Originally Posted by Yorkshiretea
Diffraction doesn't do anything to
the lens. It's a propery of
it. It's just light passing through it in a scattered manner, and at the wavelength end of things it's allowing the light waves to seperate based upon their wavelength, forming a prism. It still doesn't alter the lens's physical character, it's still the same size, shape and density, which is what controls how light behaves through a lens.
Unlike heat which does change it's size, shape, and density and thus alters how light passes through it. But more likely the expansion of items in the scope's construction just moves the parallax lens assembly a fraction of a mm and it focuses to a slightly different point.