Just read up about the airy disk. That's quite interesting. Seeing can be such a complicated subject and so much maths is involved in astronomy. When I deal with the subject, I always try to simplify things and get away from the maths. For astrophotographers such as myself I believe we shouldn't dwell too much on all the unknowns we cannot control and I generally stay away from the maths. I'm more interested in the practicalities of improving the quality of the image with the conditions as they are.