You might want to use Aperture Mode to get a lot of depth of field. Focus can be real tricky when shooting with big prime glass because the depth f field is so shallow.
First, you want to make sure you have set the ISO and white point for your lighting conditions. Very simple to do.
Once in aperature mode depress the shutter button halfway down and the meters appear on the screen, including the points where the exposure and focus are being measured. Turn the little wheel at your right index finger to adjust exposure and move the camera around to get the focus points where you want them.
Then fire away.
The camera has an auto-bracketing function. When this is selected the camera takes several shots while bracketing the exposure.
Once you find your sweet spot you can save the camera settings. One selection on the menu will restore the settings for the next project.
I shot some video in an unlighted house and was amazed at how good it did with exposure. It did great on rooms so dark I couldn't see in them, even in the darkest shadows under the cabinets. During that test I used full auto which set the f/stop too open and I had the focusing problem. Using aperature mode with a higher ISO eliminated this problem nicely.
I finally gave up on manual focus altogether and just use the auto-focus now. It works great, even with wide open f/stops, once you get the hang of it.
As I mentioned earlier it took me several days to learn the basics of this camera. For some solutions I watched some YouTube videos.
I would not buy this camera just for shooting stills. It's the video that gives this camera it's true value.