Appendix - The eye and sight - questions

1 - Draw a picture of the eye and describe the structure.

2 - What is accommodation ?

3 - What is depth of vision ?

4 - What is the near point ?

5 - Explain how the retina works.

6 - Sketch a graph that explains how colour vision works.

7 - What is photopic vision ?

8 - What is scotopic vision ?

9 - What is the visible spectrum ?

10 - What are the primary colours of light ?

11 - What are the secondary colours of light ?

12 - How does filters work ?

13 - What is perception ?

Appendix - The eye and sight

The structure of the eye

1. The cornea is a layer of transparent skin that protects the eye.
2. The lens focus light on to the retina.
3. The retina turns light into nerve signals.
4. The nerve signals are sent to the brain via the optical nerve.

Accommodation

The lens can change shape to focus on things closely or far away. This is done by the ciliary muscles pulling on the lens and it is called accommodation.

Depth of vision

The near point

The retina

1. The retina contains two types of receptor cells called rods and cones.
2. Rods detects motion and peripheral vision (and to see in low light).
3. Cones are needed for colour and a sharp vision (acuity).
4. There is a yellow spot in the retina were most of the cones are located (see figure below).

Colour vision

There are three different types of cones that are sensitive to different wavelengths. They are called blue, green and red and their sensitivity is shown in the figure below.

Photopic vision

Scotopic vision

The visible spectrum

The visible spectrum is the portion of the electromagnetic spectrum that is visible to (can be detected by) the human eye. Electromagnetic radiation in this range of wavelengths is called visible light or simply light. Remember that a photon can only have one specific wavelength but that normally light consists of many different photons with many different wavelength. The exception is laser light where the light only have one wavelength.

The primary colours

The secondary colours

Yellow, Magenta and Cyan are secondary colours.

A mixture of two primary colours will give light that looks yellow, magenta or cyan to the human eye.

Filters

A primary filter stops all photons except those of a particular wavelength.

For example, if white light is shone through a red filter, then all the wavelengths will be absorbed except for red. Only red light will be transmitted through a red filter.

A secondary colour filter will stop all photons except those of two wavelengths.

For example, if white light is shone through a magenta filter, then all the wavelengths will be absorbed except for red and blue. Only red and blue light will be transmitted through a magenta filter.

Perception