How does an optical microscope work

How does a microscope work?

A microscope magnifies very small things and structures. But how exactly does a (light) microscope work? In principle, the way it works is very simple: With the help of lenses, the light rays are refracted so that an optically enlarged intermediate image (so-called "real intermediate image") is created. This "real intermediate image" of the objective is then enlarged to form a "virtual intermediate image" with the aid of the eyepiece, which acts like a magnifying glass. It is also called a "compound microscope" because there are basically two magnification steps. (For a detailed explanation see below)

Unlike the Telescope, where things only appear small because of the great distance, you can use a microscope to enlarge things that are located a short distance in front of the eye.

The following graphic illustrates how a microscope works by following the course of the light. You can see that it penetrates at least two lenses - as a rule there are four, because nowadays both the objective and the eyepiece each consist of two lenses. In addition, you usually have to include the lens of the eye in the process - with the digital microscope, however, a camera is used instead of the eye.

The light is emitted from the light source. It penetrates the object that is on the slide that is clamped on the stage. The light rays are enlarged through the lens. An enlarged "real intermediate image" is created in the tube. This is clearly enlarged again by the eyepiece.

Understanding exactly how a microscope works requires some basic knowledge of optical phenomena. The following is a step-by-step derivation.

Transparent bodies refract light

Light moves through the vacuum at the speed of light. However, it is slowed down by solid substances (e.g. water or glass). In the figure below, the light is shown by dotted lines. It moves faster in the air than in glass.

When light hits an inclined transparent surface, it does not go straight through, but is deflected. This phenomenon is known as "light refraction", so the path of the light rays is deflected.

Principle of lenses (converging lenses, diverging lenses)

With the help of lenses, the refraction of light can be used in a targeted manner. There are basically two types of lenses: converging lenses (convex) and diverging lenses (concave).

First of all for Converging lens: their surfaces are convex. Rays of light. which fall parallel on the converging lens are refracted by the glass in such a way that they meet behind the lens at a common point. This point will too Focus called, the distance between the lens and the focal point is called Focal length.

Exactly the other way around is the case with one Diffusing lens. Your surface is concave arched. The light rays falling parallel on the lens are deflected apart. It is called "scattered". With the light microscope, however, only the functionality of a converging lens is relevant.

For the sake of completeness, here is how a diffusing lens works:

More about the difference between concave and convex (including motto).

How a magnifying glass works

To understand how a microscope works, one must first think about magnifying glasses. A magnifying glass is a collecting lens, usually on a handle. But why does a magnifying glass enlarge? The solution to the riddle is a "virtual image", which is generated by the lens. This enlarged virtual image is then displayed correspondingly larger on the retina in the eye - you see the object or the object larger. In the following graphic you can see the normal view of an object above, which is shown relatively small on the retina. Below, the magnifying glass creates a virtual image that is shown much larger on the retina.

The compound microscope

A microscope now consists of two parts: the objective creates a "real image" in the microscope, which is then further enlarged with the help of the eyepiece, which acts like a magnifying glass. This creates a typical beam path that is often used for the functionality of the microscope. The following figure illustrates the beam path in the microscope:

The following video illustrates the process:

The following stamp from 1968 illustrates the principle once again:

Books on microscopes / microscopy

The following list contains some products that can be ordered directly from Amazon. A click on the price opens the Amazon page (* partner link). Please note that the prices are without guarantee, as they can change at short notice.

product description Price on Amazon *


  • Hardcover: 48 pages
  • Franckh Kosmos Verlag (June 2014)
  • Language: German
  • Recommended age: from 8 years
  • How does a microscope work? What can you discover with it? How are protozoa, minerals, plant and animal cells structured? This book helps you choose the right microscope and describes how to use it from the ground up. It is explained step by step which magnification is the right one, how to make your own preparations and how to make permanent preparations.

€ 9.99 (Amazon)

What's what? Microscope (volume 8)

  • Hardcover: 48 pages
  • Tessloff Verlag (November 2016)
  • Language: German
  • Recommended age: from 8 years
  • In science and research - for example in medicine and forensics - the microscope is indispensable. WHAT IS WHAT goes on an excursion: Who invented the microscope? How does it work? Where exactly is it used? Great photos, infographics and tips for your own experiments included.

€ 9.95 (Amazon)

The great cosmos book of microscopy

  • Hardcover: 320 pages
  • Publisher: Franckh Kosmos Verlag; Edition: 3 (June 11, 2015)
  • Language: German
  • This book is the recipe, instruction and work book for microscopists, which conveys extensive knowledge and describes it in a very understandable way. From viruses in house plants to the bizarre protozoa from the garden pond to the examination of blood cells, this book encourages you to carry out your own analyzes. It introduces all the important techniques for processing simple and demanding objects.

€ 39.99 (Amazon)

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* Note on the Amazon partner links

The prices link to the respective Amazon product page (so-called partner link). A reference to this page as the source is transmitted via the URL ("light microscope-21"). If you buy the product now, the operator of this site will receive a so-called. Advertising expense reimbursement from Amazon. The product costs just as much as usual.

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