What Is the Depth of Field in Microscopy?

In microscopy, the depth of field refers to the range of distance that runs parallel to the optical axis where the specimen can move and still be viewed without negatively affecting the clarity of the object under observation. The depth of field determines the vertical extent of the plane of focus, which is typically measured in microns.

In various scientific fields, a microscope is an important tool in viewing and examining objects that are too small to be seen by the naked eye. One of the basic components of a microscope is an eyepiece or ocular lens. A nosepiece, which has several objective lenses is located below the eyepiece. The objective lenses are calibrated into different levels of magnification. Depending on what magnification the specimen is to be viewed, the nosepiece can be easily rotated and the objective lens set into place. Other parts include a mechanical stage, substage condenser, iris diaphragm, substage illuminator, a rheostat and two knobs that are adjusted to focus the sample specimen.

When viewing an object, the overall magnification is calculated by multiplying the value of the ocular lenses with the value of the objective lenses. The total magnification is indirectly proportional to the depth of field. As magnification increases, the axial resolving power of an objective, which is the depth of field, is reduced.