How To Increase Magnification On A Microscope?
Magnification: How Large Can You See?
Magnification tells us how much bigger an object appears under a microscope compared to its real size. this is done using two sets of lenses:
- objective lens
- eyepiece (ocular lens)
Most compound light microscopes have two types of lenses–the ocular lens and the objective lens. the ocular lens is the lens on the eyepiece. the objective lens is the lens closest to the object or slide being observed.
Most microscopes have a rotating disc with at least three objective lenses attached, so the observer can choose an appropriate magnification.
Compound simply means the magnification happens in two stages instead of one, which is what lets these microscopes reach much higher powers than a single-lens magnifier ever could.
Objective Lens
This is the main lens close to the specimen. objective lenses come in different powers:
- 4x or 10x (low-power): great for scanning larger areas.
- 40x (high-power): good for seeing more detail in cells.
- 100x (oil immersion): used for the highest magnification and resolution. requires a special oil to reduce light refraction and improve clarity.
Objective lenses (main lenses)
- low-power (4x - 10x): used for scanning large areas of a slide.
- high-power (40x): ideal for detailed study of cells or bacteria.
- oil immersion (100x): used for maximum resolution, with special oil between the lens and slide to reduce light loss.
Objectives typically have magnifying powers that range from 1:1 (1x) to 100:1 (100x), with the most common powers being 4x (or 5x), 10x, 20x, 40x (or 50x), and 100x.
An important feature of microscope objectives is their very short focal lengths that allow increased magnification at a given distance when compared to an ordinary hand lens.
Eyepiece Lens
This is the lens you look through. it usually has a 10x magnification, but some may be different. in digital microscopes, the eyepiece may be replaced by a built-in camera and a screen to view the image.
- usually offers 10x magnification.
- some microscopes offer different magnifications or even built-in digital cameras to capture images or video.
Eyepieces, like objectives, are classified in terms of their ability to magnify the intermediate image. their magnification factors vary between 5x and 30x with the most commonly used eyepieces having a value of 10x-15x.
A standard microscope eyepiece magnifies an object 10x. however, you can find eyepieces that magnify 15x, 20x and even 30x or higher.
Calculating Total Magnification
To find the total magnification, multiply the power of the objective lens by the power of the eyepiece.
Example: a 40x objective lens × 10x eyepiece = 400x total magnification.
In order to measure the total magnification, you must calculate the product of the ocular lens and the objective lens.
- record the magnification of the ocular lens in the eyepiece and record the magnification of the objective lens (these numbers are usually engraved on the sides of both types of lenses).
- next, multiply the ocular lens magnification by the objective lens magnification.
- this will give you the total magnification.
For instance, if you are using an ocular lens with 10x magnification and an objective lens with 50x magnification, your total magnification is 500x.
Total visual magnification of the microscope is derived by multiplying the magnification values of the objective and the eyepiece.
For instance, using a 5x objective with a 10x eyepiece yields a total visual magnification of 50x and likewise, at the top end of the scale, using a 100x objective with a 30x eyepiece gives a visual magnification of 3000x.
Adjusting Magnification
Achieve a wide range of microscope magnification. a standard microscope eyepiece magnifies an object 10x. however, you can find eyepieces that magnify 15x, 20x and even 30x or higher.
This presents a plethora of options in terms of combining the ocular and objective lenses to reach the perfect point of magnification.
To adjust the magnification, simply switch out the ocular and/or the objective lenses until you find the ideal combination for viewing your sample or slide.
Most microscopes have a rotating disc with at least three objective lenses attached, so the observer can choose an appropriate magnification.
If you don’t want to change objectives or get a new eyepiece, the simplest thing is to make the tube longer.
By making the eyepiece sit further back, that increases the primary image distance and decrease the object distance at the same time.
That helps increase the image-object distance ratio and get a higher magnification.
The only draw back is that you have to make sure that the objective can accommodate a smaller working distance; otherwise, the image can’t come into focus if the objective is hitting the glass slide.
Tube Length And Magnification
Total magnification is also dependent upon the tube length of the microscope.
Most standard fixed tube length microscopes have a tube length of 160, 170, 200, or 210 millimeters with 160 millimeters being the most common for transmitted light biomedical microscopes.
Many industrial microscopes, designed for use in the semiconductor industry, have a tube length of 210 millimeters.
The objectives and eyepieces of these microscopes have optical properties designed for a specific tube length, and using an objective or eyepiece in a microscope of different tube length will lead to changes in the magnification factor (and may also lead to an increase in optical aberration lens errors).
Infinity-corrected microscopes also have eyepieces and objectives that are optically-tuned to the design of the microscope, and these should not be interchanged between microscopes with different infinity tube lengths.
These additional lenses will sometimes introduce an additional magnification factor (usually around 1.25-1.5x) that must be taken into account when calculating both the visual and photomicrographic magnification.
This additional magnification factor is referred to as a tube factor in the user manuals provided by most microscope manufacturers.
