Sony Alpha and NEX cameras have two very nice features that make manual focusing a pretty effortless exercise. The first one is focus peeking, where the areas in focus are highlighted in a selected colour, and the other one is manual focus assist (MF assist).
The way MF assist works is that when the camera is in MF mode, the preview screen on the LCD display or EVF is magnified, making it very easy to see when the subject is in focus. Once the MF assist is enabled, all you need to do is to turn the manual focus ring on your lens and the magnification kicks in.
However, if you are using third party lenses with the lens adapter in manual focus mode, the screen magnification doesn’t work. You can turn the focusing ring all day long, you will only have the benefit of focus peeking but not the MF assist.
was made for the E-mount APS-C range of cameras, e.g. NEX-6, 
etc. Normally, using this type of a lens on the full frame cameras, such as A7, would cause a very heavy vignetting where the image, unless seriously cropped, would be pretty much useless.
on the full frame camera.