In the previous lesson, Vision, we studied how the eye “sees”, and how the lens of the eye changes its thinkness to focus on nearby and faraway objects. But how does the thickness of lens affect focus? To understand that, we need to study Newton’s optics. When light passes through substances of different density or thickness, it “bends” or refracts. Essentially, the shape of the medium affects how light is “bent” or refracted through it.
In the preceding figure, the light hitting a specific point in the object refracts as it passes through the lens. Notice how the angle the light is deflected is greater at the edges and become progressively less towers the middle. Also, when light passes through lens shaped like the lens of the eye (called a convex lens), the image formed is inverted. So how come we don’t “see” things inverted? Well, the brain knows that the image is inverted and corrects the interpretation.
In cameras, the lens is moved forward or backward, is small increments, to make the object come into focus. The principle is the same when you’re using a magnifying glass. You move the lens either closer or farther from the object while your eye position remains constant, to bring the object into focus, right? The inverse is also true: holding the magnifying glass stationary, you have to move your eye (yourself included, of course) closer or farther from the magnifying lens to bring the object into proper focus. Of course, the farther the lens is from the object, the larger we see or perceive it to be.
Next Lesson: Focal Length