Magnification
Equation
Magnification can be worked out from a photograph or drawing using the equation
below:
The same unit of measurement should be used when making the calculation - metre
(m), millimetre (mm) or micrometre (µm).
To convert millimetres into micrometres, multiply by 1000.
The above equation can be rearranged in order to calculate the actual length of the
cell and the magnification used as well as the length of the image.
Actual Length = length of the Image divided by the Magnification.
Magnification = length of the Image divided by the Actual Length.
Scale bar
Magnification can be calculated using a scale bar. This is a line drawn near the
photograph or drawing which has a label showing the actual length of the bar before
being magnified.
Working out magnification:
1. Measure the scale bar image (beside drawing) in mm.
2. Convert to µm (multiply by 1000).
3. Magnification = scale bar image divided by actual scale bar
length (written on the scale bar).
Electron microscopes
Continually increasing the magnification past a certain point does not increase
the detail visible in an image.
The most important property of a microscope is its resolution - the ability to
show detail.
The best light microscope can show details that are 0.2µm apart and need a
magnification of roughly x1500 so that our eyes can see it - this allows us to see
larger cell structures.
Electron microscopes pass beams of electrons through a specimen and have a
much greater resolution than a light microscope.
Their resolution can show details that are 0.0001µm apart - allowing us to clearly see
inside the parts of a cell e.g. inside a chloroplast or mitochondrion.
Using a light microscope
1.
When using a light microscope it’s important to start with the low power objective lens
as the field of view will be wider, increasing the number of cells you are able to see.
This makes it easier to find what you’re looking for.
Then, ensuring the cells are in the middle of the field of view, rotate a higher powered
lens into place and begin to focus to view the cells in more detail.
Extra care is needed here because the high-powered lens can become damaged as it’s
very close to the slide