I think you're conflating the sensor read speed which has been reported as 4.2ms for the Z9 and sets limits on things like flash synch speed and the need for a mechanical shutter with sensor read rate which is how many times per second a complete image can be transferred off the sensor to the EVF or the AF processing module. They're related but different measures of a sensor's performance.There are a few things that don’t compute in those statements. First, how does one get ES flash sync of 1/200 with a sensor that reads in 1/120s? i may be misunderstanding how flash sync speed works without amechanical shutter but that doesn’t seem possible. So both A1 and Z9 should have sensor read speeds faster than 1/200s which negates the fact that 120 AF calculations is just the sensor read speed.
EDIT: dpreview pegs the z9 sensor read speed at 1/270s so AF calculations run at about half the sensor read speed.
The second thing is whether the z6/7 even reach 60Hz read speeds. That’s the published number for the canon R5 and the Z7ii at least has more rolling shutter effect than the R5 which would indicate a slower sensor. The z6 on the other hand might read at that speed.
i‘LL have to see what I can find but some of those numbers don’t add up.
IOW, the 4.2ms states how fast a single image can be transferred from the sensor to processing or to the EVF, the 120Hz frame read rate tells how many complete images can be transferred per second and among other things that dictates how many times per second the AF sensor data can be transferred to the Expeed 7 processor so that can perform AF calculations. Yes, the latter (frame refresh rate) has to be slower than the limiting single frame read speed.
This information is still trickling out of different sources, much of it may be incorrect at this point, and we'll likely learn more with time. But when a simple statement like 'The Z9 performs 120 AF calculations per second' is thrown out there it's subject to interpretation. I mean after all any of these modern cameras are likely performing millions of AF calculations per second if you're talking about what's happening in the code but it seems clear to me they're talking about how frequently AF sensor data is fed to the AF processing engine(the AF system sample rate) and that's limited by the max sensor frame rate that's been published as 120 FPS for the Z9.
Sure, I'm reading a lot into very little info at this point and like all this Z9 speculation stuff I could be dead wrong and have completely misinterpreted that statement but to me it seems clear that what they meant by that claim is new data from the AF points on the sensor are fed to the AF processing engine 120 times per second.
Like all things Z9, we'll learn more when units get out into the world for hands on testing. Perhaps I've got this all wrong, we'll see...
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