[davidmanze]

Please remember

- on the EOS 5Ds R the practical peak resolution is around f/4. Thus the Tamron is already beyond that especially at the long end

- the MTFs decrease due to air diffusion starting to kick in at 300mm. At 600mm this costs probably "a half mark"

- of course, 600mm prime lenses will be better so it's just unrealistic to expect wonders from a lens that is this affordable

Oh F4!..  At 600mm the T is at F6.3 and just plain soft ..except close up.

 

 

JoJu's quote from lenscore shows for the 600mm F4  the difference between pro-lenses and consumer zooms.

 

 

Also I've just had the misfortune to spot a Nikon AF-S 500mm F4 on "the bon coin" site non VR, for about a grand more than the Sigma Sport,   with a converter it would give me 700mm F5.6 on FF and 1050mm on APSc, plenty enough, but, it's 4 Kgs...no doubt about the sharpness though!

 

Hmmm... BC...help me!