Microscope Calibration: a short tutorial [New version]

Summary

This tutorial explains how to calibrate an ocular micrometer for accurate measurements in microscopy. The video first introduces the concept of an ocular micrometer and explains its importance, particularly when working with small specimens. It walks viewers through the process of calibration using a stage micrometer, comparing ocular units with known physical lengths. The tutorial covers the logic behind calibration, provides practical examples, and emphasizes that calibration must be done for each objective lens on the microscope. The video concludes by highlighting the importance of recording calibration results for future reference.

Takeaways

• 😀 Ocular micrometers are embedded rulers in the eyepiece of a microscope, used to measure specimens too small for a regular ruler.
• 😀 Calibration of the ocular micrometer is necessary because ocular units (OU) do not correspond to physical measurements without it.
• 😀 The size of an ocular unit changes with the magnification level, meaning measurements are magnification-dependent.
• 😀 A stage micrometer, with a known length (usually 1mm or 1000 microns), is used for calibration of the ocular micrometer.
• 😀 To calibrate, compare the known length of the stage micrometer to the ocular units seen through the microscope.
• 😀 Once calibration is complete, one ocular unit (OU) can be converted into an absolute measurement in microns (e.g., 1 OU = 99 microns at 10x magnification).
• 😀 Calibration results will differ depending on the magnification objective lens (e.g., 60x objective lens calibration = 17 microns per OU).
• 😀 Always calibrate the ocular micrometer for each objective lens, as measurements vary depending on the magnification used.
• 😀 Record the calibration factor for each objective lens in a lab notebook to ensure accurate and consistent measurements in future experiments.
• 😀 The ocular micrometer calibration process is essential for precise measurements of small specimens in laboratory settings, ensuring scientific accuracy.

Q & A

What is an ocular micrometer?

An ocular micrometer is an embedded ruler within one of the eyepieces of a microscope, used to measure specimens under a microscope. It does not provide physical measurements until calibrated.

Why is calibration necessary for an ocular micrometer?

Calibration is necessary because the ocular micrometer's measurements depend on the magnification used. Without calibration, it cannot provide accurate physical dimensions of specimens.

What problem does the ocular micrometer solve?

The ocular micrometer solves the problem of measuring very small specimens that cannot be measured using a regular ruler on the microscope stage.

How does the ocular micrometer measurement vary with magnification?

The ocular micrometer's reading changes with different objective lenses. For example, a specimen that measures 2 ocular units at 10x magnification might measure 8 ocular units at 40x magnification, even though the physical specimen size hasn’t changed.

How do you calibrate an ocular micrometer?

Calibration involves comparing the ocular micrometer's measurements with a known reference, such as a stage micrometer, which has a known length. By comparing the two, you can convert ocular units into physical measurements like microns.

What is a stage micrometer and how is it used in calibration?

A stage micrometer is a slide with a known length, usually in millimeters, placed on the microscope stage. It serves as a reference for comparing the ocular micrometer's scale to determine the length of an ocular unit.

What is the relationship between stage units (SU) and ocular units (OU)?

Stage units (SU) represent the separation between two major lines on the stage micrometer, while ocular units (OU) represent the separation between major lines on the ocular micrometer. Calibration compares these units to convert ocular units into known physical lengths.

What is the length of one ocular unit when using the 10x objective lens?

When using the 10x objective lens, one ocular unit is equal to 99 microns, as determined through calibration with a stage micrometer.

How do you calculate the length of a specimen using the ocular micrometer?

Once calibrated, you can multiply the number of ocular units measured by the ocular micrometer by the known length of one ocular unit. For example, if a specimen measures 2 ocular units, it would be 198 microns long (2 x 99 microns).

What should you do if you change the objective lens of your microscope?

You should recalibrate the ocular micrometer for each objective lens you use because each objective lens provides a different field of view, affecting the scale of the ocular micrometer.