Occular Lens

Occular lens, magnifies the object image into a much larger image.  As seen in Figure 3 the M or the angle of the actual image seen after the occular lens, compare to the O or the angle of the actual object seen without the lens, is much larger.  Therefore to the eye it seems like as if the image is really close to the observer which is the job of a binocular.  So as its transverse from the Objective lens, to the Prism and then to the Occular lens, the image size of the actual object is increased.  To calculate how much angular magnification is coming in the eye is:

Both M and O could be approximated to their Height divided by the distance away from the eye.