What's with those AF points on the A99? 19 cross-type, plus 102 phase-detect AF points? Firstly, I always though cross-type sensors were a type of phase-detect sensor, based on having two phase detect strips arranged in a cross. I suppose contrast-detect is cross type by default, since it's based on the orthogonal grid of the main sensor.
Looking at the press release (where that piece of text originally came from) the 102 point phase-detect points are on-sensor, which doesn't make any sense to me. Phase-detect systems rely on splitting parts of the light from different routes through the lens, checking for any phase difference from the two areas that would indicate the lens isn't focussed. The sensor gets light from all routes through the sensor, to maximise the light it can collect. It would also suggest the 19 cross-type sensors aren't on sensor, as I'd originally assumed they might be (if they were in fact contrast-detect type).
I really can't make head nor tail of this. Mind you, Sony's semi-transparent technology stuff confuses me at the best of times.
What am I missing? And where's the contrast-detect in this setup?