Main Difference – Telescope vs. Microscope
Telescopes and microscopes are two instruments used to look at magnified images of objects. Both types of instruments could use an objective lens, which produces an image of the object. An eyepiece is then used to look at a magnified version of the image. The main difference between telescope and microscope is that microscopes are used to magnify small objects that are at a short distance from the viewer whereas telescopes are used to magnify large objects that are at a large distance from the viewer.
What are Telescopes
In refracting telescopes, there are typically two convex lenses. One lens acts as the objective lens: this lens gathers light from faraway objects and forms a real, inverted image of the object at its focal point. A second lens, called the eyepiece, is positioned such that the image formed by the objective lens is at its focal point. When an observer looks through the eyepiece with a relaxed eye, they are able to see an object of the image, formed at infinity. The ray diagram for a refracting telescope is shown below:
Reflecting telescopes, on the other hand, use a concave mirror as an objective. There are several designs for reflecting telescopes. The ray diagram for a common type of reflecting telescope with an eyepiece on the side is shown below:
The above two types of telescopes are optical telescopes (they use lenses to refract visible light). However, nowadays there are many other types of telescopes in use. For instance, there are radio telescopes, composed of arrays of radio antennas:
What are Microscopes
Microscopes are used to look at magnified images of small objects. A simple microscope (a “magnifying glass”) consists of a single convex lens. The lens is held close to the object so that the object is between the lens and its focal point. When viewed from the other side of the lens, a magnified, virtual, upright image is seen. The compound microscope is the most common type of microscope used in laboratories. With these microscopes, an objective lens is used to create an inverted, real image of the object. Using the eyepiece, the image is magnified. In this sense, its operating principles are similar to that of a refracting telescope:
The ray diagram for a compound microscope is:
Just as it was with telescopes, microscopes are not limited to optical ones either. Electron microscopes use a beam of electrons to look at things at the cellular scale. Scanning tunneling microscopes (STM) can be used to observe objects at the atomic scale.
Difference Between Telescope and Microscope
Size of Objects
Telescopes are used to look at objects that are large (planets, stars, galaxies)
Microscopes are used to look at objects that are small (microorganisms, cells, organelles)
Distance to the Object
Telescopes are situated far away from the object.
Microscopes are placed close to the object.
“Telescope ray diagram for an image at infinity.” by The Open Door Web Site (http://www.saburchill.com/physics/chapters3/0018.html) [CC0 1.0], via Wikimedia Commons
“Diagram of the lightpath through a Newtonian telescope.” by Krishnavedala (Own work) [CC BY-SA 4.0], via Wikimedia Commons
“Atacama Compact Array (ACA) on the ALMA high site at an altitude of 5000 metres in northern Chile…” by ESO (http://www.eso.org/public/images/ann13040a/) [CC BY 4.0], via Wikimedia Commons
“Self-Portrait with Magnifying Glass” by Steven Pisano (Own work) [CC BY 2.0], via flickr
“Diagram of a compound optical microscope with a lens close to the object…” by Fountains of Bryn Mawr (Own work Based on this and this work and distributed under the same license) [CC BY-SA 3.0], via Wikimedia Commons