The Synth module generates physically correct diffraction and diffusion of point lights (such as stars) in your image, based on a virtual telescope model.
Besides correcting and enhancing the appearance of point lights (such as stars), the Synth module may even be 'abused' for aesthetic purposes to endow stars with diffraction spikes where they originally had none.
Any other tools on the market today simply approximate the visual likeness of such star spikes and 'paint' them on. However the Synth module can physically model and emulate most real optical systems and configurations to obtain a desired result.
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A very popular, comprehensive tutorial titled "Processing a (noisy) DSLR image stack with StarTools" by Astro Blog Delta.
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