Here is a simulation of a **telescope**. The light from the *distant
object* on the left side comes into the Objective lens (the left lens)
and forms a real image {image 1}. The second lens is called the EYEPIECE
lens, and is positioned so that the first real image forms at the focal
length of the eyepiece lens (this model shows it forming just inside the
focal length so that you can see how the image forms). The first real
image becomes a real object for the second lens, at the focal length, thus
forms a final virtual image {image 2} essentially at infinity. [As the "parallel"
rays come into the eye, from the image at infinity, they will converge to
form an image on the retina, thus you resolve the image.] You can slide
the eyepiece lens toward the left to illustrate adjusting the focus of the
telescope. For example : if the original object is very far away, the
first real image will form close to the focal length (and you would need
to move the eyepiece lens closer to the other lens). If the original
object is a little closer, then the first real image would form a little
farther away from the focal point .. thus you would need to move the
eyepiece lens away from the objective lens, so that the first real image
can be at the focal point of the eyepiece lens.
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