Optics model for a Spyglass or "Terrestrial" Telescope

Here is a simulation of a spyglass. An astronomical telescope will invert the final image, but for terrestrial viewing (such as is needed by ships on the ocean), you need an upright final image (but magnified larger). The spyglass has the converging OBJECTIVE lens, but then a diverging EYEPIECE lens. The light from the distant object on the left side comes into the Objective lens and wants to form a real image {image 1}. But, we intercept that light with the second lens (the diverging eyepiece lens). This make the first real image act as a virtual object for the second lens! This virtual object will create a larger virtual image (as long as the virtual object is essentially at/outside the focal length) 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 spyglass (depending on how far away the initial object is, the first real image will form at slight different places, thus the eyepiece lens has to be adjusted to put the "virtual object" at the focal length of the eyepiece lens). Refresh applet