Calibration frames help correct sensor noise, dust spots, and vignetting that vary across red, green, and blue filters. Capturing darks, flats, and bias frames separately for each filter ensures each color channel is clean and consistent.
Skipping this step can cause color artifacts and uneven illumination in your final composite. Most astrophotography stacking software supports applying these calibration frames per filter, so take the time to gather good calibration data during your imaging session.
