Originally posted by Marc Sabatella You certainly could, but that makes the results a lot harder to quantify, and still leaves a considerable amount of guesswork (just how much in front to try bracketing to avoid accidentally over-correcting etc). It's just a heck of a lot more imprecise than a test that can show you a gauge you can read clearly to see exactly how much FF or BF there is.
And yes, Jeff- sorry, I didn't check out the link. Looks like a nice device, but I guess I remain unconvinced that the angle method is that bad, since as others have mention, even if it is not an *ideal* test subject, it does mimic reality. Anyhow, I now quite convinced that the majority of reported focus problems are actually cases or poorly run tests,
I fail to see how a thin black line on a piece of paper "mimics reality"
Anyways if Canon says "no" and Doug Kerr is seemingly in agreement, that's good enough for me............
THESE ARE QUOTES!
Originally Posted by Doug_Kerr View Post
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/iss...tech-tips.html
Best regards,
Doug
AND...........
Here are a few additional precautions to observe:
• 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.
• For best results, manually set the focus on the lens to infinity for every exposure before allowing the camera to autofocus the reference target.
• Expect some minor variations in focusing accuracy within each set of three test images, even though they were all taken at the same microadjustment setting. This is completely normal, and is due to the tolerances of the camera's AF system.
• Expect smaller microadjustment settings to have a greater effect with telephoto lenses, and vice versa for wide-angle lenses.
• If you are attempting to set microadjustments for a zoom lens, it is important to realize that the camera's setting may only be accurate for the focal length setting you test. The instruction book suggests testing at the longest focal length of the lens, but you may find it more efficient to choose the focal length you use most often.
• Some EOS cameras and some EF zoom lenses may require more sophisticated calibration than the in-camera AF microadjustment settings can provide. In such cases, it may be necessary to have calibrations performed at a Canon Factory Service Center.
• Last but not least, there is no "official" Canon method for setting AF microadjustments, so this procedure is unofficial. If you think you can do better, then by all means, go for it. Towards that end, be advised that some independently made tools are designed to help you set AF microadjustments accurately. One of these is the LensAlign kit, due out soon from RawWorkflow.com:
Tech Tips - The Digital Journalist