Starguide - A Practical Guide to Astro-Photography

Using the "Focus" docking module, adjust the "Minimum Star Size" field. This number is representative of the minimum diameter required in order to qualify as a star. If it's too low, you might pick up non-star objects... to high, you will miss a lot of valuable star data and also start picking up large parts of nebulae as false stars. Adjusting this value will adjust the number of stars detected in real time. Keep in mind that this value is representative of the minimum diameter (in pixels) at 1x1 binning and will auto-adjust when you use a binning that is not 1x1.

For example, if you set this value to 10 pixels and take your AF frames at 2x2 binning, your minimum star size is automatically adjusted to be 5 pixels. Adjust this value as low as you can without reducing the minimum diameter to less than 2 pixels after binning division occurs. For instance, if you set this value to 2 pixels, the 2x2 value will be 1 pixel and will just be auto adjusted to back up to 2 pixels to avoid inclusion of noise and hot pixels. 

If lots of diameters look good, go head and choose a "Minimum star size" (diameter) of six pixels.

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