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01-14-2009, 04:44 AM   #46
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QuoteOriginally posted by Marc Sabatella Quote
But if the sensor is misaligned, I could easily see it throwing off those calculation such that the "usual" way of calculation how many turns of the screw to give for a given focal length, focus distance and focusing aperture might be off. In fact, I'd be *shocked* if the math happened to work out such that a single global adjustment actually fixed all lenses for all focus distances.
Just think of it this way: You can either correct a misaligned AF sensor by putting it in the right position (-> hardware fix) or by adding an offset to the focus mismatch it reports (-> software fix). If the software fix works this way (I present a simplified view on the matter, but in principle I assume this is what happens) then all the following calculations and actions happen as if the AF sensor were in the correct position.

01-14-2009, 04:50 AM   #47
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QuoteOriginally posted by Ben_Edict Quote
Because we also have really old F-lenses arround. These do sure not contain this detailed information (phase-correction), but focus just as any modern lens.
That's a very valid remark but as Marc one mentioned quite rightly is that usually there isn't a single cause for a problem. It could well be that some FF/BF problems are caused by smart lenses (why does "re-chipping" a lens would help otherwise? Or this this an operation that only helps Canikonians?) and other FF/BF problems have another cause. Not sure if anyone has ever investigated FF/BF (focus confirmation) issues with old manual lenses? Do they exhibit lens-specific behaviour as well or can they all be addressed by one body calibration?

QuoteOriginally posted by Ben_Edict Quote
I really think, the AF processing is done by the AF module on its own - at least with Pentax.
Yes, but that doesn't exclude the possibility that the AF system uses information provided by the lens.
01-14-2009, 05:37 PM   #48
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QuoteOriginally posted by Class A Quote
Just think of it this way: You can either correct a misaligned AF sensor by putting it in the right position (-> hardware fix) or by adding an offset to the focus mismatch it reports (-> software fix). If the software fix works this way (I present a simplified view on the matter, but in principle I assume this is what happens) then all the following calculations and actions happen as if the AF sensor were in the correct position.
Without knowing exactly how this works, I have no particular reason to believe the offset that would need to be added is constant across all focal lengths, focus distances, and focusing apertures. And if not, then indeed, it would require separate adjustment for each lens.
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