Here is a simulation of a far-sighted eye. The
lens at the front of the eye is "too weak", and is converging
the light after the back of the eye (so, the light that gets to
the back will be out of focus - fuzzy - for close objects). To correct for
this type of vision, we put a converging lens into the eyeglasses -
conceptually, this pre-converges the light before it gets to the eye-lens,
and thus when the eye-lens converges it, it will now converge on the back
fo the eye for proper focus.
There is another interesting view of this system ... consider the nearpoints and far points of the human eye. Eyes that don't need any correction have a near point of about 25 cm, and a far point very far away (essentially infinite). Far-sighted people have a near point that is dramatically farther away (they can't see things up close) - for example, suppose it was 40 cm from the eye ... so that far-sighted eye "can't" see anything closer than about 40 cm (the distance would change depending on how far-sighted the person is). So, what is that eyeglass-converging lens doing ... look at the light coming from the eyeglass-converging lens .. what does the eye-converging lens think about that light .. it thinks it is coming from an "object" that is much farther from the eye-lens than the original object .. and if it is outside the near point .. the eye-lens can now resolve that image properly!!! That VIRTUAL IMAGE from the converging eyeglass-lens becomes a new REAL OBJECT (farther away!) to the converging eye-lens .. and thus the eye lens does what it does, and resolves that "far" object as an image on the back of the eye.
To run the physlet - when it starts, the eyeglasses are off to the left (away from the "face") - notice where the light converges .. beyond the back of the eye. Move the eyeglass-lens (the left converging lens) to the right ... past the "object" and place it where it needs to be so that the light will converge on the back of the eye. Now look at the light that comes out of the eyeglass lens, toward the eye's converging lens ... it looks like it is coming from a point much farther away to the eye than where the object really is - and, that new "object" point is outside the near point!! That's why the eye can now see the object "correctly" .. the converging eyeglass has tricked the eye into thinking the object is much further away than it appears!
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