# depth of focus

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## fo·cal depth

, depth of focus
the greatest distance through which an object point can be moved while maintaining a clear image.
Synonym(s): penetration (3)

## fo·cal depth

, depth of focus (fō'kăl depth, fō'kŭs)
The greatest distance through which an object point can be moved while remaining in focus.

## depth of focus

For a given setting of an optical system (or a steady state of accommodation of the eye) it is the distance in front and behind the focal point (or retina) over which the image may be focused without causing a sharpness reduction beyond a certain tolerable amount. (The criterion could be as much as a line of letters on a Snellen chart.) The depth of focus D is represented by the total distance in front and behind (Fig. D1). As with depth of field, it is inversely proportional to the diameter of the diaphragm (or pupil). It can be calculated, expressed in dioptres, using the equation
D = (2b/p)Fe
where Fe is the power of the emmetropic eye, p the pupillary diameter and b the maximum size of the retinal image beyond which it is perceived as blurred. Example: Assuming a pupil of 3 mm and a retinal image spread over five cones, each 0.002 mm in diameter and spaces between the cones of 0.0005 mm, that is a total size = 0.012 mm, D = 2 ✕ 0.012/3 ✕ 60 = 0.48 D. Thus an object appears clear if the vergence at the eye varies in the range ±0.24 D. If the eye is focused at infinity, the equation becomes D = (b/p) Fe.
Fig. D1 Schematic representation of the depth of field and the depth of focus of an eye fixating an object at O (I, retinal image size corresponding to the tolerable resolution)

## fo·cal depth

, depth of focus (fō'kăl depth, fō'kŭs)
The greatest distance through which a point can move in focus.
References in periodicals archive ?
Juthani, "Extended depth of focus intraocular lenses for presbyopia," Current Opinion in Ophthalmology, vol.
Nevertheless, it is not to say that such a lens will not have any depth of focus at all.
By basing units or curricula on concepts, educators are able to increase the thought level and provide a depth of focus on subjects traditionally "covered." If, for example, the library media specialist helps the teachers identify "risk taking" as a concept, then the westward movement can be studied in terms of risk taking.
While you are wearing the pinhole glasses, they may briefly improve visual acuity, because the pinholes permit only light rays coming straight into the eye to hit the retina, so that depth of focus is improved.
At the moment, however, their holograms appear two-dimensional because the depth of focus is about the same as the thickness of their sample.
Phivolcs said the quake was of tectonic origin, and had a 14-kilometer depth of focus.
Mark'ennovy highlighted its contact lens for presbyopia, which includes extended depth of focus (EDOF) technology from the Brien Holden Vision Institute.
Our Bessel focus lenses in particular, enable our customers to engineer beams with elongated depth of focus that greatly improve the efficiency of their laser processing heads.
EDOF IOLs (extended depth of focus IOLs) may be considered as a new generation of IOLs.
It was tectonic in origin and had a depth of focus of focus of 126 kilometers.
It takes advantage of the short UV wavelength to provide a small spot size and a large depth of focus. UV lasers also take advantage of the cold marking process not requiring high average powers and allowing damage free marking on many materials.

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