This topic is in the "observing" forum, but it might be better in the astrophotography forum.
I do a fair amount of imaging.
Brighter stars tend to saturate the pixels.
Each photon when it hits the silicon ccd is converted to an electron that gets stored in a capacitor until the exposure is completed. At the end of the exposure, the camera measures the voltage to determine the brightness.
For bright stars, often the capacitor is overwhelmed and cannot collect more photons -- saturation.
My friend who does astrophotography had basically the same question as you.
He took one of his images.
He looked at non-saturated bright stars and very dim stars -- dim stars you can barely see in the photo.
He graphed the pixel value across the stars.
He got the same Airy disk profile in width for all his stars -- height varied.
He even graphed out slight bumps for the rings even on the dim stars.
We don't visually see the stars in astrophotography pics as the same size, but the computer pixel value shows the stars to be all the same width -- the computer sees the same size.
Edited by ks__observer, 21 May 2019 - 04:06 AM.