For outdoor signs and displays, acrylic, with its outstanding optical characteristics, weather resistance and formability, strongly dominates the picture.

For the further discussion, we shall thus assume an electron optical resolution of 80 Af and phosphor screen resolution of 60 Af.

For general computer use access technology such as screen readers, screen magnifiers and refreshable Braille displays has been widely taken up along with standalone reading aids that integrate a scanner, optical character recognition ( OCR ) software, and speech software in a single machine.

For example, the SEA-ME-WE 3 optical submarine telecommunications cable lands at both Medan and Jakarta connecting Europe with South eastern Asia ( several countries up to Japan ) and Australia ( Perth ).

For real, passive, optical systems, the output luminance is at most equal to the input.

For similar reasons, a bodyguard with a holster-carried, concealed weapon is typically not able to mount accessories onto the weapon, such as optical sights or forward handgrips.

For example, the Giant Magellan Telescope will have seven 8. 4 meter primary mirrors, with the resolving power equivalent to a optical aperture.

For example, the stability of bulk matter ( which consists of atoms and molecules which would quickly collapse under electric forces alone ), the rigidity of solids, and the mechanical, thermal, chemical, optical and magnetic properties of matter are all results of the interaction of electric charges under the rules of quantum mechanics.

For optical applications, this is characterized by the index of refraction.

For many materials ( for instance, semiconductors ), electrons move quickly from a high energy level to a meta-stable level via small nonradiative transitions and then make the final move down to the bottom level via an optical or radiative transition.

For example, the term subwavelength-diameter optical fibre means an optical fibre whose diameter is less than the wavelength of light propagating through it.

For planetary rings, the optical depth is the proportion of light blocked by the ring when it lies between the source and the observer.

* For an optical cavity consisting of two mirrors, confocal means that they share their foci.

For the optical regime, see beam divergence.

For a single-mode optical fiber, the cutoff wavelength is the wavelength at which the normalized frequency is approximately equal to 2. 405.

For an optical fiber, the effective mode volume is the square of the product of the diameter of the near-field pattern and the sine of the radiation angle of the far-field pattern.

For both families, the lowest-order solution describes a Gaussian beam, while higher-order solutions describe higher-order transverse modes in an optical resonator.

: Note: For optical fiber dispersion measurement purposes, the quantity of interest is group delay per unit length, which is the reciprocal of the group velocity of a particular mode.

For a Gaussian intensity ( i. e. power density, W / m < sup > 2 </ sup >) distribution in a single-mode optical fiber, the mode field diameter is that at which the electric and magnetic field strengths are reduced to 1 / e of their maximum values, i. e., the diameter at which power density is reduced to 1 / e < sup > 2 </ sup > of the maximum power density, because the power density is proportional to the square of the field strength.

For an optical fiber, the optical axis is along the center of the fiber core, and is also known as the fiber axis.

For example, using a long pulse length, it may possible to measure attenuation over a distance of more than 100 km, however in this case an optical event may appear to be over 1 km long.

For optical fibers, a power-law index profile is an index of refraction profile characterized by

For an optical fiber or waveguide, a radiation mode or unbound mode is a mode which is not confined by the fiber core.

For example, GOTO telescopes tend to be faster for locating items of interest than star hopping, allowing more time for studying of the object.

For example, X-ray astronomy is nearly impossible when done from the Earth, and has reached its current importance in astronomy only due to orbiting X-ray telescopes such as the Chandra observatory and the XMM-Newton observatory.

For example, the Very Large Array ( VLA ) near Socorro, New Mexico has 27 telescopes with 351 independent baselines at once, which achieves a resolution of 0. 2 arc seconds at 3 cm wavelengths.

For example, this could result in extremely long telescopes such as the very long aerial telescopes of the 17th century.

For this reason, most infrared telescopes are built in very dry places at high altitude, so that they are above most of the water vapor in the atmosphere.

For example, by far the most common molecule in the universe is H < sub > 2 </ sub > ( hydrogen gas ), but it does not have a dipole moment, so it is invisible to radio telescopes.

For example the Very Large Array has 27 telescopes giving 351 independent baselines at once.

For this reason, reaction wheels are often used to aim spacecraft with cameras or telescopes.

For small telescopes using spherical mirrors with focal ratios shorter than f / 10, light from a distant point source ( such as a star ) is not all focused at the same point.

For instance, some reported transient phenomena are for objects near the resolution of the employed telescopes.

For reflecting telescopes, which use a curved mirror in place of the objective lens, theory preceded practice.

For detailed information on specific designs of reflecting, refracting, and catadioptric telescopes: see the main articles on Reflecting telescopes, Refracting telescopes, and Catadioptrics.

For large ground-based telescopes, the resolution is limited by atmospheric seeing.

For conventional telescopes on Earth, the diffraction limit is not relevant for telescopes bigger than about 10 cm.

For telescopes with diameters smaller than r < sub > 0 </ sub >, the resolution of long-exposure images is determined primarily by diffraction and the size of the Airy pattern and thus is inversely proportional to the telescope diameter.

For telescopes with diameters larger than r < sub > 0 </ sub >, the image resolution is determined primarily by the atmosphere and is independent of telescope diameter, remaining constant at the value given by a telescope of diameter equal to r < sub > 0 </ sub >.

For telescopes with circular apertures, the size of the smallest feature in an image that is diffraction limited is the size of the Airy disc.

For much of the history of observational astronomy, almost all observation was performed in the visual spectrum with optical telescopes.

For visual observing, most notably on equatorial telescope mounts, tube orientation can put the eyepiece in a very poor viewing position, and larger telescopes require ladders or support structures to access it.

For research telescopes, counterbalancing very heavy instruments mounted at this focus has to be taken into consideration.