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Topic: Numerical aperture (microscopy)

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	Olympus Microscopy Resource Center: Anatomy of the Microscope - Numerical Aperture and Resolution
		The numerical aperture of a microscope objective is a measure of its ability to gather light and resolve fine specimen detail at a fixed object distance.
		Numerical aperture determines the resolving power of an objective, but the total resolution of a microscope system is also dependent upon the numerical aperture of the substage condenser.
		As the numerical aperture and light cone angle of an objective increases however, the size of the Airy disk decreases as illustrated in Figure 4(b) and Figure 4(c).
	www.olympusmicro.com /primer/anatomy/numaperture.html (2208 words)

	Botany online: Microscopy
		Numerous statements on the refraction of light by lenses or waterfilled spheres and the resulting magnification proof, that the effects of magnification were already known in antiquity.
		The aperture of 0.95 corresponds to an angle alpha of roughly 72°.
		An increase of the numerical aperture can be achieved by the choice of a medium between objective and object with an index of refraction bigger than that of air.
	www.biologie.uni-hamburg.de /b-online/e03/03.htm (1762 words)

	Olympus FluoView Resource Center: Signal-to-Noise Considerations
		In laser scanning fluorescence confocal microscopy, of biological materials in particular, the signal levels are typically low due to the limited amount of light obtainable from the small fluorophore probe volume in the focused beam.
		The optimum operation of the confocal microscope entails attempting to balance the conflicting requirements of utilizing an aperture in front of the detector, which is responsible for imparting the beneficial aspects of the confocal configuration, against the reduction in signal that the aperture also produces.
		At aperture size less than approximately 4 optical units, beneficial confocal imaging properties are achieved with only about 1 percent of the background being admitted to the detector, at a moderate signal loss of perhaps 25 percent for specimen thickness as great as several hundred times the aperture size.
	www.olympusconfocal.com /theory/signaltonoise.html (3928 words)

	Learning about microscopy
		The numerical aperture determines the size of the cone of light transmitted through the lens--the larger the cone of light, the greater the resolving power.
		Resolving power is also dependent upon the numerical aperture of the condenser and the wavelength of the light source used.
		The numerical aperture is etched on the condenser and objective.
	www.jsu.edu /depart/biology/learning_about_microscopy.html (2888 words)

	Numerical aperture - Wikipedia, the free encyclopedia
		In optics, the numerical aperture (NA) of an optical system is a dimensionless number that characterizes the range of angles over which the system can accept or emit light.
		In microscopy, NA is important because it indicates the resolving power of a lens.
		Numerical aperture is a measure of the diameter of the aperture compared to the focal length.
	en.wikipedia.org /wiki/Numerical_aperture_(microscopy) (715 words)

	Nikon MicroscopyU: Concepts and Formulas in Microscopy: Numerical Aperture
		Numerical Aperture (also termed Object-Side Aperture) is a value (often symbolized by the abbreviation NA) originally defined by Abbe for microscope objectives and condensers.
		In the numerical aperture equation, n represents the refractive index of the medium between the objective front lens and the specimen, and
		A longitudinal slice of this cone of light reveals the angular aperture, a value that is determined by the focal length of the objective.
	www.microscopyu.com /articles/formulas/formulasna.html (460 words)

	Olympus Microscopy Resource Center: Specialized Microscopy Techniques - Laser Systems for Optical Microscopy
		The lasers commonly employed in optical microscopy are high-intensity monochromatic light sources, which are useful as tools for a variety of techniques including optical trapping, lifetime imaging studies, photobleaching recovery, and total internal reflection fluorescence.
		As an example, if a 100x objective having a numerical aperture of 1.3 (producing a focal length of approximately 1.6 millimeters) is employed to concentrate the 488-nanometer beam of an argon laser having a 0.3-millimeter radius, the focused spot radius (determined from the previous equation) is 0.8 micrometer.
		Present applications of lasers in microscopy are expanding rapidly in the areas of confocal microscopy, optical trapping, and the release of caged compounds and fluorophores.
	www.olympusmicro.com /primer/techniques/microscopylasers.html (5330 words)

