[bird (Anthony Wesley)]

Bert, I'm not sure about this interpretation - it may be ok but I have not seen the airy disk presented this way (in 3D).

The equations I've seen for the size of the airy disk only talk about mirror diameter and the wavelength of light, not brightness. But your explanation implies that the airy disk size can be made smaller by decreasing the brightness.

e.g. in my copy of the Suiter book on star testing, he gives the formula for the size of the airy disk as:

r = 1.22Lf/D

L=wavelength, f=focal length, D=diameter of mirror or objective.

Am I interpreting your comments correctly?

regards, Bird

edit - I think I understand your comment now, are you saying that a dimmer object will have a smaller central bright spot and a larger dark gap, but the overall size of the airy disk remains constant...

Applying this idea to extended objects like planets is a bit interesting, you might divide the object into an infinite number of very dim points, leading to some odd conclusions.

Just thinking aloud here...