Waves and Optics - Geometrical Optics I

5. Geometrical Optics II

Gregory Telescope

The camera lens and impact of focal length
Two lenses used to form a "telephoto lens"
Multiple lens systems - use the image formed by one lens as a "pretend" object for the next one
Additional material here on the use of multiple lenses in an endoscope to see inside the body
The microscope - the (strong) objective lens forms an enlarged real image of a nearby object, and the eyepiece acts as a magnifying glass to view this real image.
The telescope - the first (weak) lens forms a real image of the distant object, and the eyepiece acts as a magnifying glass to view this real image.
Curved mirrors for imaging - mirrors have the advantage of no chromatic aberration (focal length varying with wavelength), and are used widely, particulary so in astronomical telescopes. The focal length of a spherical mirror is half its radius of curvature. To deal with calculations, I recommend considering spherical mirrors as the equivalent lens, plus a plane reflector.
Interactive demo of imaging using a spherical mirror From Lightlink
Eyesight correction - I cannot see clearly more than one metre away. But if I put a 1 m focal length diverging lens in front of my eyes, this creates an image of the outside world all within one metre of me, where I can see it clearly. Long sightedness can be corrected in a similar way, but using converging (positive) lenses.

Similar material to that presented in the lectures is available at:-

Created by, and copyright of, Bruce Sinclair, University of St Andrews; last modified 18/09/01