microadjustment not needed on mirrorless cameras, so that means...

I read that there is no micro adjustment feature on mirrorless cameras because it is not needed; so that means the third party lenses like the sigma non art series will focus perfectly when used on the sony a7 series camera? Is this a correct statement? Can anyone confirm?

The idea is that with DSLR cameras, focusing is done with the mirror and a dedicated focusing system off the sensor. This can introduce errors.

With mirrorless cameras, of any brand, the focusing is done on the sensor so the sensor should know if it has achieved the best focus. This also works with live view and DPAF on Canon.

In theory yeah, it should work with any brand lens. Not sure we can say perfectly all the time, with every combo, in every lighting condition.

THis is a really nice picture clearly showing the three different light paths in a SLR camera. A difference in light path length of even fractions of a mm will result in different results. A mirrorless only has one light path going directly to the image sensor. So, the same light path used for focus also exposes the image.