I think I shared that link (that site has great tutorials, all of them!)
Diffraction doesn´t depend on the lens. Interaction of light with the sensor, the lens just provides more or less light but the f-stop is meant to keep that ammount of light equivalent for every focal length so it is not important. Now, if you take "étendue" into account, then FL does play but that´s a different topic.. Great read on that:
Clarkvision.com: Low Light Photography: When f/ratio Does not Tell the Whole Story
If you click "show advanced" on the cambridge Diffraction Limit Calculator, you´ll see the parameters involved in diffraction but, how much of each do you nide to make diffraction
visible? Complete the chart and write down some numbers.
Ron, what are your typical printing sizes and viewing distance? These two will determine what´s is in acceptable focus and what´s not (this is called CoC = Circle of Confusion). The CoC is what also define your DoF = Depth of field, of course... which you control with the lens aperture. And aperture also defines the "airy disk" which is the minimum area of detail an aperture value allows to be resolved (relative to a given pixel size). So there´s a trade off between what´s in focus (CoC) and how big the Airy Disk gets (bigger, less detail) and both are controled with the aperture value!
As long as the CoC (what´s considered in focus) is bigger than the airy disk, you´ll be safe from diffraction.
So, you want to shoot a hockey player with your new K-3, before clicking you think "I´d like to do a 20x30cm ( print and see it at reding distance = 25cm). You may close down to f/16 without any problem.
"Ok great" let´s make a 40x60cm print and view it at 25cm too, what happens then?" Well, then try not go further than f/11 to keep good detail.
That helps?