Originally posted by WheresWaldo This is one example of such poor wording that it makes the statement invalid.
So what is he trying to say here. The AF is not heuristic based, and doesn't improve or degrade the more you use it! All contrast based AF systems depend on the fact that there are differences in the contrast within the few pixels within the array otherwise they don't know what to focus on. The AF array doesn't see a selective number of pixels, it sees them all whether white or black or any shade in between. This is one of the best examples of spreading FUD that I have ever seen, maybe Doug should be in marketing!
Now I am not picking on you Jeff, and I like the idea of the LensAlign although I think its overpriced (personal opinion, YMMV). There is also another novel way of checking autofocus using Liveview here is a link:
AF Micro-Adjustment tool - Open Photography Forums Hey no problems. It's all just for informational purposes.
The Bart_van_der_Wolf interference test pattern is interesting and free....
What happens as one manually adjusts the focus is that at the exact optimal focus setting the background will change from uniform gray into larger (colored) aliased dots when viewed on the camera's LCD. The circles and cross hair will allow to acquire AF easily, and when calibration is optimal, moiré will be maximized on the camera's LCD.
A procedure that works for me:
- I switch to LifeView, which in its current implementation will only allow manual focus.
- Optimize manual focus by searching for maximum aliasing. This will only occur a best focus (and assuming a decent enough lens is used), otherwise the defocus will act as a low-pass filter and prevent the aliasing.
- Switch off LifeView, and watch the lens barrel's focus indicator for the next step.
- Use AutoFocus (single AF spot) to focus on the (laptop) LCD screen, and watch the direction of adjustment. That will show whether the current AF calibration setting will front or back-focus.
- Apply an adjustment via the camera menu, and repeat the procedure. Once the adjustment is optimal, there will be no difference between manual and auto-focus.
The flat computer screen will prevent misinterpretation of the focus distance, because the AF system cannot react to phase effects from subjects at other distances. That makes it quite easy to get repeatable results. And because the computer LCD emits light, it can be easily done indoors, at common shooting distances for the lens to be calibrated for.
For super tele lenses it is probably easier (for distance reasons) to use a Zoneplate type of chart outdoors.
Bart