphone-based astrophotography using a large-aperture Newtonian telescope under low-latitude sky conditions. Observations were conducted with a consumer-grade 10-inch Newtonian reflector coupled to an iPhone 15 Pro Max mounted on a manual altazimuth system, without motorized tracking, under semi-urban skies in Planeta Rica, Colombia (8.4° N). Image acquisition employed 5 s exposures in night mode combined with real-time manual drift correction. Under these conditions, resolved stellar and nebular structures were obtained for the Orion Nebula (M42) and the open clusters Messier 44 and Messier 41, reaching a limiting magnitude of approximately 9.5 while maintaining stellar elongation below ~1–1.3 arcminutes, consistent with the expected sidereal drift during a 5 s exposure. Lunar imaging achieved high spatial fidelity, resolving terminator features such as Tycho and Mare Imbrium with negligible motion artifacts. Imaging of Sirius (–1.46 mag) revealed pronounced sensor saturation and blooming, highlighting dynamic range limitations inherent to smartphone detectors. Quantitative analysis indicates that active manual correction reduced positional drift by approximately 52% relative to theoretical unguided motion models. The results demonstrate that optimized acquisition protocols enable reproducible and methodologically interpretable imaging of bright astronomical targets at equatorial latitudes, providing a practical framework for characterizing the constraints of unguided smartphone astrophotography.