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Which one is the best 50 mm AI (or AIS)?


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I wasn't suggesting counting whole turns only, and the lens has to remember nothing except a turns-to-distance ratio that it can pass on to the camera. And if the focus mechanism isn't made precise enough for reporting distance to a better precision than a crude gray-scale 'ruler', then it has no business being part of the AF system.

 

Oh, yeah. I forgot there's also the fact that "turns" will not be linearly proportional to distance. The first turn may pull focus from infinity down to 5 feet, and the second turn, from 5 feet to 3 feet or whatever. So if you're counting units of screw rotation (be they whole turns, or 1/16 turns, or degrees, or radians, or whatever), the lens has to know how much change in focal distance each unit of rotation away from zero represents. And yes, the lens does have to remember which "turn" it was on before the present AF movement, in order to know how many turns away from zero it is now.

 

Nikon's engineers will have considered all of this and much more before settling on the actual system of brushes and contact patches as a near-optimal solution. They're not the only vendor to have done so either.

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Nikon's engineers will have considered all of this and much more before settling on the actual system of brushes and contact patches as a near-optimal solution.

I think you give them far too much credit. Nikon never seem to give software solutions a high priority when a costly hardware solution can be put to a less effective use.

 

Counting the steps and direction of a stepper-motor is a trivial feat. As is converting those steps to real distance via an LUT or gamma factored multiplication.

 

The use of a gray-encoding strip is forgivable and cost effective for the translation of a manually positioned zoom ring. Not so for a lens controlled and focused by the camera itself. So the distance information isn't available or recorded in manual focus. Big deal.

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