Cell structure
Living things are all made up of cells, but most cells are so small you can only see them using a microscope. It is important to grasp the units used for such tiny specimens before you start to look at them.
electron microscope
The invention of the electron microscope in the 1930s allowed biologists to see and understand more about the subcellular structures inside cells. These instruments use a beam of electrons to form an image and can magnify objects up to around 2000 000 times. Transmission electron microscopes give 2D images with very high magnification and resolution. Scanning electron microscopes give dramatic 3D images but lower magnifications. Electron microscopes are large, very expensive, and have to be kept in special temperature, pressure, and humidity-controlled rooms.
Calculating magnification
You can calculate the magnification you are using with a light microscope very simply. You multiply the magnification of the eyepiece lens by the magnification of the objective lens. So if your eyepiece lens is x4 and your objective lens is x10, your overall magnification is: 4x10=x40.
Calculating the size of an object
You will want to calculate the size of objects under the microscope. There is a simple formula for this, based on the magnification triangle. As long as you know or can measure two of the factors, you can find the third.
Magnifying and resolving power
Microscopes are useful because they magnify things, making them look bigger. The height of an average person magnified by one of the best light microscopes would look about 3.5 km, and by an electron microscope about 3500 km. There is, however, a minimum distance between two objects when you can see them clearly as two separate things. If they are closer together than this, they appear as one object. Resolution is the ability to distinguish between two separate points and it is the resolving power of a microscope that affects how much detail it can show.
Light microscopes
Light microscopes magnify up to about X2000, and have a resolving power of about 200 nm.
Electron microscopes
Electron microscopes magnify up to about ×2 000 000, and have a resolving power of around 0.2 mm.
