What is the effect of, and when would you use, the ‘Lens drive when AF impossible’ setting on a 7D Mark II?
Martin Peterson, York
Brian Says… This setting determines how the camera behaves when a tracked subject is no longer covered by an AF point. It’s useful for photographing birds against a plain sky background with long lenses, for example.
When you are focus-tracking a bird that moves away from the AF points, the camera normally drives the lens to move focus from infinity to minimum distance, as it searches for the subject. That makes the subject so out of focus it can be hard to find.
If you turn the function off, the camera won’t change focus, so you have a chance to locate the bird at a similar distance. You can tap the shutter button or back AF button to force the lens to restart searching.