Majority of the comments mentioned flats correct for vignetting and dust, however there is more:
- Correcting for Vignetting: Vignetting refers to the darkening of the corners or edges of an image caused by light falloff in the optical system. Flat frames capture the evenly illuminated sky or a light source, allowing you to measure and correct for the vignetting effect. By applying the calibration information from flat frames, the uneven illumination across the image can be normalized, resulting in a more uniform background.
- Dust and Debris Removal: Flat frames also help in identifying and removing dust particles, smudges, and other debris present on the camera sensor or optical elements. These imperfections can cast shadows or create dark spots in the images. By capturing a flat frame with the same exposure settings as the light frames but with the telescope or camera lens capped, the imperfections become visible as dark spots. These spots can then be subtracted from the light frames during the calibration process.
- Sensitivity Variations: Camera sensors often have variations in sensitivity across the image area, resulting in different levels of brightness. Flat frames allow you to measure these variations and apply corrections to compensate for the sensor's non-uniform response. This ensures that the final image accurately represents the true brightness and colors of the celestial objects being captured.
- Optical Imperfections: Even high-quality optics can introduce subtle imperfections like diffraction patterns or ghosting. Flat frames help in identifying these imperfections by capturing the uniform illumination of the sky or a light source. They provide a reference frame to measure and correct for any optical artifacts that may affect the final image quality.
Here are a few reputable sources that discuss the significance of flat frames in astrophotography:
- "The Astrophotography Manual" by Chris Woodhouse: This book covers various aspects of astrophotography and provides guidance on image calibration techniques, including the use of flat frames.
- "Deep-Sky Astrophotography" by Jerry Lodriguss: This comprehensive guide explores the techniques and processes involved in deep-sky astrophotography, including a section on image calibration that emphasizes the importance of flat frames.
Answer generated using ChatGPT.
If your workflow (hardware+software) doesn't experience or doesn't depend on the highlighted issues, if you like the results your workflow produces then you probably don't need flats. Otherwise, consider using them.