how does the lens of a light microscope work?

A light microscope works very much like a refracting telescope, but with some minor differences.
A telescope must gather large amounts of light from a dim, distant object; therefore, it needs a large objective lens to gather as much light as possible and bring it to a bright focus. Because the objective lens is large, it brings the image of the object to a focus at some distance away, which is why telescopes are much longer than microscopes. The eyepiece of the telescope then magnifies that image as it brings it to your eye.
A light microscope must gather light from a tiny area of a thin, well-illuminated specimen that is close-by. So the microscope does not need a large objective lens. Instead, the objective lens of the microscope is small and spherical, which means that it has a much shorter focal length on either side. It brings the image of the object into focus at a short distance within the microscope’s tube. The image is then magnified by a second lens, called an ocular lens or eyepiece, as it is brought to your eye.

How microscopes work

Microscopes are effectively just tubes packed with lenses, curved pieces of glass that bend light rays passing through them. The simplest microscope of all is a magnifying glass made from a single convex lens, which typically magnifies by about 5–10 times. Microscopes used in homes, schools, and professional laboratories are actually compound microscopes and use at least two lenses to produce a magnified image. There’s a lens above the object (called the objective lens) and another lens near your eye (called the eyepiece or ocular lens). Each of these may, in fact, be made up of a series of different lenses. Most compound microscopes can magnify by 10, 20, 40, or 100 times, though professional ones can magnify by 1000 times or more. For greater magnification than this, scientists generally use electron microscopes.

So what does a microscope actually do? Imagine a fly sitting on the table in front of you. The big, fat, compound eye on the front of its head is just a few millimeters across, but it’s made up of around 6000 tiny segments, each one a tiny, functioning eye in miniature. To see a fly’s eye in detail, our own eyes would need to be able to process details that are millimeters divided into thousands—millionths of a meter (or microns, as they’re usually called). Your eyes may be good, but they’re not that good. To study a fly’s eye really well, you’d need it to be maybe 10–100 cm (4–40 in) across: the sort of size it would be in a nice big photo. That’s the job a microscope does. Using very precisely made glass lenses, it takes the minutely separated light rays coming from something tiny (like a fly’s eye) and spreads them apart so they appear to be coming from a much bigger object.

How does a microscope work?

Microscopes can largely be separated into two classes, optical theory microscopes and scanning probe microscopes.

Optical theory microscopes are microscopes which function through the optical theory of lenses in order to magnify the image generated by the passage of a wave through the sample. The waves used are either electromagnetic in optical microscopes or electron beams in electron microscopes.

Optical microscopes

Main article: Optical microscope

Optical microscopes, through their use of visible wavelengths of light, are the simplest and hence most widely used type of microscope. They serve uses in many fields of science, particularly biology and geology.

Optical microscopes use refractive lenses, typically of glass and occasionally of plastic, to focus light into the eye or another light detector. Typical magnification of a light microscope is up to 1500x with a resolution of around 2 micrometres. Specialised techniques (e.g., scanning confocal microscopy) may exceed this magnification but the resolution is an insurmountable diffraction limit.

Other microscopes which use electromagnetic wavelengths not visible to the human eye are often called optical microscopes. The most common of these, due to its high resolution yet no requirement for a vacuum like electron microscopes, is the x-ray microscope.

Because of their popular use, optical microscopes have many adaptions to facilitate usage and improve image quality.

Main articles: Optical microscope and microscopy

Electron microscopes

Main article: Electron Microscope
Electron microscope
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Electron microscope

Electron microscopes, which use beams of electrons instead of light, are designed for very high magnification usage. Electrons, which have a much smaller wavelength than visible light, allow a much higher resolution. The main limitation of the electron beam is that it must pass through a vacuum as air molecules would otherwise scatter the beam.

Instead of relying on refraction, lenses for electron microscopes are specially designed electromagnets which generates magnetic fields that are approximately parallel to the direction that electrons travel. The electrons are typically detected by a phosphor screen, photographic film or a CCD.

Two major variants of electron microscopes exist:

* Scanning electron microscope: looks at the surface of bulk objects by scanning the surface with a fine electron beam and measuring reflection. May also be used for spectroscopy.
* Transmission electron microscope: passes electrons completely through the sample, analogous to basic optical microscopy. This requires careful sample preparation, since electrons are scattered so strongly by most materials. It can also obtain detailed information on the sample’s crystallography through selected area diffraction.

Scanning probe microscope

In scanning probe microscopy (SPM), a physical probe is used either in close contact to the sample or nearly touching it. By rastering the probe across the sample, and by measuring the interactions between the sharp tip of the probe and the sample, a micrograph is generated. The exact nature of the interactions between the probe and the determines exactly what kind of SPM is being used. Because this kind of microscopy relies on the interactions between the tip and the sample, it generally only measures information about the surface of the sample.

Some kinds of SPMs are:

* Atomic force microscope
* Scanning tunneling microscope
* Electric force microscope
* Magnetic force microscope

How does a compound light microscope work?

To comprehend how the compound light microscope (also called a “bright field” microscope) works we must first understand that convex lenses bend light rays in a peculiar manner so that light hitting the center of the lens goes straight through. But light hitting other areas is bent toward a focal point. This bending allows the view at a specific distance from an object to see the image as larger than it would appear to the naked eye.