I believe that the F and FA have the same optics (which are very good). Your ZX-10 body can't use MTF, which is information coded on the FA chips indicating the lens's sharpest f-stop (which varies with zoom lenses). The F/FA 100 is very sharp and I wouldn't worry about MTF. The F version will focus fine on your body - automatically or manually. You will want to use manual focus for macro shots.
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