When using Sony lenses in manual focus (or DMF mode) the camera can be set to zoom in when the focus ring is turned. This works because the E-mount lenses use fly-by-wire focus so the camera knows that the focus ring has been turned.
When an old manual lens is fitted to the camera using an adaptor the camera has to be in 'no lens' mode as no information is passed from lens to camera. For a while I was relying on focus peaking to see what was in focus, then I discovered by accident that if I pressed the button adjacent to the bottom right of the rear screen it focus zooms, press it again and it zooms in further. To get back to the full view half press the shutter button.
By using this button it is possible to accurately set the focus and aperture to achieve the desired depth of focus. It is actually easier to get very accurate focus and depth of focus using a non-Sony manual lens than it is using one of the Sony lenses in manual or DMF mode, largely because you are in control of when the focus zoom is active, when using this mode with an E-mount lens the camera zooms back out after a timeout, which isn't as helpful.
Another feature of DMF is that you have to hold the shutter button half way while manual focusing. The shutter button is very sensitive and it is difficult to manually tweak the focus without either letting go or taking the picture prematurely. The principal advantage of DMF is that focus peaking is shown after auto focus which give you some idea of what it or is not in focus.
For manual focusing with an E-mount lens put the camera into manual focus mode, it is a lot easier than DMF.