I bought the a7ii as my first full frame camera and I'm struggling to get the IQ I want. The AF is slow and finicky, especially Eye-AF, the ISO performance is really disappointing (ISO 800+ is too noisy for my taste) and the low light focusing, well, it's just not good. Has anyone had similar problems with this camera and knows how to get the best IQ and performance out of this camera or do I have to get the more advanced a7rii or a faster DSLR?
Perfect focus in the dark can be obtained with the SharpStar2 Filter Mask: https://youtu.be/9WgCPTrCv60 .
It's a Bahtinov Mask that produces diffraction lines around a bright object (even a Star) and allows exact manual focusing. See: http://www.lonelyspeck.com/sharpstar/ .
A more expensive method with limited distance is to use a "Auto Focus Illuminator" which projects a high contrast pattern on your subject. Few Cameras have this but you can add the feature to those that don't using a Speedlight with such a feature.