Point source

[John in Penzance]

I've reached De-convolution (at Steve Richards' Making Every Photon Count Third ed. p122) and I have a question.

For a point source, regardless of brightness, the Airy disk and diffraction circles will cover the same area of the camera sensor. The seeing will smear this over the same extended area of the camera sensor regardless of brightness.

So does a bright star appear fatter than a dim star in an image because more diffraction circles register on more and more distant pixels? Or is there another reason I've not grasped? It's the fatness of the star image that's bothering me, not how bright it appears on the image.

Is a fatter star on a captured image an accurate reflection of the real sky's brighter star, or is it an artifact of the imaging system?

[andrew s]

44 minutes ago, John in Penzance said:

a bright star appear fatter than a dim star in an image because more diffraction circles register on more and more distant pixels

This is basically correct provided you are not in the read noise or saturating the sensor.

Regards Andrew