Bryan thanks for the review and the ISO charts


I am hoping thatyou can elaborate on this statement


"Less impressive is the much-hyped-by-Canon with-extender-III image quality performance. My Canon EF 400mm f/2.8 L IS USM version I Lens performed at least as well as either of my Canon EF 400mm f/2.8 L IS II USM Lens lenses with extenders mounted."


The comparison between the two seem to suggest a fair amount of improvement in the midframe.


[View:http://www.the-digital-picture.com/Reviews/ISO-12233-Sample-Crops.aspx?Lens=741&Camera=453&Sample=0&am p;FLI=2&API=4&LensComp=327&CameraComp= 453&SampleComp=0&FLIComp=4&APIComp=4]


With the promise in extenders improvement that is shown in the theoretical charts on the 500mm and 600mm, the decision to go with one lens or the other could be based on its performance using the extenders. I find the 500mm with a 2x to be unacceptable, it was my hope that the new lenses would improve on this.