Science 8 – Unit C: Light and Optical Systems

Topic 5: Extending Human Vision

Telescopes

• Telescopes exist to do two things: magnify distant objects, and collect as much light as possible from very dim sources of light. The bigger the telescope, the more light it collects.

Telescopes Cont’d• The size of the telescope’s objective

lens/mirror helps determine its resolving power. The larger the objective, the more detail you can see. To see any detail in Mars, for example, a 6” objective is minimum.

• A telescope collects light with its objective lens or mirror. This is the larger lens that light must refract through or reflect off of. The telescope we use has a 6” objective mirror.

Telescopes Cont’d

• A telescope focuses its light onto the eye of an observer through the eyepiece lens. The larger the eyepiece the better the image quality. Eyepiece lenses are usually convex.

• The larger the distance between the image and the eyepiece lens, the larger the magnification. This distance is called the focal length of the telescope.

Types of Telescopes

• There are three main types of telescopes, each with their own advantages and disadvantages.

• I. Refractor Telescope -

1. Refractor Telescope• Objective: Convex Lens• Features: Collects light

through a lens which is then focused onto the eyepiece.

• - Used by Galileo to support Heliocentric Model.

• Advantages: Can produce the best quality images.

• Disadvantages: Very expensive to make larger objective lenses.

• Color of objects is often distorted (Halo Effect).

2. Reflector Telescope• Objective: Concave Mirror• Features: - Collects light

through a concave mirror which is then focused onto a secondary mirror and finally passed to the eyepiece lens.

• - Invented by Newton Advantages: Much cheaper than refractors.

• - Can be made much larger, and therefore can see deeper into space.

• Disadvantages: - Images not as sharp as with refractors.

3. Combination Telescope

• Objective: Concave Mirror• Features: Light first focused by

lens onto concave objective mirror which is then reflected onto secondary mirror and finally focused through opening in objective mirror to eyepiece.

• Advantages: - Produces good quality images.

• - Very powerful for its size • - Very Portable Disadvantages:

- Expensive.

Binoculars

• Binoculars are two reflecting telescopes attached side by side.

• The light is reflected by two prisms (see fig. 3.42 on p. 223). This folds the light path and allows the binoculars to have a longer focal length than the actual tube length making them more convenient to use.

Magnifying Lenses and Microscopes

• Magnifying glasses are a simple convex lens used for magnifications of up to 10X the object size.

• Compound light microscopes use two lenses to magnify objects up to 2000X. Both lenses used: objective and eyepiece, are convex to focus the image. Modern day microscopes use multiple lenses instead of just one objective lens and one eyepiece to improve the sharpness of the image.

Importance of Microscopes and Telescopes to Science

• Because of microscopes Robert Hooke discovered that all living things are made of cells. We now know how to cure diseases and study the human organism with microscopes.

• Before the telescope was invented people relied on religion and superstition to explain things. Thanks to the telescope, we now more about our place in the universe.