What is Magnification in Microscope?
Magnification in microscopes refers to the amount or degree of visual enlargement of an observed object. Magnification is measured by multiples, such as 2X, 4X, and 10X, indicating that the object is enlarged to twice as big, four times as big, or 10 times as big, respectively.
Magnification in microscopes results from a complex interaction between visible light waves and the curvature of the lens.
When a beam or ray of light is transmitted through airstrikes and passes through the convex surface of the glass, it experiences some degree of refraction, defined as the bending or change in the angle of the light ray as it passes through a medium such as a lens.
The greater the difference in the composition of the two substances the light passes between, the more pronounced the refraction. When an object is placed a certain distance from the spherical lens and illuminated with light, an optical replica, or image, of it is formed by the refracted light.
Depending upon the size and curvature of the lens, the image appears enlarged to a particular degree, which is called its power of magnification and is usually identified with a number combined with × (read “times”).
This behavior of light is evident if one looks through an everyday object such as a glass ball or a magnifying glass. It is basic to the function of all-optical, or light microscopes, though many of them have additional features that define, refine, and increase the size of the image.
How Magnification Works in Microscopes?
When you look through a simple light microscope or a magnifying glass, you are looking through a biconvex lens (one that’s bent like the back of a spoon on both sides) made of glass.
Magnifying lenses make objects appear larger because their convex lenses (convex means curved outward) refract or bend light rays so that they converge or come together. In essence, magnifying glasses trick your eyes into seeing something different than it really is.
When light bounces off an object and travels to your eyes, those light rays travel parallel to each other. When they pass through a magnifying lens, the convex lens bends the parallel rays so that they converge and create a virtual image on your eyes’ retinas.
That virtual image on your retinas appears larger than the real object due to principles of geometry. Despite the magnifying lens, your eyes trace the light rays back in parallel lines to the virtual image. Since the virtual image is farther from your eyes than the object is, the object appears bigger!
So really what this means is that when you are looking through your microscope you are not seeing the “real” specimen you are seeing a reproduced and enlarged image of the specimen.
Modern compound microscopes contain an eyepiece, an objective lens, and a condenser lens and together these lenses work to refract the light that enters our eye and serve to enlarge the specimen under inspection.
In fact, the objective lens has within it, several compounding lenses that contribute to higher and higher the power of magnification in microscopes.
What is a Useful Magnification Range?
The “useful” magnification in microscopes is between 500 × NA (numerical aperture) and 1,000 × NA. Some light microscopes boast enormous magnification, but practically speaking, the limit is just under 1,400X. Specialists call everything beyond that “empty magnification.” Though structures appear larger, no additional details are resolved.
The range of useful magnification in microscopes for an objective lens/eyepiece combination is defined by the numerical aperture of the microscope optical system.
There is a minimum magnification necessary for the detail present in an image to be resolved, and this value is usually rather arbitrarily set as 500 times the numerical aperture (500 x NA) and defined by the equation:
Useful Magnification (total) = 500 to 1000 × NA (Objective).
At the other end of the spectrum, the maximum useful magnification of an image is usually set at 1000 times the numerical aperture (1000 × NA) as given by the equation above.
Magnifications higher than this value will yield no further useful information or the finer resolution of image detail, and will usually lead to image degradation.
What are Magnification Limits in Microscope?
For a standard light-based microscope, the maximum magnification in microscopes extends up to 1,500X; beyond this, objects under view become excessively fuzzy because the wavelengths of light limit the clarity of images.
Electrons, on the other hand, have much shorter wavelengths. According to Auburn University, electron microscopes produce useful images with magnifications up to about 200,000X.
What Are The Magnifying Parts of Microscope?
Modern microscopes contain a series of lenses rather than just one. They have an objective lens (which sits close to the object) and an eyepiece lens (which sits closer to your eye). Both of these contribute to the magnification of the object in the microscope.
The eyepiece lens usually magnifies 10X, and a typical objective lens magnifies 40X. (Microscopes usually come with a set of objective lenses that can be interchanged to vary the magnification.).
There are three types of objective lenses: 4X (scanning objective)
- 10X (Low power objective lens).
- 40X (High power objective lens).
- 100X (Oil immersion objective lens).
Including more lenses doesn’t change the basic principle of how a microscope magnifies but it does enable higher magnifications and gives a better-quality image.
How Is Total Magnification Calculated in Microscope?
The total magnification in microscopes is understood as the magnification of the objective lens multiplied by that of the optical lens.
However, before calculating total magnification first you have to determine the magnification strength of the optical lens. This should be written on the outside of the eyepiece, but if it is not look in the manual. Generally speaking, the ocular lens magnifies 10X.
Determine the magnification capacity of the objective lens. The magnification is written on the side of the lens. Traditionally, the value could be 4X, 10X, 40X, or 100X. If you are not sure of the magnification power, check the manual.
The objective lens is located on the rotating wheel just above the stage or platform where you place the microscope slide. In some instances, the microscope may have only one lens, but generally, it has three to four.
To calculate the total magnification of the compound light microscope multiplies the magnification power of the ocular lens by the power of the objective lens. For instance, a 10X ocular and a 40X objective would have a 400X total magnification. The highest total magnification for a compound light microscope is 1000X.
Factors Affecting Magnification Change
Changing from low power to high power increases the magnification of a specimen. As we discussed the amount an image is magnified is equal to the magnification of the ocular lens, or eyepiece, multiplied by the magnification of the objective lens.
Light Intensity Decreases
The light intensity decreases as magnification increases. There is a fixed amount of light per area, and when you increase the magnification of an area, you look at a smaller area. So you see less light, and the image appears dimmer.
Image brightness is inversely proportional to the magnification squared. Given a fourfold increase in magnification, the image will be 16 times dimmer.
Field of View
Going to high power on a microscope decreases the area of the field of view. The field of view is inversely proportional to the magnification of the objective lens.
For example, if the diameter of your field of view is 1.78 millimeters under 10X magnification, a 40X objective will be one-fourth as wide, or about 0.45 millimeters.
The specimen appears larger with a higher magnification because a smaller area of the object is spread out to cover the field of view of your eye.
Depth of Field
The depth of field is a measure of the thickness of a plane of focus. As the magnification increases, the depth of field decreases.
At low magnification, you might be able to see the entire volume of a paramecium, for example, but when you increase the magnification you may only be able to see one surface of the protozoan.
Working Distance
The working distance is the distance between the specimen and the objective lens. The working distance decreases as you increase magnification.
The high power objective lens has to be much closer to the specimen than the low-power objective lens in order to focus. Working distance is inversely proportional to magnification.
Oil Immersion
Microscopes magnify an object’s appearance by bending light. Higher magnification means the light is bent more. At a certain point, the light is bent so much that it can’t make it through the objective lens.
At that point, usually around 100X for standard lab microscopes, you’ll need to put a drop of oil between your specimen and the objective lens. The oil “unbends” the light to stretch out the working distance and make it possible to image at high magnifications.
