Measurement Terms

Depth of Focus

What is "Depth of Focus"

• Depth of focus refers to the range within which the optics or image sensor can move while still maintaining a sharp image. Not to be confused with depth of field, which refers to the range that appears in focus without moving the sensor.(Figure 1)
• Also known as D.O.F. (Depth of Focus)
• In general, the higher the magnification of the objective lens, the shallower the depth of focus.
• Because the human eye adjusts differently from person to person, the perceived depth of focus varies from person to person.

Figure 1

Impact of Depth of Focus

A deep depth of focus offers several benefits:

• Simplified focus operation makes it easier to achieve and maintain focus.
• Uniform observation of minute steps allow small steps to appear as a single plane.

However, when measuring height or steps based on focus position, errors may occur, particularly when high-power lenses are used. 

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