Phoenixkh wrote in post #18610067
I'll have to try that. I've never used live view with the 1D IV. For some reason, I thought its live view was pretty far away from the current designs. I used to use the live view on my 70D... hardly ever with my 7D2.
I've never used the 1D IV, but I assume it'll be using contrast AF in liveview; it's slow, but should generally be very accurate.
MFA is only to correct for differences between the lens-to-imaging-sensor vs lens-to-AF-sensor paths (when using phase AF through the viewfinder). When using liveview (even the modern dual pixel AF) the AF sensor is the imaging sensor, so if the image is in focus on the AF sensor, it's in focus on the imaging sensor (which may not be true when focusing through the viewfinder).
If things look OK with liveview, it may be an MFA issue. If not, then it may be a dodgy TC (though they will always have some hit on quality anyway).