Galilean telescope

A Galilean Telescope or a terrestrial telescope is an optical instrument which is used to see the magnified image of distant objects on earth. Galilean telescope consists of a convex lens as objective lens but a concave lens as eye piece. It always forms erect images...

Astronomical telescope

A telescope is an optical instrument which is used to see the distant objects. Telescopes are of two types:     1. Astronomical telescope 2. Galilean telescope or Terrestrial telescope Astronomical Telescope An astronomical telescope is an optical instrument which is...

Compound Microscope

A compound microscope is an optical instrument consisting of two convex lenses of short focal lengths which is used for observing the highly magnified images of tiny objects. The compound microscope can magnify the image of a tiny object up to 1000. Principle of...

Simple microscope

A microscope is an optical instrument which is used to see highly magnified images of tiny objects such as bacteria, cells , viruses and protozoans etc. because these tiny objects cannot be seen by naked eyes. In this chapter we shall study two types of microscopes:...

Cataract, Presbiopia and Astigmatism

Cataract Cataract is usually found in old persons. Cataract causes the loss of eye sight due to the formation of an opaque membrane over the eye lens.               Correction of Cataract This defect cannot be corrected by using any type of spectacles. The only method...

Hyper-metropia or Long-sightedness

Due to Hypermetropia the eyes are able to see the distant objects clearly but cannot see the nearby objects clearly. In this case the image of nearby object is formed beyond the retina. Cause of Hypermetropia An eye suffers from Hypermetropia due to the following two...