Shocking insight: AF is not a closed feedback loop!

Started Jul 18, 2003 | Discussions thread
paulc Regular Member • Posts: 320
Re: Shocking insight: AF is not a closed feedback loop!

I do not believe your analysis is correct, as one obvious proof is that if you were right, the lens would never move the optical element, and then the camera would declare it cannot focus - yet we all know that this is happening.

I do agree with you that there is something operatiing "open loop". My belief is that Canon has relaxed the mechanical spec on the AF sensor location in the 10D, and tried to compensate for it in sw - in the processing of the phase signal from the sensor. But for this to work, this compensation must take into account focal length and aperture of the lens, and this is were the trouble starts, as not all lenses report these precisely. Maybe even the distance to the subject effects the compensation....

I would like to understand more of how the phase based AF works, to see if the AF sensor ( or the microlenses that feed it ) must be at the focal plane, or must be offset.

Paul.

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