Also, the screen control may affect the focus and the geometry (probably X-ray emissions as well). When adjusting the screen control, you don't want to crank it up too high. I usually set the brightness (not the screen) right about at the middle point, or just past, and adjust the screen control to give a nice, contrasty picture with good blacks. Then, try adjusting the brightness control, to make sure it has good range, and doesn't cause the image to "bloom" or lose focus.
When my RGB monitor died a while back, I pulled another one from my basement and did a quick adjustment just to get up and running. The picture was a bit fuzzy, and couldn't be sharpened fully with the focus, so I thought perhaps the monitor had more wear than the previous one. After upgrading my system, I decided to take another whack at it, and found that my screen control was not properly adjusted. It's beautiful now, with sharp, readable small text across the entire screen at 640x480i desktop resolution, bright colors and deep blacks. Be patient (and careful!), and go back and forth between the controls until you get it right. It's worth the extra time it takes.