The same is not always true if you use the optical viewfinder. On many digital cameras, the image in the viewfinder is usually smaller than the actual photograph, meaning that the photograph will capture more image than the viewfinder shows. Even at 200 pixels in width, the inscriptions can still be read in this thumbnail image. Click image to enlarge. Don't worry about focusing the image.
All digital cameras have auto-focus.
Just make sure the inscriptions fit inside the LCD monitor. Some tombstones are so big or so long that you have to zoom out to capture all the inscriptions. As a result, the inscriptions become too small to read. You may have to photograph pieces of the tombstone to capture the complete inscription. I've found that it helps to photograph the tombstone at an angle so as to capture more shadow within the inscription.