Originally Posted by
Gray Fox
Following up on the above relative to the 1DX AF system and Canon’s lockout of AF with f8 lenses (due presumably to less reliable performance), might there be other factors in addition to the size of the aperture masks in that particular AF sensor? I’m referring specifically to the fact that the 1DX (and 5DIII) AF sensor system has cross-type sensor elements rather far out toward the edges of the sensor array, as well as a wider array than previous 1D series cameras. One explanation given for Canon’s locking out AF at f8, seen on a B&H promotional video, was that Canon “spread out the light” coming to the AF array in order to enable more cross-type sensor elements out toward the edge of the array, leaving less for reliable focusing at f8. This was stated by a non-technical representative and might have been marketing gibberish. But it does lead one to ask if and how Canon might have manipulated the light impinging on the AF sensor.
Something is certainly different technically. The 1DX and D4 arrays are roughly of equal width and height, although the 1DX has a slightly higher density of elements in the central column. But, the Nikon D4 has several sensor elements that AF at f8, including a central cross-type element. However, only the sensor elements in the central section of the D4 operate as cross-type sensors at f5.6 and wider apertures. This concentration of cross-type sensing elements in the center of the D4 array contrasts markedly from the Canon implementation, and it does make one want to know more about differences in the way light is handled by the two sensor systems.