Thus, if a 5x objective is being used with a 15x set of eyepieces, then the total visual magnification becomes 93.75x (using a 1.25x tube factor) or 112.5x (using a 1.5x tube factor).
Magnification Changers And Empty Magnification
In addition to the parallelizing lenses used in some microscopes, manufacturers may also provide additional lenses (sometimes called magnification changers) that can be rotated into the optical pathway to increase the magnification factor.
This is often done to provide ease in specimen framing for photomicrography.
These lenses usually have very small magnification factors ranging from 1.25x up to 2.5x, but use of these lenses may lead to empty magnification, a situation where the image is enlarged, but no additional detail is resolved.
Remember, the highest magnification is not always the best, as compound light microscopes can really only magnify up to a certain point before the images lose clarity and become unreliable.
However, bigger doesn’t always mean better. high magnification alone doesn’t guarantee a clear image. that’s where resolution matters.
- field of view: higher magnification narrows what you can see.
- depth of field: the range in focus becomes shallower.
- working distance: the space between the lens and specimen gets smaller, which can be tricky for surgical or dental procedures.
Magnifications higher than this value will yield no further useful information or finer resolution of image detail, and will usually lead to image degradation, as discussed above.
Exceeding the limit of useful magnification causes the image to suffer from the phenomenon of empty magnification, where increasing magnification through the eyepiece or intermediate tube lens only causes the image to become more magnified with no corresponding increase in detail resolution.
Resolution: Seeing The Details Clearly
Resolution is the ability of a microscope to show two nearby points as separate. in simpler words, it lets you see sharp, fine details instead of a blurry image.
For optical instruments in general, resolution is the ability to see fine details in an image.
More specifically, resolving power is the ability to distinguish in an image adjacent points or lines of the object which are closely spaced together.
Usually these two terms are used synonymously, however resolution is the more practical one.
Two main factors that affect resolution:
- wavelength of light
- numerical aperture (na)
Shorter wavelengths give better resolution. for example, blue light has a shorter wavelength than red light, which is why fluorescence microscopes use special light sources for high-resolution imaging.
This is a number that tells how well a lens gathers light. a higher na means better resolution. oil immersion lenses often have higher na and are used when the clearest image is needed.
The range of useful total magnification for an objective/eyepiece combination is defined by the numerical aperture of the 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 × na).
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).
Limits Of Optical Enlargement
Viewed through the microscope eyepiece. like all things, even your microscope’s magnification has limits.
Analog microscopes that use light and mirrors to magnify objects usually max out at about 1,500x magnification.
This is because light wavelengths cause the image to appear unclear at that magnitude of magnification.
Electron microscopes, however, can produce images that exhibit impressive clarity all the way up to 200,000x magnification since electrons have much shorter wavelengths.
Most classroom compound light microscopes top out at 1,000x magnification.
That's achieved by pairing a standard 10x eyepiece with a 100x oil-immersion objective lens.
Some entry-level educational microscopes stop at 400x, while some advanced models advertise magnifications up to 2,000x.
However, magnifications beyond about 1,000x often provide little additional detail due to the optical limits of visible light.
It is a common misconception that at 1000x magnification items will be visible under the microscope that are not visible at 400x.
This is not typically true - you can view the same samples at 400x that you will view at 1000x, they will just take up a greater portion of the microscope's field of view at 1000x.
Digital Magnification
Digital magnification is the process of enlarging the image captured by a microscope’s camera using software.
This can be done on a live video feed or a still image, and is similar to zooming in on a photo with your phone or computer.
The system doesn’t change the physical optics—it simply increases the size of the pixels that make up the image.
- optical magnification
- optical magnification is achieved through the physical lenses of the microscope. it increases the level of detail and resolution you can actually see.
- digital magnification
- digital magnificationscales uppixelation—a grainy or blurry image where fine detail is lost.
Digital microscopes use electronic image sensors (camera sensors) to replace eyepieces.
Stereo microscopes have eyepieces and can be equipped with digital cameras.
Digital microscopy allows rapid acquisition of high-quality images.
It is often used for fast and easy documentation, quality control (qc), failure analysis, and research and development (r&d) in a variety of fields.
Field Of View At Higher Magnification
High power compound microscope it can be difficult to determine what you will see through the eyepieces at different magnifications.
The images below were created to help you determine how much of the field of view will be occupied by certain samples at different magnifications.
The following four samples are illustrated to show the microscope field of view at 200x, 400x, 600x and 1000x magnification:
- 200x
- 400x
- 600x
- 1000x
Object field (of) is the part of the object which is reproduced in the final image.
It is also known as the microscope field of view (fov).
Thus, details of an object can only be observed if they are present in the object field.
When looking through the eyepieces, the of is a visible circular image of a portion of the sample.
The object field in digital microscopy is of rectangular shape due to the nature of the image sensor which receives the image and the monitor which displays it.
