How far behind the retina the image would come into focus  depends on the amount of farsightedness one has. What causes the eye to be hyperopic or farsighted? If the cornea is too flat and therefore not strong enough, or if the eye is smaller than average, the image is  going to come into focus "behind" the retina. Using the camera analogy: The optical system of the camera, our eye, is failing to make the picture come into focus on the film, our retina.