	4/26/01 graduate seminar - Microscopy Beyond the Diffraction Limit: Guided and Propagating Fields
		Standard optical microscopy is not capable of obtaining a transverse resolution with a definition better than approximately half a wavelength of light due to the diffraction limit, also termed the Rayleigh or Abbe limit.
		The resolution is inversely proportional to the Numerical Aperture (NA).
		Because both the tip-to-sample separation and the tip aperture are a small fraction of the wavelength, the spatial resolution is given approximately by the tip diameter.
	www.ece.uiuc.edu /seminar/fa00/fields.html (366 words)

	Nikon MicroscopyU: Anatomy of the Microscope - Numerical Aperture Light Cones: Interactive Java Tutorial
		The light-gathering ability of a microscope objective is quantitatively expressed in terms of the numerical aperture, which is a measure of the number of highly diffracted image-forming light rays captured by the objective.
		As the angular aperture is varied with the slider, the size and shape of the illumination cone entering the objective front lens is altered.
		Theoretically, the highest angular aperture obtainable with a standard microscope objective would be 180 degrees, resulting in a value of 90 degrees for the half-angle utilized in the numerical aperture equation.
	www.microscopyu.com /tutorials/java/objectives/nuaperture/index.html (597 words)

	microscopy_lec01
		Microscopy is the science that deals with the development of microscopes.
		The greater the numerical aperture the greater the resolution.
		Numerical aperture (N.A.) - a designation, usually engraved on objectives and condensers, expressing the amount of light reaching the specimen.
	www.personal.psu.edu /faculty/w/x/wxm15/Online/Microscopy/microscopy_lec01.htm (987 words)

	Olympus FluoView Resource Center: Introduction to Confocal Microscopy
		Coherent light emitted by the laser system (excitation source) passes through a pinhole aperture that is situated in a conjugate plane (confocal) with a scanning point on the specimen and a second pinhole aperture positioned in front of the detector (a photomultiplier tube).
		In traditional widefield epi-fluorescence microscopy, the entire specimen is subjected to intense illumination from an incoherent mercury or xenon arc-discharge lamp, and the resulting image of secondary fluorescence emission can be viewed directly in the eyepieces or projected onto the surface of an electronic array detector or traditional film plane.
		Several apertures of varying diameter are usually contained on a rotating turret that enables the operator to adjust pinhole size (and optical section thickness).
	www.olympusconfocal.com /theory/confocalintro.html (4303 words)

	Advanced Light Microscopy and Image Analysis Core (Site not responding. Last check: 2007-10-16)
		A new technique in light microscopy using a pulse from a focused light source, often a laser microbeam to deplete the fluorescence in a local region in a living cell.
		The subsequent recovery of fluorescence in the irradiated region is measured to establish the mobility of the molecules that carry the fluorescent tag.
		The numerical aperture is a measure of the light gathering capacity of the lens system and determines its resolving power and depth of field.
	www.wadsworth.org /cores/alm/glossary.htm (2652 words)

	microscopy.lecture2
		In dark field microscopy, only the cells are illuminated, not the background (by using light at such an angle that the only light that goes into the objective comes from scattering off the cells).
		Fluorescence microscopy takes advantage of the fact that some compounds emit light of a different wavelength when a light is shown on them.
		One of the limits to the resolution of light microscopy is the wavelength of light.
	oregonstate.edu /instruct/mb302/field/Lecture3.htm (322 words)

	Imperial College London \| (Site not responding. Last check: 2007-10-16)
		numerical aperture lenses is arguably one of the most important events to occur in optics during the last century.
		The given numerical method determines the field which is scattered by the specimen.
		Amplitude microscopy methods are ineffective in the analysis of such objects since the eye, CCD cameras, photomultipliers and other such light detection devices are sensitive only to variations in intensity and not phase.
	www.imperial.ac.uk /research/photonics/pt_group/peter_torok_research_topics_OIM.htm (2291 words)

