Originally Posted by wickerprints
I have to really agree with what wickerprints said here, that the 2x III is responsible for most of the performance gain, since the original 400L was an amazing lens as it was.
This example really illustrates that point:http://www.the-digital-picture.com/Reviews/ISO-12233-Sample-Crops.aspx?Lens=327&Camera=453&Sample=0&am p;FLI=2&API=4&LensComp=741&CameraComp= 453&SampleComp=0&FLIComp=2&APIComp=4
Keep in mind there's more to performance with the 2x III than just image quality. If focusing speed and tracking ability is greatly improved, I would say some of the hype about the new lenses and extenders would be justified.
I would say a lot of the value of the new 400L II is the significant weight savings and improved IS. Any improvement in image quality is just a bonus. Though maybe someday we'll see more of a difference from a higher density sensor than what is currently available. I'd actually be curious to see 100% crops from the 400L vs. 400L II on a 7D sensor, perhaps any image quality differences would be more noticeable. Think you could indulge me Bryan?