1DMKIII with a 300mm f2.8LIS set to f2.8 wide open at just over 2.5M away centre focus point to get focus.
1DMKIII with a 300mm f2.8LIS with a 2xII and a 1.4xII wide open 840mm at just over 2.5M away centre focus point to get focus.
I used an A4 sheet printed with an array of rulers taken from