Asher Kelman
OPF Owner/Editor-in-Chief
Doug,Regarding the matter of using just an angled test target for AF testing, I happened to run into this from Chuck Westfall of Canon in his Tech Tips column in The Digital Journalist for December 2008:
• Do not attempt to autofocus on an angled chart, because doing so will degrade the consistency of the camera's focusing measurement. Keep in mind that the camera's AF sensor is comprised of multiple pairs of linear pixel arrays. If you attempt to autofocus on a single line in an angled focusing chart, only a few pixels from each active pixel array will "see" the target. Ideally, the contrast in the reference target should cover the entire area of the camera's center focusing point, and the reference target should be perfectly parallel to the camera's focal plane.
This is consistent with Canon recommendations I had seen in the past.
Here is the link to Chuck's column:
http://www.digitaljournalist.org/issue0812/tech-tips.html
Best regards,
Doug
This is exactly what the LensAlign™ does! The left part is the orthogonal target, obeying Canon's directive. The right part with the slanted ruler is what we look at in the photograph taken after focusing on the orthogonal target.
The latter action gives us the line of sharpest focus!
Asher