Diffraction

A great essay on Luminous Landscape by Nathan Myhrvold.

The full essay is here.

The quote that really explains the flip side of diffraction limitation is:

The diffraction limited aperture for 100 megapixels / 35mm full frame size is f/4.6 , 50 megapixel is f/6.4 . There are plenty of lenses where a 50 or 100 megapixel sensor will show some benefit. Indeed most macro lenses work well open. So do many super-telephotos like 300mm f/2.8 or 600mm f/4 – they are typically used wide open where there would be no problem with a 50 to 100 megapixel sensors.

We all know that lenses are, more often than not, becoming a hindrance before the physical diffraction of light, especially with wider angles of view. Most lenses get worse as you cross f/8.0 while 21 megapixels (35mm - full frame) suffers from diffraction around f/11.

So does your crystal ball look like you will have a 21ish MP camera with your wide angle set to f/11 while you have your 200-400/4.0DO HIS (dreaming) on a 50-100MP high speed camera and you just don't stop your lens down bellow f/6.4 - f/4.6?

Also remember that the 50D already has the pixel density of a 39 megapixel (35mm) full frame camera.

The only thing we know for sure is that the future will be interesting.