The point where the lines come together is called the focal point. The position of the focal point varies with the shape and size of the lens. The distance between the lens and the focal point is called the focal length. Look at the diagram below. If your eye is at the focal point, the image you would see would be in focus, and it would be larger than the real object. Your eye pictures the image as if the lens wasn’t there. This is the same thing that happens any time light is refracted. Follow the lines from the focal point and extend them straight out beyond the lens as in the diagram. The larger M illustrates the image that your eyes would see. This type of lens - the double convex lens - is used in magnifying glasses. Note on the diagram that there is one place where the light ray doesn’t get refracted, and this is when it is going right through the middle of the lens.

Now look again at the previous diagram. The lens on the bottom is a diverging lens. If you have an object to the left of that lens, and your eye is on the right, the light coming from the object would be diverged as it went through the lens (FST and SFA again!). When your eye detects that light (and this will be explained later), it traces back those diverged rays to find the focal point. Follow the dotted lines on the diagram. This tends to bring far away objects into focus.