WordNet

select (a team or individual player) for a game; "The Buckeyes fielded a young new quarterback for the Rose Bowl"
the space around a radiating body within which its electromagnetic oscillations can exert force on another similar body not in contact with it (同)field of force, force_field
a particular kind of commercial enterprise; "they are outstanding in their field" (同)field_of_operation, line of business
a region in which active military operations are in progress; "the army was in the field awaiting action"; "he served in the Vietnam theater for three years" (同)field of operations, theater, theater of operations, theatre, theatre of operations
the area that is visible (as through an optical instrument) (同)field of view
(computer science) a set of one or more adjacent characters comprising a unit of information
(mathematics) a set of elements such that addition and multiplication are commutative and associative and multiplication is distributive over addition and there are two elements 0 and 1; "the set of all rational numbers is a field"
a geographic region (land or sea) under which something valuable is found; "the diamond fields of South Africa"
a piece of land cleared of trees and usually enclosed; "he planted a field of wheat"
all of the horses in a particular horse race
all the competitors in a particular contest or sporting event
somewhere (away from a studio or office or library or laboratory) where practical work is done or data is collected; "anthropologists do much of their work in the field"
answer adequately or successfully; "The lawyer fielded all questions from the press"
catch or pick up (balls) in baseball or cricket
play as a fielder
secret; "keep it dark"
absence of light or illumination (同)darkness
an unenlightened state; "he was in the dark concerning their intentions"; "his lectures dispelled the darkness" (同)darkness
showing a brooding ill humor; "a dark scowl"; "the proverbially dour New England Puritan"; "a glum, hopeless shrug"; "he sat in moody silence"; "a morose and unsociable manner"; "a saturnine, almost misanthropic young genius"- Bruce Bliven; "a sour temper"; "a sullen crowd" (同)dour, glowering, glum, moody, morose, saturnine, sour, sullen
marked by difficulty of style or expression; "much that was dark is now quite clear to me"; "those who do not appreciate Kafkas work say his style is obscure" (同)obscure
(used of color) having a dark hue; "dark green"; "dark glasses"; "dark colors like wine red or navy blue"
brunet (used of hair or skin or eyes); "dark eyes"
devoid of or deficient in light or brightness; shadowed or black; "sitting in a dark corner"; "a dark day"; "dark shadows"; "dark as the inside of a black cat"
not giving performances; closed; "the theater is dark on Mondays"
magnifier of the image of small objects; "the invention of the microscope led to the discovery of the cell"

PrepTutorEJDIC

〈C〉『野原』,[牧]草地;田;畑;《the fields》田野,田畑 / 〈C〉(雪・氷などの)原,広がり / 〈C〉(鉱物などの)産出地,埋蔵地 / 〈C〉『戦場』(battlefield);戦闘(battle) / 〈C〉(スポーツの)『競技場』;(陸上のトラックに対して)フィールド / 〈C〉(ある用途の)場,地面 / 〈C〉(研究・活動などの)『分野』,領域 / 《the~》現地 / 〈C〉(電気・磁気などの)場;(レンズの)視界 / 〈C〉(絵・旗などの)地,下地 / 《the~》《集合的に》(キツネ狩り・競技の)参加者;(競馬の)出走馬;(野球の)守備選手 / (野球・クリケットで)〈打球〉‘を'さばく / 〈選手〉‘を'出場させる,守備につける / (野球・クリケットで)野手をつとめる
『暗い』やみの / (毛髪・皮膚・目の)『浅黒い』,(色の)濃い / 陰うつな,陰気な(gloomy) / 腹黒い,悪意のある(evil) / 隠した,秘密の / (意味が)明らかでない,なぞめいた / 未発の;無知の / 〈U〉《the~》『やみ』,暗がり(darkness) / 《冠詞なしで》『夜』(night);『日暮れ』(nightfall) / 〈U〉暗い色,濃い陰
『顕微鏡』
大胆な,ずぶとい(bold) / 思いきった,ざん新な / {名}〈U〉 / 大胆不敵,勇敢さ
(軽べつ・非難を表して)ええっ,まあ

Wikipedia preview

出典(authority):フリー百科事典『ウィキペディア（Wikipedia）』「2014/06/23 22:21:17」(JST)

wiki en

Dark field microscopy (dark ground microscopy) describes microscopy methods, in both light and electron microscopy, which exclude the unscattered beam from the image. As a result, the field around the specimen (i.e. where there is no specimen to scatter the beam) is generally dark.

1 Light microscopy applications
- 1.1 The light's path
- 1.2 Advantages and disadvantages
- 1.3 Use in computing
2 Transmission electron microscope applications
- 2.1 Conventional darkfield imaging
- 2.2 Weak beam imaging
- 2.3 Low and high angle annular darkfield imaging
- 2.4 Digital darkfield analysis
3 See also
4 Footnotes
5 External links

Light microscopy applications

In optical microscopy, darkfield describes an illumination technique used to enhance the contrast in unstained samples. It works by illuminating the sample with light that will not be collected by the objective lens, and thus will not form part of the image. This produces the classic appearance of a dark, almost black, background with bright objects on it.

The light's path

The steps are illustrated in the figure where an upright microscope is used.

