Recently I acquired 600/F4 IS2 version of the lens.
I'm using it on 5D Mark3 Body but getting Soft Images.
If I use the Lens on Tripod with Hood Mounted then I'm getting a shutter speed of 1/16 or 1/18 with ISO Setting as ISO400 and Aperture as 8.0 which is very slow shutter speed nd because of this images tend to get softer.
As soon as I remove the Hood, the shutter speed changes to 1/100, 1/250 like that which is good.
I tried to do some micro adjustments, and as advised by Canon Engineer, I changed the MF Adjustment to +2 to check sharpness but surprisingly the color or subject changed from Yellow to almost white.
I'm attaching some sample images. All these images are without any processing. Just converted to JPG, Resized for Display.