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)

Farlex Partner Medical Dictionary © Farlex 2012

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.

Medical Dictionary for the Health Professions and Nursing © Farlex 2012

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)F_e

where F_e 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) F_e.

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.

Medical Dictionary for the Dental Professions © Farlex 2012

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References in periodicals archive

Juthani, "Extended depth of focus intraocular lenses for presbyopia," Current Opinion in Ophthalmology, vol.

Monocular Clinical Outcomes and Range of Near Vision following Cataract Surgery with Implantation of an Extended Depth of Focus Intraocular Lens

Nevertheless, it is not to say that such a lens will not have any depth of focus at all.

Covered image of superlens

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.

And now, aerobic eye workouts

At the moment, however, their holograms appear two-dimensional because the depth of focus is about the same as the thickness of their sample.

Hologram: new dimensions for X-rays

Phivolcs said the quake was of tectonic origin, and had a 14-kilometer depth of focus.

Magnitude 4.1 earthquake rocks Itbayat, Batanes

Mark'ennovy highlighted its contact lens for presbyopia, which includes extended depth of focus (EDOF) technology from the Brien Holden Vision Institute.

Wearer experience

EDOF IOLs (extended depth of focus IOLs) may be considered as a new generation of IOLs.

In Vitro Aberrometric Assessment of a Multifocal Intraocular Lens and Two Extended Depth of Focus IOLs

It was tectonic in origin and had a depth of focus of focus of 126 kilometers.

Mindanao, Luzon rocked by 7 quakes in 30 hours

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.

AMS Technologies Presents New UV Laser Marking System at LASER World of PHOTONICS 2011