Fonctionnement de l'IS et collimateur actif.

[kamioon]

Dans le document Canon << Getting the most from your EOS-1 class digital SLR>>
Page 11, Autofocusing Techniques : Off-Center Focusing Points vs. “Focus Lock and Recompose”

However, many photographers never use the off-center focusing points, preferring the old-fashioned method of locking focus with the center point and then recomposing for the actual image. Before multi-point AF cameras were available, “Focus Lock and Recompose” (FLR) or manual focus were the only choices available. That’s no longer the case.

FLR is sufficiently accurate for photographing distant subjects, but it can cause focusing errors, especially backfocus, when photographing subjects within about 15 feet of the camera. This is often the case during portraiture. For optimum focusing performance with close subjects, we recommend avoiding the FLR technique. Instead, use an offcenter focusing point or focus manually.

Cela a bien à voir avec le plan focal mais c'est de la faute de Pythagore !

La map se fait en A avant la rotation du plan focal.
Après rotation, la mise au point est en B mais le point A n'est plus dans le plan focal.
L'erreur de focus est sensible sur une distances faible, à grande ouverture et avec grande rotation angulaire.

Et si Canon le dit...