Ocular Micrometer Calibration: Why It's Objective-Specific

The calibration factor for an ocular micrometer is unique to each objective combination because:

• Objective magnification is fixed (marked on the lens).
• Image size from the ocular micrometer varies with the distance between the micrometer and eyepiece.

Increasing that distance shrinks the micrometer image; decreasing it enlarges the image. Thus, the calibration factor must account for both objective magnification and the specific image size produced.

Example

• 10× objective + micrometer factor 0.1 mm → each division = 0.1 mm in specimen.
• 20× objective + same micrometer → each division = 0.05 mm.

Always use the factor calibrated for the exact objective in use to ensure accurate measurements.