Microscopy Scales: measurement in themicro-small world.
Text by Alan Maude, Images by Maurice Smith1996
The Universe is so big that it appears infinite in size. Ourearthly measurements dwindle into insignificance when applied toit. Miles or kilometres just run into too many zeros whenrecording distances between galaxies. To make things easier, newmeasures on a scale equal to these vast distances are required:light-years and parsecs! A light year is the distance that lightwould travel in the time it takes the earth to orbit the sun forone complete revolution: the distance light travels in space inone earth year.
At the microscopic level, a similar problem exists. Creatures,invisible to the eye, are often less than a single millimetre inlength. Take a look at a ruler to see just how small this is!
Measurement: a scientific tool.
Measuring things is an important aspect in all scientificdisciplines. It gives us the capacity to relate and model thethings we observe. For example, how would you like a five minutewrestling bout with another person who was 3 metres tall and 1metre across? Probably, you wouldn't! Knowing the size ofsomething helps us to assess cause and effect.
Many people may scoff at such a simple device as a ruler. Yetit is probably the first thing we will use in our formaleducation as a way to understand and help us record details aboutthe things we observe. At Micscape, we are mainly involved withobserving and discussing things which are not easily seen withthe naked eye. We need a way to measure very small things and weneed to understand the scale of the things we observe to considerpart of their relationship with other things in a similarenvironment.
Our measurement of distance at the human scale of existencerevolves around the root distance called the metre. This is theInternationally accepted unit of length and is one of the sevenagreed International System of Units (SI).
Most people can retain a mental model of what a metre is (along stride by an adult), and can judge distances based on itsroot. A 'mental-model' is important. It gives us a 'feel' forsize which enables rapid judgements to be made in the absence ofaccurate data. How high can you jump: 1 metre, 3 metres or 9metres? As soon as the question is asked, you start imagining a'height' and your capacity to leap it.
Distances on our planet can normally be described in 1000metre sections: the kilometre. If you had a journey to make, youwould probably wish to know how far you were going (inkilometres) because it would help you to assess the time it wouldtake to get to where you were going to, the cost in transportterms, and if far enough - climatic changes you can expect.
The scientific world needs to be certain of the size of thingsand this requirement is equally important to the microscopist.Measurements taken of subjects smaller than our ability to seewith the unaided eye still need to be relative to our standardroot measure of 1 metre.
A microscopist's units are as follow:-
1 centimetre (cm) = 0.01 metres (m) or 1 x (10to the power of -2) metres.
The single unit of 1 centimetre is visible.Take a look at a ruler to see how easy this length is to see. Youwill notice a centimetre has tiny divisions, in fact - 10 to eachcentimetre. Each division represents 1 tenth of a centimetre andis called a millimetre.
1 millimetre (mm) = 0.001 metres (m) or 1 x(10 to the power of -3) metres.
Notice just how small but still visible a millimetre ison a ruler. A millimetre is about the size of objects that wehumans can still manage to manipulate with our hands withoutusing devices and tools to help us.
It is the sub-division of this tiny unit which is used tobegin measuring forms normally invisible, or nearly invisible, tothe naked eye: a micron
The micron (um)
Note: The 'u' would normally have a longtail in the left vertical bar, but for the sake of showing thischaracter on all web browsers, we have used the character 'u'instead! The picture below shows the correct shorthand for themicron.
1 micron = 0.000001 metres (m) or 1 x (10 tothe power of -6) metres.
The name 'micron' is actually derived from micrometre.It is very important to remember that there are 1000microns to a millimetre! When you see the size ofa microscopic subject quoted as, say - 800 microns in length and500 microns in width, you can mentally realize this is nearly amillimetre long and half a millimetre across; if you look againat what a millimetre looks like on your ruler, you will see thata subject (or object) is still visible to the naked eye. However,something which is 10 microns x 10 microns could not be seenwithout a microscope!
Scale at the microscopic level
To put things in perspective, we need to consider somemicroscopic subjects and their size. Most people will have heardof an Amoeba. The typical size of this microscopic animal is 0.8mm ( 8/10 of a millimetre) long by 0.4mm (4/10 of a millimetre)wide: just about visible to the naked eye! Measured in microns,the creature is quite large - 800 microns by 400 microns. It is agood reference size to consider smaller life-forms and objectsagainst.
Euglena, a protozoan, is typically 130 x 50 microns - muchsmaller than our large amoeba. It uses a whip like tail called aflagellum to propel itself through water at the rate of 20 to 200microns per second. Compare this speed to its own body-length andthan consider this to the speed of a Paramecium, anotherprotozoan "weighing-in" at 240 x 80 microns; the latteruses cilia (tiny hairs) to move through the water at 400 to 2000microns per second.
