The Nikon D750 has 11 autofocus points rated up to f/8. Which ones are the f/8 points?
According to Nikon D750 User’s Manual (rev. 03), there are 11 to 15 autofocus points rated up to f/8. On page 430, the manual details which points work with different lens and teleconverter combinations.
The 15 points that usually work at f/8 comprise the 3×3 square around the center point, a row of 3 points to the right of the square’s middle right point and a row of 3 points to the left of the square’s middle left point.
The 11 points that always work at f/8 are the center point, a row of 4 points to the right of the center point and a row of 4 points to the left of the center point, the point directly above the center point and the point directly below the center point.
The TC-14E series of teleconverters lose about 1 stop of light, the TC-17E II loses about 1.5 stops, and the TC-20E series lose about 2 stops.