Comments on new review of 600mm II just posted

[Scully]

Bryan, I always appreciate your reviews and optical comparison tools. Thank you for the review of the 600mm II. I did have one comment, that I disagree it might obsolete the 800mm. If you only ever need 800mm of focal length, and no more, then I will accept your statement that the 600mm II with a 1.4x III is as sharp as the 800mm, but cheaper and lighter, and gives you a 600mm f4 as well. But for avian and wildlife photography, there is no such thing as too much focal length. I sometimes use my 800mm with a 1.4x II to give 1120mm, even with a 1.6 crop camera. Some softening due to diffraction is clearly visible, but I can achieve more resolution with this combination than by using 800mm and cropping. My point is that the 800mm + 1.4x combination has better image quality than a 600mm + 2x, hence the 800mm still plays an important role.

Of course, the 800mm can also be used with a 2x extender. But with an 18 Mpix 1.6 crop camera, the image is so soft that it gains little resolution compared to just cropping. Therefore I don't bother carrying a 2x extender anymore. But when I upgrade to a 5D III, I can probably get useful images from an 800mm + 2x combination, because the diffraction limit is higher due to the larger pixels. Again, then, the 800mm still retains an important advantage of more focal length over a 600mm + 2x.

My wildlife kit has three lenses: the 300mm f4, the 500mm f4 I and the 800mm. Each lens increases my focal length by 1.6x which I find about right. Interestingly, although your tests show that the 500mm II is sharper than the 500mm I, I don't feel any need to upgrade my 500mm I, because I never use it with a 1.4x extender. I use my 800mm instead. Therefore my 800mm allows me to get away with an older and cheaper 500mm than I might otherwise desire.

Any other comments from anyone on the new review of the 600mm II?