The Paramecium moves 10 times faster than the Euglena in realterms! Is it still faster in relative terms, e.g.. speed relativeto the length of each creature's body?
As a rough guide, cells typical to plants and animals arecalled eukaryotic cells and range in size from 10 to 150 microns.
Smaller and smaller
Bacteria, which are much smaller than any of the other formsand cells discussed so far, are typically between 1 micron to 10microns in length; the latter being the length of the rod-shapedbacteria. If you look at the millimetre scale on your ruler, youcan try and visualize 1000 bacteria lined up in a chain betweenthe two marks indicating a millimetre width... or maybe just 8Euglena "nose-to-tail".
An interesting point to note isthat a single human sperm is only 2.5 microns across its widestpart! Around 400 of them could line up across the 1 mm notch of aruler.
The optical microscope can resolve images of microscopic formsup to around 1600x magnification. Some subjects (object?) arejust too small to be made visible using this type of instrument.A top quality optical light microscope can resolve two pointsthat are ca. 0.25 microns apart.
A lower level of the microscopical world existswhich is still populated with living forms called viruses.These are so tiny - typically around 0.1 microns - that they defymeasurement when using the micron as a standard. Instead of themicron, we need to switch to using another unit called the nanometre(nm).
1 nanometre (nm) = 0.000000001 metres (m) or 1x (10 to the power of -9) metres.
There are 1000 nanometres to a micron!Therefore, our virus of 0.1 microns is actually 100 nanometres(nm) long. To see a virus, you would need to use an electronmicroscope, which utilizes a fine beam of electrons to probethe subject and resolve an image up to 50,000x that of an opticallight microscope.
by Alan Maude
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Measuring with a microscope - YouTube
Microscopy is the technical field of using microscopes to view samples & objects that cannot be seen with the unaided eye (objects that are not within the resolution range of the normal eye).
Your microscope may be equipped with a scale (called a reticule) that is built into one eyepiece. The reticule can be used to measure any planar dimension in a microscope field since the ocular can be turned in any direction and the object of interest can be repositioned with the stage manipulators.
In order to know how many microns each scale division represents with each objective turns out to be simplicity itself. Divide the 100 microns by the objective power. A 4X objective = 100/4 = 25 microns per division. A 10X objective = 100/10 = 10 microns per division.
micrometre, also called micron, metric unit of measure for length equal to 0.001 mm, or about 0.000039 inch. Its symbol is μm. The micrometre is commonly employed to measure the thickness or diameter of microscopic objects, such as microorganisms and colloidal particles.
- Stage Micrometer -a microscope slide (generally 1" x 3") that has a ruler etched on it. ...
- Eyepiece Reticle (or reticule) -a small piece of glass with a ruler etched into it that fits into a microscope eyepiece.
There are three basic types of microscopes: optical, charged particle (electron and ion), and scanning probe. Optical microscopes are the ones most familiar to everyone from the high school science lab or the doctor's office.
The chief differences between the two microscopes are that the TEM gives a two-dimensional picture of the interior of the sample while the SEM gives a three-dimensional picture of the surface of the sample.
Scale bar 100 µm (40x magnification).
The basic formula that is used for calculating the scale factor is, Scale factor = Dimension of the new shape ÷ Dimension of the original shape. In case, if the original figure is scaled up, the formula is written as, Scale factor = Larger figure dimensions ÷ Smaller figure dimensions.
Reading a Map - Understanding and Using a Scale - YouTube
Generally speaking, the human eye can see debris and dust that are approximately 25 microns in size. To understand just how small this is, consider that a single hair from your head averages about 70 microns in diameter or 30 times larger than the largest fine particle.
bags how to measure - YouTube
|Objective||Diameter Of Field Of View||Magnification (10x Ocular)|
|40x||0.4 mm (0.45)||400x|
|100x||0.2 mm (0.178)||1000x|
*To figure the length of one cell, divide the number of cells that cross the diameter of the field of view into the diameter of the field of view. For example, if the diameter of the field is 5 mm and you estimate that 50 cells laid end to end would cross the diameter, then 5 mm/50 cells = 0.1mm/cell.
Cell size can be measured using an eyepiece graticule . The graticule has a ruler on it. You must find out the distance measured for each division of the graticule. You can then use the graticule to measure cells.
To calculate the field of view of microscope you need to know the eyepiece magnification, field number and objective lens. Once you have this information you can calculate the field of view of the microscope by dividing the field number by the magnification number.