BOT-712 Advanced Cell Biology 3(2-1)
Estimating Size Under a Microscope
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Compound-light microscope with low and high power settings
Clear ruler with a cm/mm scale
Compass
Paper
Pencil
1. Begin sizing the microscope's viewing field at 40 times magnification.
2. Set the clear ruler into the line of view; it will measure the view field at
approximately 4 to 5 millimeters.
3. Set at low power, 100 times, it can be estimated at about 2 to 3 millimeters. Convert
this measurement to microns; the view at 100 times can be estimated at 2,000 to 3,000
microns. You can estimate anything you want to measure at low power in this range -based on how much of the field it covers -- if you keep the ruler as a measurement
grid on the left of the image.
4. Record the magnification, diameter of the circle/field of view, the number of cells that
stretch across that diameter, and finally the estimated length of one cell. Figuring the
length of this one cell is the object of your measuring exercise.
5. Divide the number of cells in view with the diameter of the field of view to figure the
estimated length of the cell. If the number of cells is 50 and the diameter you are
observing is 5 millimeters in length, then one cell is 0.1-millimeter-long. Measured in
microns, the cell would be 1,000 microns in length. The mathematical formula is D/E
= L, where D is the diameter of the viewing field, E is the estimated number of cells,
and L is the length of the cell.
Cell Sizes