Calibration removes everything in your frames that isn't sky signal. Bias frames (zero-length, capped) capture the electronic baseline — read-noise pattern, ADC pedestal, column banding. Dark frames (same exposure and temperature as your lights, lens capped) capture thermal current, hot pixels, and amp glow. Flat frames (evenly illuminated, ~50% histogram) map vignetting, dust shadows, and per-pixel sensitivity. The calibration math: calibrated = (light − master_dark) / normalized_flat. Bias/darks are subtracted; flats are divided. Stack many of each so calibration adds no noise of its own.