Diagram illustrating the light path through a dark field microscope.

Light enters the microscope for illumination of the sample.
A specially sized disc, the patch stop (see figure) blocks some light from the light source, leaving an outer ring of illumination. A wide phase annulus can also be reasonably substituted at low magnification.
The condenser lens focuses the light towards the sample.
The light enters the sample. Most is directly transmitted, while some is scattered from the sample.
The scattered light enters the objective lens, while the directly transmitted light simply misses the lens and is not collected due to a direct illumination block (see figure).
Only the scattered light goes on to produce the image, while the directly transmitted light is omitted.

Advantages and disadvantages

Dark field microscopy produces an image with a dark background.

Dark field microscopy is a very simple yet effective technique and well suited for uses involving live and unstained biological samples, such as a smear from a tissue culture or individual water-borne single-celled organisms. Considering the simplicity of the setup, the quality of images obtained from this technique is impressive.

The main limitation of dark field microscopy is the low light levels seen in the final image. This means the sample must be very strongly illuminated, which can cause damage to the sample. Dark field microscopy techniques are almost entirely free of artifacts, due to the nature of the process. However the interpretation of dark field images must be done with great care as common dark features of bright field microscopy images may be invisible, and vice versa.

While the dark field image may first appear to be a negative of the bright field image, different effects are visible in each. In bright field microscopy, features are visible where either a shadow is cast on the surface by the incident light, or a part of the surface is less reflective, possibly by the presence of pits or scratches. Raised features that are too smooth to cast shadows will not appear in bright field images, but the light that reflects off the sides of the feature will be visible in the dark field images.

Comparison of transillumination techniques used to generate contrast in a sample of tissue paper. 1.559 μm/pixel (when viewed at full resolution).
Dark field illumination, sample contrast comes from light scattered by the sample.
Bright field illumination, sample contrast comes from absorbance of light in the sample.
Cross-polarized light illumination, sample contrast comes from rotation of polarized light through the sample.
Phase contrast illumination, sample contrast comes from interference of different path lengths of light through the sample.

Use in computing

Dark field microscopy has recently been used in computer mouse pointing devices, in order to allow an optical mouse to work on transparent glass by imaging microscopic flaws and dust on its surface.

Transmission electron microscope applications

Weak beam DF of strain around nuclear track cores.

Darkfield studies in transmission electron microscopy play a powerful role in the study of crystals and crystal defects, as well as in the imaging of individual atoms.

Conventional darkfield imaging

Briefly, imaging^[1] involves tilting the incident illumination until a diffracted, rather than the incident, beam passes through a small objective aperture in the objective lens back focal plane. Darkfield images, under these conditions, allow one to map the diffracted intensity coming from a single collection of diffracting planes as a function of projected position on the specimen, and as a function of specimen tilt.

In single crystal specimens, single-reflection darkfield images of a specimen tilted just off the Bragg condition allow one to "light up" only those lattice defects, like dislocations or precipitates, which bend a single set of lattice planes in their neighborhood. Analysis of intensities in such images may then be used to estimate the amount of that bending. In polycrystalline specimens, on the other hand, darkfield images serve to light up only that subset of crystals which is Bragg reflecting at a given orientation.

Animation: darkfield imaging of crystals

Digital darkfield simulation of 2nm metal particles on a nano-cylinder

This animation illustrates movement of an aperture (centered in the orange figure at left) over the power spectrum (a digital substitute for the back focal-plane's optical diffraction pattern) shown with the DC peak (or unscattered beam) below center. Only nanocrystals with projected periodicities that diffract into the aperture light up in the darkfield image at right. The aperture is moving by 1.25 degree increments around the ring associated with diffraction from gold 2.3 Ångstrom (111) lattice spacings.

Weak beam imaging

Digital darkfield of internal twins.

Weak beam imaging involves optics similar to conventional darkfield, but use of a diffracted beam harmonic rather than the diffracted beam itself. Much higher resolution of strained regions around defects can be obtained in this way.

Low and high angle annular darkfield imaging

Annular dark-field imaging requires one to form images with electrons diffracted into an annular aperture centered on, but not including, the unscattered beam. For large scattering angles in a scanning transmission electron microscope, this is sometimes called Z-contrast imaging because of the enhanced scattering from high atomic number atoms.

Digital darkfield analysis

This a mathematical technique intermediate between direct and reciprocal (Fourier-transform) space for exploring images with well-defined periodicities, like electron microscope lattice-fringe images. As with analog darkfield imaging in a transmission electron microscope, it allows one to "light up" those objects in the field of view where periodicities of interest reside. Unlike analog darkfield imaging it may also allow one to map the Fourier-phase of periodicities, and hence phase-gradients which provide quantitative information on vector lattice-strain.

Footnotes

^ P. Hirsch, A. Howie, R. Nicholson, D. W. Pashley and M. J. Whelan (1965/1977) Electron microscopy of thin crystals (Butterworths/Krieger, London/Malabar FL) ISBN 0-88275-376-2

External links

Wikimedia Commons has media related to Dark-field microscopy.

Nikon - Stereomicroscopy > Darkfield Illumination
Molecular Expressions
Darkfield Illumination Primer

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