[Shiraz (Ray)]

Stars are points of light with no size when viewed at interstellar distances and amateur apertures. Therefore, everything that results in round stars of varying size is an aberration. The main contributor to star size (and variation) is the seeing/guiding, which causes the points of light to wobble around and spread out into (not quite) 2D Gaussian structures. Bright stars look big because the stretching brings up more of the skirts of the bright star profiles. The relative "bigness" of the stars depends on the size of the star profile (atmospheric), the level of stretch and the sampling - fine sampling gives big stars.

On that basis, what should we aim for? I have been assuming that, when an image is stretched to bring out a dim target, the bright top end of the scene will be correspondingly compressed and brighter stars (whatever colour) will turn into almost fully saturated white disks with small skirts of unsaturated colour - as happened with film. However, I notice that many here use various forms of masked stretch to preserve some of the original profile and colour of the stars, while stretching the rest of the image (ie the image becomes a composite - one image for the stars and one for the rest). In the process, the stars taken on a fuzzier, softer appearance, with more colour.

My philosophy for now is to prefer relatively sharp edged stars (ie no masking during stretching) because they are much easier to distinguish from background galaxies, but there is clearly no right answer and I would really appreciate the opinions of others.