Light microscopes use visible light and a combination of lenses to magnify images of mounted specimens

• Most light microscopes include both an ocular lens (~10×) and objective lens (~10×; 40×; 100×)

Using a Light Microscope

When using a light microscope to view biological specimens, the following conventions should be followed:

• The image should initially be resolved at the lowest magnification using the coarse focus mechanism
  

• Higher magnifications are then obtained by changing the objective lens (via the revolving nosepiece) and making fine focus adjustments

• The total magnification of the image is calculated by multiplying the magnification of both lenses (ocular and objective) together

• If the eyepiece has a measurement scale on its surface (eyepiece graticule), this can be used to determine sizes of biological structures

Light Microscope Components

Calculating Magnification

To calculate the linear magnification of a drawing or image, the following equation should be used:

• Magnification = Image size (with ruler) ÷ Actual size (according to scale bar)
  

In order to calculate magnification, both image size and actual size must be in the same units

• Metric conversions can be applied according to the following table:
  

• Unit

  Metre

  Centi-

  Milli-

  Micro-

  Nano-

• Sign

  m

  cm

  mm

  μm

  nm

• Size

  1 (100)

  10–2

  10–3

  10–6

  10–9

• Unit

  Sign

  Size

• Metre

  m

  1 (100)

• Centi-

  cm

  10–2

• Milli-

  mm

  10–3

• Micro-

  μm

  10–6

• Nano-

  nm

  10–9

Example Calculation