hab ich gerade gefunden
Zitat:
With an accurately calibrated camera, the target is seen at the correct position (distance) ΰ.
If the shot is taken when seen sharp at position Î', then AF-Pred value will be some negative value -n, indicating FF (Front Focus).
If the shot is taken when seen sharp at position Î'', then AF-Pred value will be some positive value +n, indicating BF (Back Focus).
Assuming that the visual screen focus (or CD-AF) is correct, we can adjust 0' (the zero of the PD-AF) by the AF corrections:
0' = 0 + AF-DebugCorr + AF-FA
We can of course use the final image (shot) for evaluation also (we need it for readout of AF-Pred in it's EXIF data anyhow). The shot is the master for accuracy as it uses the sensor.
Again for simplicity we are looking at CIF (Catch In Focus) with Manual-Focussing (MF):
A) If you turn the AF distance on the lens from shortest distance towards the target ΰ, then the AF system will enter the DOF zone from the near side i.e. the AF will release the shot at a position Î' and AF-Pred will be negative (-m). You should see a slight FF in the shot.
B) If you turn the AF distance on the lens from infinity (oo) towards the target ΰ, then the AF system will enter the DOF zone from the far side i.e. the AF will release the shot at a position Î'' and AF-Pred will be positive (+m). You should see a slight BF in the shot.
But: If you see a slight BF in case A) or a slight FF in case B) in the shots, then 0' is not adjusted correctly, which is the zero of the PD-AF (see above).
From this I conclude the rule:
If you find BF in shots with AF-Pred < 0 or FF in shots with AF-Pred > 0, then you should have a closer look at your AF-FA (or even AF-Debug Corr).
Für mich hört sich das so an, als ob der AF irgendwo packt und dann die Bewegung innerhalb des Schärfefeldes bewertet.
Das kann dann noch scharf sein oder auch unscharf, wäre dann aber eventuell eine Bewegungsunschärfe?
Sollte ein Test mit Stativ durchgeführt werden man stellt scharf, dann auf manuell und arbeitete anschließend mit der AF Feinverstellung, sollte man diese Werte verschieben können und die Annahme bestätigen
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