positive lenses are thicker in the middle and therefore capable of converging light to a focus. These are termed biconvex, plano-convex, and convex (converging) meniscus.

Function ofstage inmicroscope

Magnification in the compound microscope is achieved by the use of simple lenses. There are two broad categories of simple lenses: positive lenses, which are thicker in the middle (convex), cause light to converge. Negative lenses are thinner in the middle (concave) and cause light to diverge.

The most common shape for experimental prisms is triangular with flat sides, but prisms can be rectangular, hexagonal, trapezoidal or multifaceted. Raindrops, without any facets, can even have prismlike properties. Optical prisms are usually made of glass, plastics or fluorite; they can be divided into three basic categories. Dispersive prisms spread light into separate wavelengths; reflective prisms reverse or flip images through internal reflection; and polarizing prisms separate light by polarization. Polarizing prisms use the same principles as dispersive prisms but are made of a specialized substance that can separate light by the orientation of the light waves.

The most important part of the microscope are the objective lenses. These different lenses allow the viewer to see the specimen at different magnifications and easily switch between the lenses with the revolving nosepiece. The objective lenses in modern compound microscopes are also parfocal, which means that switching from a lower to a higher magnification lens keeps the image roughly in focus. While the fine focus knob may be needed for adjustment, the image stays in view when switching lenses.

What is eyepieceinmicroscope

The effect that the simple lenses has on the light is fundamental to the production of a useful image. Without a condenser, the microscope would be a magnifying glass with no resolving power of its own. The student microscopes are fitted with Abbe (chromatic) condensers. They are simply constructed and transmit a large amount of light.

Newton's triangular prism and the sun catcher in your window both project a rainbow of colors onto the wall. This effect is called dispersion, and it is a byproduct of refraction. The light of the sun is made up of a spectrum of different wavelengths. As different wavelengths hit the prism's surface, they bend at slightly different angles. The shortest wavelengths, which appear violet to the human eye, are bent the most, and the longest wavelengths, which appear red, are bent the least. The result is a fan showing the entire spectrum of visible light.

Internal reflection is used to flip, skew or rotate an image. For example, two prisms are used to flip images upright in binoculars. Although it is called reflection, internal reflection is caused by the refractive angles of the prisms. If the angle of refraction for the prism is larger than the critical angle for that prism, the beam of light will reflect back into the prism until it hits a surface at less than the critical angle and leaves the prism. Internal reflection is also how signals travel through fiber optic cable.

The eyepiece actually has two functions: to magnify and correct. The need for correction comes from the different colours of light that are refracted. If the eyepiece is over-corrected or under-corrected, the different colours of light will not be balanced and the resulting image will show up as coloured.

Function ofbody tube inmicroscope

Earlier on, we said that the microscope is able to magnify and resolve an image, to allow the viewer to see tiny details in the sample. The lenses accomplish the magnification of the image, but the resolution is more complex. Many factors influence the highest resolution a microscope can achieve, such as:

We have discussed the objective and eyepiece lenses, but another part of the microscope has lenses also: the condenser. Unlike the objective and eyepiece lenses, which serve to magnify the image to the viewer, the lenses in the condenser are there to focus the light on the sample. This is accomplished by combining several simple lenses together. The combinations of lenses used in the condenser can vary, from something like this:

What is the function ofarm inmicroscope

Based in Wenatchee, Wash., Andrea Becker specializes in biology, ecology and environmental sciences. She has written peer-reviewed articles in the "Journal of Wildlife Management," policy documents,and educational materials. She holds a Master of Science in wildlife management from Iowa State University. She was once charged by a grizzly bear while on the job.

Basemicroscope function

Refraction describes how light bends as it moves from air to another clear medium. Refraction is the reason that a straight rod appears to have a kink when you put it in a glass of water. As a beam of light encounters the surface of a prism, it slows a bit. The slowing changes the angle at which the light moves. The light bends again as it exits the prism. The angle between the two surfaces is called the refracting angle and how much the medium bends the light is its refractive index .

The microscope is the fundamental tool of the cytologist. In order to use it effectively, you need to understand key concepts, like:

Function of microscope

Microscopeparts and functions

negative lenses are thinner in the middle so that rays of light passing through them are made divergent termed biconcave, plano-concave, concave (diverging) meniscus

As an additional note: Lens magnification is based on standard microscope sizes, including the size of the tube the lenses are installed in. If this standard size is changed, so will the magnification.

The image we see through the eyepiece is the aerial image formed by the microscope objective in the tube. This image has a limit, where useful magnification ends and the empty magnification begins. There is a good parallel with the grain of a photographic film. As soon as the image details reach the same size as the image grain, no further detail can be gained by magnifying the image. In the same way, as you move closer and closer to the photographic image on a projector screen, you reach the point where you can no longer see the actual details on the photograph. The performance limit of the microscope is determined by the NA, so that the total magnification of the microscope is the objective magnification multiplied by the eyepiece magnification  times NA.

Comparison of dry and oil immersion objectives. The values for NA range from 0.1 to 0.95 for dry objectives and up to 1.5 for oil immersion lenses. Air has a refractive index of 1. So for air, the image scatters beyond the aperture angle.  Immersion oil fills the space between the cover glass and the front lens of the microscope has a refractive index of 1.5. Oil keeps the image within the aperture angle of the objective lens.

Function ofnosepiece inmicroscope

All these factors determine the resolving power, or the minimum separation of two objects such that they appear distinct and separate when viewed through a microscope or telescope. The numerical aperture (NA) is a measure of the resolving power of the objective lens only. The upper limit of resolving power, of an objective lens or the whole microscope, ultimately depends on the wavelength of light used. Why can't we just magnify the image?

Isaac Newton used a prism to discover how light can be broken into its component wavelengths, or colors. Prisms can be made from any clear compound and are generally cut with specially angled facets. The defining optical property of prisms is that they bend light. The material that the prism is made from and the number and angle of the facets affect how light coming through the prism is reflected, refracted and dispersed.

NA is calculated using a mathematical formula devised by Ernst Abbe for the direct comparison of the resolving power of dry and all types of immersion objectives.

Angular Apertures of Objectives Compared. The 3x objective is at a longer focal length, taking in a larger area at a smaller angle. The 95x objective is at a shorter focal length, taking in a smaller area in a larger angle.

These broad categories contain three lenses each, to make the six simple lenses. Positive lenses are biconvex, planoconvex, and convex (converging) meniscus, while negative lenses are biconcave, planoconcave, and concave (diverging) meniscus.

The compound microscope allows the observer to see greater detail in small objects by magnifying and resolving the image. Although chromosomes cannot be seen by the naked eye, even a relatively low-power compound microscope will allow a scientist to resolve individual chromosomes in the eukaryotic cell.