Invertalon wrote:
The key here is to watch if the focus scale changes.
Invertalon wrote:
Since the shift will be relative to whatever the camera is doing anyway. Just watch the focus scale with both, not relying on IQ
Just because there are focus scale changes, it does NOT mean there\'s an Auto Focus problem with field curvature. Remember, the focus scale is calibrated for the enter of the lens. The scale assumes you are using the center AF point. The lens itself has no idea which AF point you\'re actually using.
If you\'re using an outer AF point at close focusing distance -- and there\'s field curvature -- then that distance scale will NOT be telling you where the actual focal plane is. It will tell you where the focal plane of the center point would be. On a lens with field curvature, that would be behind the focal plane of an outer AF point.
Therefore, if you focus on a flat plane with center point, the scale will show you a certain distance. If you use an outer point to focus on the same plane, the distance scale is SUPPOSED to move further back if there\'s field curvature.
Invertalon wrote:
Yes, center lens performance will be best. So expect it to be softer closer to the edges. The key here is to watch if the focus scale changes. The 24-70 may not show much IQ difference like the 24L, 35L and 50L.
Just because there are focus scale changes, it does NOT mean there\'s no issue with field curvature. The focus scale is calibrated for the enter of the lens. It is assuming you are using the center AF point. The lens itself has no idea whatsoever which AF point you\'re using.
If you\'re using an outer AF point, and there\'s field curvature, then that distance scale will NOT be telling you where the actual focal plane is. It will tell you where the focal plane of the center point would be. On a lens with field curvature, that would be behind the focal plane of an outer AF point.
Apr 13, 2012 at 11:38 AM
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