What does defocus mean?
Defocus is a transitive verb meaning to make an image, lens, or other optical system lose focus and become blurred. Its most familiar use is in photography, where a subject or background may be deliberately defocused to create shallow depth of field, soften an image, or produce a dreamy effect. The term is also used in optics and microscopy when a change in focus is intentional or technically required. Defocus is more specific than the general verb 'blur': it identifies a loss of sharpness associated with focus rather than an image being smeared by movement, low resolution, or another cause. In ordinary discussion, people may say that a camera or photograph is 'out of focus' or 'blurred'; 'defocus' is the more technical verb for causing that condition. Its specialized character makes it useful in technical and creative contexts while keeping it noticeably less common in everyday speech.
verbTo cause an image, lens, or optical system to lose focus and become blurred.
- To cause something, especially an image or optical system, to lose focus and become blurred.
"The photographer deliberately defocused the lens to give the portrait a soft, dreamlike quality."
"A shallow depth of field can defocus the background while keeping the subject sharp."
"The engineer adjusted the optics to defocus the beam and reduce unwanted interference."
Defocus turns a camera's sharp eye into a deliberate blur, making softness an artistic choice rather than merely a mistake.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Where does defocus come from?
The word was formed in the twentieth century by combining the prefix de-, meaning away from or the reversal of an action, with focus. Focus had been borrowed from Latin focus, 'hearth, fire,' before being applied to optics and the point at which rays appear to meet. Words such as focal, confocal, and refocus developed within the same modern focus-based family.
Related word forms
How defocus is actually used
Chiefly technical, especially in photography, optics, and microscopy. It is less common in general conversation than the broader verb 'blur' and often carries the implication that the loss of focus is deliberate.
Easily confused with defocus
Defocus concerns loss of optical sharpness, whereas defuse means to make a dangerous situation or device safe.