This IBDP Biology blog post will look into the practical processes and the equations needed for magnification, let's get to it!
Use of a light microscope to investigate the structure of cells and tissues, with drawing of cells.
Calculation of the magnification of drawings and the actual size of structures and ultrastructures shown in drawings of micrographs.
Equations
magnification of a microscope = mag. eyepiece lens x mag. objective lens
actual size = (length of image/length of scale bar)*value scale bar represents
magnification = size of image / actual size of specimen
magnification using scale bar = size of scale bar / what scale bar represents
1cm = 10mm = 10,000 um
Be sure to use the same units.
How to calibrate an eyepiece graticule
- When carrying out calibration, each objective lens has to be separately calibrated. This will result in separate calibration factors for each objective.
- Start with the lowest power objective on the microscope.
- The scale on the stage micrometer is aligned with the scale of the eyepiece graticule and then a reading is taken from the scales.
These readings are then used to calculate the calibration factor for the objective lens in use. The following example shows how to calibrate thegraticule for the x40 objective lens:
Reading from the two scales we find 100 divisions on the eyepiece graticule equals 25.9 divisions on the stage micrometer.
- For the particular stage micrometer we are using 100 divisions = 1mm (this information is marked on the stage micrometer).
- Each division is 1/100 mm = 10µm
That is all for the magnification practical!
