View Single Post
Old January 21st, 2008, 02:55 PM
Bart_van_der_Wolf Bart_van_der_Wolf is offline
pro member
Join Date: Jun 2006
Location: Netherlands
Posts: 4,046

Originally Posted by Wil Andrews View Post
Here's some very good news. This test with a 1MIII with the focus fix from Canon shows tack sharp auto focus with the three lenses I have with me (16-35L, 24-105L, and 70-200L). Earlier tests with other means showed some adjustment needed before the camera was sent in for repair.

Conduction the test as described produced such fantastic results ...
Hi Wil, that's great news. I can imagine the anxiety that was caused by the stupid handling of the AF crisis by Canon. And they also missed an opportunity to turn it into a great comeback. Anyway, I'm glad my test target helped you to verify that things are now the way they should have been from the start.

... that I felt a more rigorous test should be done. I devised a two step test:

Step 1: Do exactly what has been described here.

Step 2: Do not move camera.

2.1: While not in Live View, but in Auto Focus mode, manually rotate focus ring to de-focus the lens.

2.3: Press shutter half way down to actuate auto focus.

2.4 Without moving anything, enter Live View.

If the moire lines are still there, the auto focus returned the lens to tack sharp focus.

This part of the test should only be done after the user is satisfied with any adjustments made.
Correct. I've noticed some irregular AF behavior when the microadjustment is not done yet, but much less (if any) when things are perfectly adjusted.

I added this test to see if the lens motor and or auto focus circuit has any hysteresis (slop in returning to same point). I am delighted to report that all works fine.
Yes, it's a good test to let the AF approach focus from infinity and from close focus positions, and verify accurate focus with Life View.

The only question I have is that Canon recomends that the tests be made at a "distance similar to actual subject matter you shoot . . ." But the argument against that is that Canon doesn't and can't do it that way themselves in their service center.
Well, the recommendation is kind of obvious. One shouldn't test at the closest focusing distance and assume everything is fine, when infinity focus is more important for ones shooting. However, I think there is not too much difference between medium distance calibration and using the lens at other distances. Exceptions may be the super-tele lenses and Macro lenses, because their optimal performance is probably at the extreme distances they were designed for. The great thing about the AF microadjustment target is that one is required to adjust the testing distance to something that allows the moiré to be generated, and that automatically covers most lenses, with the possible exception of Macros (although my 100mm seems fine at all distances). Macros can still be tested by looking at how well they focus on the LCD's sub-pixels.

Reply With Quote