# 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 ?
This, as with the limitations of the depth of focus, becomes dramatically worse as one increases the magnification in order to achieve better resolution.
More conversions are expected as customers consider to take advantage of increased depth of focus latitude for 65-nm applications now that immersion processes are becoming mature enough for production deployment.
Its extremely low downforce is unsurpassed for polishing sensitive low k dielectric films, while its superior planarization capability helps extend the use of existing dry lithography tools through the 45nm generation by increasing the depth of focus process window.
The technology increases the yield of chips per wafer through improved depth of focus, CD uniformity and other key lithography features.
POLANO improves image contrast by 20 percent, resulting in superior resolution, increased depth of focus, and improved critical dimension (CD) uniformity.
Fujinon, a sister company to Fujifilm USA, will also showcase the next generation of Precision Focus Assist, a built-in feature addressing the precise focus needs for HDTV production due to the shallow depth of focus of HD and lack of size and resolution in camera viewfinders.
The yield-related depth of focus of the immersion scanner is almost twice that of the dry scanner.
The problem with ultra-close-up photography is keeping sharp depth of focus, because the lens is very close to the subject.
Immersion lithography differs from conventional "dry" lithography in that the air between the wafer and the lens is replaced with water to improve depth of focus and extend wavelengths to lower nodes.
POLANO improves image contrast by 20 percent, resulting in superior resolution, depth of focus, and critical dimension (CD) uniformity.

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