Microscopy

Light microscope

A light microscope uses visible light, an eyepiece lens and objective lens to view a specimen. Resolution 200nm. Magnification x1500- x2000.

Transmission electron microscope (TEM)

A beam of electrons is transmitted through a specimen and focused to produce an image (2D). Resolution 0.2-0.5nm. Magnification x500,000- x 2,000,000

Scanning electron microscope (SEM)

A beam of electrons is sent across the surface of a specimen and the reflected electrons are collected (3D). Resolution 3-10nm. Magnification x100,000- x500,000

Magnification

How many times larger the image is than the actual size of the object being viewed

Resolution

The degree to which you can distinguish two separate points

Magnification equation

Size of image/Actual size

How to calibrate an eyepiece graticule

Step 1- Line up the stage micrometre and eyepiece graticule whilst looking through the eyepiece

Step 2- Count how many divisions on the eyepiece graticule fit into one division on the micrometre scale

Step 3- Each division on the micrometre could be 10um for example, so this can be used to calculate one division on the eyepiece graticule.

How do you measure diameter of a cell on a microscope

1. use eyepiece graticule

2. calibrate graticule, using stage micrometre calculate the length of one epu

3. measure the diameter of the nucleus in, epu graticule units

4. take repeat measurements and calculate a mean diameter (in epu)

5. use calibrated epu to calculate diameter (of nucleus) (in μm) / described