The third way in which framing may be accomplished is through focus. This consists of three things: 

1) What the center of focus is for the photograph. 
2) How sharply in focus that center is. 
3) How sharply in focus the rest of the photograph is. 
In almost all cases, the center of the photograph should be sharply in focus. However, there are exceptions. (As noted repeatedly above, there are exceptions to almost every rule in photography just as in any other art.) Controlling the focusing (once you’ve focused on the main subject appropriately) is mostly a matter of controlling the depth of field by setting the aperture, and controlling the motion blurring effects by setting shutter speed, although much can be done with the effects of lighting on focus, too.
Do you want your photo to be entirely crisp, clear, and in focus for all of its elements? Do you want part of it to be sharp and clear and the rest somewhat blurred, so as to direct attention more powerfully to the center? Do you want to convey speed or movement with a streaked or blurred effect of a moving object such as a leaping animal, a race car, or an airplane? Or do you want instead to capture all of the visible details of the object with perfect clarity? There is no always right answer to any of these questions! That’s what makes photography an art form. Although general tips can be given in a book like this, in the end the only way to learn it is to do it. That’s how you’ll discover what happens when you set your aperture to f4 while leaving the shutter speed automatic, or set your ISO sensitivity to 1600 and leave everything else automatic – or any of the huge number of other possibilities. The term “point of focus” means the object within a photographic composition to which the photographer means to draw the main attention. For purposes of setting focus, almost always the point of focus should be in sharp focus and definition. The remainder of the photograph raises questions about sharp versus blurry focus. (As always, there are exceptions, but in this case they are rare.)A DSLR camera often allows for setting the point of focus manually, so that it does not always have to be in the center of the frame. Many of the better and more advanced DSLR models even allow for setting multiple focal points. When you do this, the camera’s automatic focusing control takes samples from each of the focal points and processes an overall focus that will try to keep all of the focal points in sharp focus, as much as is possible given the depth of field that arises from the aperture setting. One should always use this control with discretion and artistry and not go hog-wild. Using too many focal points leaves the viewer’s eye with no place to rest and no strong point for attention. It can make a photograph seem overly busy. Another important thing to keep in mind is the relation between focal point and photo composition. If the foreground is cluttered with out of focus objects while the focal point is behind them, this can be distracting unless it is very carefully handled. The traditional focal point in the center of the frame should be the default in your mind. DSLR camera controls allow you to depart from this traditional composition, opening up extra possibilities. That’s a good thing, but it should be used judiciously and with a certain amount of caution until you feel confident about the technique. Despite what was said above, there are some circumstances when it is advantageous to use a lot of focal points, or even all of the focal points the camera offers. This would be when you are taking photos of moving objects whose motion is unpredictable, such as often occurs with sports photography or wildlife photography. It can be very difficult to keep a fast-moving creature such as a bird or a football team in a pre-defined focal point (such as the center of the frame). Using all of the focal points in such a case improves the ability to keep the object in focus by having the camera’s computer chip take care of the job for you.