Ocular micrometer

Not to be confused with micrometre or Micrometer (device).

For the chemical unit "μM", see Micromolar.

An ocular micrometer or eyepiece micrometer is a glass disk, engraved with a ruled scale, that fits in an eyepiece of a microscope,^[1][2] which is used to measure the size of microscopic objects through magnification under a microscope. When the eyepiece micrometer is calibrated using a stage micrometer, the length of the divisions on the scale depends on the degree of magnification.^[3]

An Ocular micrometer

Microscopic Field showing an Ocular Micrometer scale

Stage Micrometer used in microscopic calibration

Ocular micrometer

Micrometer Eyepiece

Stage micrometer divisions as seen under microscope. It is used to calibrate the ocular micrometer. Smallest division = 0.01mm or 10 microns.

See Also

• Camera Lucida;
• Reticle
• Hemocytometer