Optic Instruments

What is optics?

The scientific study of light. Physical optics is concerned with the creation, nature, and properties of light. Psychological optics pertains to the role of light in vision. Geometrical optics deals with the properties of reflection and refraction of light, as part of the study of mirrors, lenses, and optical fibers.

One of the main things we learned in the Junior Cert was that light travelled in straight lines. So to does sound, we are not told this in Junior cert. One of the reasons is because you can hear people around corners, we will talk further about this in the waves topic but for now anything moving will move at a constant speed in a straight line.

Optical effects of nature

optic effects in nature


Greek mathematician Euclid studied mirrors and discovered the laws of reflection. Willebrord Snell discovered the laws of refraction in 1621.

The Arabian physicist, Alhazen (c.965–1038), applied mathematics to his study of plane and curved glasses and mirrors. He showed that spherical mirrors could not bring parallel rays to a sharp focus – spherical aberration – and that light travels more slowly through a more dense medium, causing the bending at interfaces between media of different density.

Solar Ecilipse

Converging lens from Walt

The Microscope

The microscope, which consists of two converging lenses, was invented by Zacharius Janssen about 1590.

In the microscope the first lens is called the objective lens and the object to be viewed is placed just outside its focus, to form a magnified inverted real image. This real image is the object for the second lens, called the eyepiece lens, and is placed just inside the focus of the eyepiece lens. The final image formed is magnified, virtual, still inverted and formed far away from the eyepiece lens so that the it can be viewed with a relaxed eye.


The Telescope


Total internal reflection



lenses overview here


Convex lenses overview here


Rules for Drawing Uniform Lenses ray diagrams

  1. Draw the principal axis
  2. Draw to scale the objecct and image on the principlal axis, or lable the focal point.
  3. Any ray that passes through the centre of the lens continues to travel straight
  4. Any ray that travels parallel to the prinicpal axis come out through the focal point.

The following links provide all the ray diagrams you need

Btw f & 2f


At f


At 2f


Outside 2f


Inside f


Diverging Lens



Some Optics experiments


A site with some experiments to try at home with optic equipment in mind


The very 1st product scanned using the the Universal Product Code was a pack of chewing gum in Ohio in 1974

Use of cameras & focusing