So, thinking about the DO lens, Fresnel Lens is a pretty old device/concept in physics.

I am guessing that the reason why it has been used for camera lens only recenty is that the number of fresnel rings needed not to compromise image quality is quite high (you mention "zillions", Mark), ergo "difficult" to build... ?

Indeed, it is really cool that a 70-300 can be so small. It is shorter and lighter than the 24-70L .

I wonoder if the f/ (quite higher than 2.8) is also affected by the fresnel lens, and if so, how...