	Near-Field Microscopy (Site not responding. Last check: 2007-10-16)
		By illuminating the backside of the screen with a high-intensity light source, light passing through the aperture would be confined by the dimensions of the hole.
		The difficulties in aperture formation, illumination, and sample manipulation were all recognized as hurdles that would have to be overcome.
		To form an aperture, the sides of the probe must be coated with an opaque metal to confine the light.
	www.chem.ku.edu /rdunngroup/new_page_6.htm (2273 words)

	Brain Research Institute (Site not responding. Last check: 2007-10-16)
		The numerical aperture number is directly related to the cone of light from the specimen at its vertex which is brought into the lens.
		The bigger a cone of light that can be brought into the lens, the higher its numerical aperture is. Therefore the higher the numerical aperture of a lens, the better the resolution of a specimen will be which can be obtained with that lens.
		The second advantage of using a higher numerical aperture is that since more orders of diffraction from the object are brought into the lens, more light generally is brought into a higher numerical aperture lens producing brighter images.
	www.bri.ucla.edu /bri_research/microscopy_numap_reso.asp (883 words)

	Molecular Expressions Microscopy Primer: Frequently Asked Questions (Site not responding. Last check: 2007-10-16)
		The higher the numerical aperture, other things being equal, the better the objective is able to separate the details of the specimen in forming an image; also the brighter the image.
		Resolving power is related to the numerical aperture of the objective; the higher the numerical aperture, the better the resolving power.
		The general rule of thumb in microscopy is that the total magnification should probably not exceed 750x to 1000x the numerical aperture.
	molecular.magnet.fsu.edu /primer/faq.html (3508 words)

	Microscopy - Wikipedia, the free encyclopedia
		Ultrasonic Force Microscopy (UFM) has been developed in order to improve the details and image contrast on "flat" areas of interest where the AFM images are limited in contrast.
		Ultrasonic force microscopy allows the local mapping of elasticity in atomic force microscopy by the application of ultrasonic vibration to the cantilever or sample.
		In an attempt to analyse the results of ultrasonic force microscopy in a quantitative fashion, a force-distance curve measurement is done with ultrasonic vibration applied to the cantilever base, and the results are compared with a model of the cantilever dynamics and tip-sample interaction based on the finite-difference technique.
	en.wikipedia.org /wiki/Microscopy (2666 words)

	Optical Microscopy - Visablity
		Reducing the numerical aperture of the system, usually by closing down the condenser aperture diaphragm, increases contrast in the image, but reduces resolution.
		These include atomic force microscopy, in which the probe touches the surface and is moved up or down to follow the topography; thermal force microscopy, measuring surface temperature; lateral force microscopy, measuring friction; magnetic force microscopy, measuring magnetic fields; and electrostatic force microscopy, measuring charge density.
		Scanning electron microscopy moves a fine beam of electrons back and forth across the, measuring back-scattered electrons, current in the object, etc. The electron microprobe is essentially a scanning electron microscope designed to produce and measure characteristic X-rays from the sample.
	www.dyerlabs.com /microscopy/visability.html (1267 words)

	Two-Photon Microscopy
		Multi-photon fluorescence microscopy in cell biology uses pulsed lasers (pulse width in the range of 20 fs to 5 ps, typically ~ 100 fs) with high repetition rates (10 -100 MHz).
		The development of these dyes took place during the last three decades and was based on applications in the fields of classical microscopy using near UV and visible light sources.
		Fluorescence microscopy ased on three- or more-photon absorption using the Ti:Sapphire laser for excitation would excite far-UV absorbing fluorophores that are not very well characterised and rarely used.
	www.fz-juelich.de /ibi/ibi-1/Two-Photon_Microscopy (848 words)

