The touch screen on the Olympus E-P3 enables a great user interface. As I have said before, I feel that this user interface is well done. The usual buttons for common functions are still there. But the touch screen is a significant enhancement for some important functions. One of these functions is selection of the focus point.
But first I need to point out the small icon in the lower left of the screen that determines touch screen operation; the touch screen can be disabled or set in one of two modes that effect shooting and focusing. There are actually at least 3 ways to determine the focus point, achieve focus and take a picture. The method you use is determined by the type of shooting you do.
The easiest focus mode and the one I enjoy for snapshots and other handheld shooting is what I refer to as the ‘touch screen shutter’ mode…simply touch the screen in the region of the scene where you want focus to be. A box appears around the area you touched and voila…image. To enable this you have to set the touch screen mode to . This mode has been panned because of the possibility of false firing…maybe a so called pocket shot. I have not had a problem with false firing though, I guess, since I usually store the camera in a bag between shots (I really don’t like neck straps) or it’s on a tripod.
Another, more conventional mode is using the screen to select one of 35 areas of the live view. By pushing the left button of the button wheel ([...]) a 5 x 7 grid appears over the live view; select one of the boxes, then wait a second or press OK. During shooting a faint outline of the chosen box overlays the live view so that you know where focus is. Press the shutter…picture taken. What’s so neat is how quick it is to select the focus point. I usually use this when shooting landscapes, and use either a shutter release cord on a tripod or the shutter button on top. It’s easy to compose the scene, then select the focus point and shoot away.
A third mode requires setting the touch screen to the  mode. In this mode touching the screen will not take a picture, but will instead display a green box and a scrollbar on the right of the screen. The green box can be dragged around the screen to locate the focus point and the scrollbar is used to adjust the size of the box, or the size of the focus area. Additionally, pushing the ‘magnify’ button gives a full screen view of the area inside the green box. (You may not realize but you can test the focus by partially depressing the shutter button.) You can really zoom in to a tight spot with this mode and see how well focus is being achieved. I think this mode would be ideal for macro work. But another thing it is good for is use with manual lenses, such as Zuiko OM lenses mounted on this camera; you’ll have more confidence that you’re achieving good manual focus.
Another related mode is entered by pushing the ‘magnify’ button. A green box appears of the size and location where focus will be taken; the size of the box is adjusted with the thumbwheel and the position is adjusted with the button dial. Pressing the ‘magnify’ button again enters a full screen view of the green box. Note that this mode does not actually make use of the touch screen so any mode for it could be chosen.