Measuring with a Microscope Reticle

Measuring with the microscope is simple when you understand a few steps to take before using your microscope eyepiece reticle. Prior to making any measurements you will want to calibrate your microscope with a stage micrometer. An eyepiece reticle is a small piece of glass with a ruler or grid imposed on it that fits into the microscope eyepiece. When looking through the microscope, the reticle image is imposed upon your specimen image. Most often the reticle is used to make measurements or count particles.

Reticle Ruler
When using a microscope eyepiece reticle with different objective lenses, the distance between the lines on the reticle changes. In order to determine the distance between the lines on the reticle you are using, you will want to use this formula for calculation:
Reticle Division / Objective Lens Value = Distance between lines on reticle at this objective value

For example:
If you are using a 5mm reticle with 100 divisions, your reticle division is 5/100 = 0.05mm
If you want to determine the distance between lines using the 4x objective the formula is:
0.05mm / 4 = 0.0125mm when using the 4x objective.

You need to make this calculation for each objective lens used. Let's determine a few more using the same reticle example as shown above, but with the 10x, 40x and 100x objectives.

Using the 10x objective the formula looks like this:
0.05mm / 10 = 0.005mm when using the 10x objective.

Using the 40x objective the formula looks like this:
0.05mm / 40 = 0.00125mm when using the 40x objective.

Using the 100x objective the formula looks like this:
0.05mm / 100 = 0.0005mm (or 0.5um) when using the 100x objective.