	oe magazine - Special Focus: Microscopy in Multiples (Site not responding. Last check: 2007-10-16)
		The tradeoff between FOV and resolution becomes acutely apparent in medical microscopy systems, with which there is often a need to image relatively large areas of a microscope slide at high resolution.
		One challenge in the realization of array microscopy is the fabrication of large numbers of identical lenses with characteristics that are sufficiently well matched to allow simultaneous imaging of the object at the same conjugates and without variation of imaging performance across the array.
		To solve this problem, we suspended the optical array with the detector and relevant electronics on a scanner platform with the ability to change not only the optic-to-sample distance (z-direction), as is the case with conventional microscopes, but also pitch and roll.
	oemagazine.com /fromTheMagazine/may05/microscopy.html (1827 words)

	Advanced Electron Microscopy & Imaging
		The purpose of the eyepieces in a light microscope is to further enlarge the primary image formed by the objective lens and to render it visible as a "virtual" image for the eye to see.
		Open up the aperture of the field diaphragm until its diameter is equal to or just less than the observed field in the microscope.
		A mask is then positioned behind the objective lens in the aperture plane, where the annular light source comes to focus.
	www.hei.org /research/aemi/lm.htm (2829 words)

	Microscopy Primer: Chapter 4. Basic microscopy.
		Check the aperture: only the center will be illuminated, because the numerical aperture of the objective is now much higher than before.
		Adjust the iris until about 85% of the 20x or 40x objective aperture is illuminated, the image should be nice.
		The centering telescope of a phase-contrast set is very convenient for checking the aperture as the image is then larger and can be sharply focused by turning the top lens.
	www.microscopy-uk.org.uk /primer/basics.htm (2226 words)

	Optical Microscopy
		An important advance that was critical for the modern use of optical microscopy in cell biology was the development of phase contrast techniques.
		In conventional ("bright field") microscopy, an enlarged image of the sample is formed by the microscope objective, and this image is then viewed using the eyepiece.
		Microscopy of any kind is limited by the wave nature of the probing particles.
	www.columbia.edu /~leonard/BMELab/Optics.html (2724 words)

	Confocal Scanning Microscopy
		Confocal Microscopy also is advantageous because it allows the user to view different parts of the specimen when rotating the focus knob without loosing view of the specimen.
		Also another use of confocal microscopy is viewing a fixed tissue that has been stained with a flourescently labeled antibody because immunoflourescence stains are highly sensitive because antigen expressing cells can be readily detected against a dark non-fluorescent background (Epstein, 366).
		The Leica Company also explains that the depth of the focal plane is the wavelength of light and the numerical aperture of the objective used and the diameter of the diaphragm determine it.
	www.samford.edu /~gekeller/stephens.html (660 words)

	Principles of Light Microscopy
		N.A. (Numerical Aperture) is a mathematical calculation of the light-gathering capabilities of a lens.
		In practice, at full aperture and with good oil immersion lenses (N.A. 1.4 for both the condenser and the objective) it is possible to be able to resolve slightly better than 0.2 µm.
		When the microscope is properly illuminated, both the object and the edges of the field aperture diaphragm should be in the same plane of focus and the field iris diaphragm should be centered in the field of view.
	www.life.umd.edu /cbmg/faculty/wolniak/wolniakmicro.html (4372 words)

	Biology 750: Electron Microscopy
		is the aperture half angle of the objective lens.
		In light microscopy this would be accomplished with an annular phase plate in the diffraction plane of the objective lens; this is not very practical in electron microscopy.
		This is certainly the most efficient geometry for darkfield electron microscopy since the annular detector can be designed to collect virtually all of the elastically scattered electrons and can also exclude almost all inelastically scattered electrons which degrade CTEM images by increasing chromatic aberration.
	www.sci.sdsu.edu /TFrey/Bio750/ElecMicroscopy.html (4159 words)

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