A cylindrical lens is a lens which focuses light into a line instead of a point, as a spherical lens would. The curved face or faces of a cylindrical lens are sections of a cylinder, and focus the image passing through it into a line parallel to the intersection of the surface of the lens and a plane tangent to it. The lens compresses the image in the direction perpendicular to this line, and leaves it unaltered in the direction parallel to it (in the tangent plane). In a light sheet microscope, a cylindrical lens is placed in front of the illumination objective to create the light sheet used for imaging.
A toric lens combines the effect of a cylindrical lens with that of an ordinary spherical lens.
The Ahırkap Feneri, a historical lighthouse still in use, is located at the southern Seraglio Point on the Rumelian coast of Bosporus' south entrance, in Ahırkapı neighborhood of Istanbul's Fatih district, Turkey. It is across from the Kadıköy İnciburnu Feneri, which is on the Anatolian coast of the strait at a distance of 1.5 nmi (2.8 km). A line connecting the two lighthouses marks the southern boundary of the Port of Istanbul.Astigmatism (optical systems)
An optical system with astigmatism is one where rays that propagate in two perpendicular planes have different foci. If an optical system with astigmatism is used to form an image of a cross, the vertical and horizontal lines will be in sharp focus at two different distances. The term comes from the Greek α- (a-) meaning "without" and στίγμα (stigma), "a mark, spot, puncture".Eyeglass prescription
An eyeglass prescription is an order written by an eyewear prescriber, such as an optometrist or ophthalmologist, that specifies the value of all parameters the prescriber has deemed necessary to construct and/or dispense corrective lenses appropriate for a patient. If an examination indicates that corrective lenses are appropriate, the prescriber generally provides the patient with an eyewear prescription at the conclusion of the exam.
The parameters specified on spectacle prescriptions vary, but typically include the patient's name, power of the lenses, any prism to be included, the pupillary distance, expiration date, and the prescriber's signature. The prescription is typically determined during a refraction, using a phoropter and asking the patient which of two lenses is better, or by automated refractor, or through the technique of retinoscopy. A dispensing optician will take a prescription written by an optometrist or ophthalmologist and order and/or assemble the frames and lenses to then be dispensed and sold to the patient.Fenerbahçe Lighthouse
The Fenerbahçe Lighthouse (Turkish: Fenerbahçe Feneri), a historical lighthouse still in use, is located on the northern coast of Sea of Marmara at Fenerbahçe neighborhood of Kadıköy district in Istanbul, Turkey.Fresnel lens
A Fresnel lens ( FREZ-nəl or fray-NEL) is a type of compact lens originally developed by French physicist Augustin-Jean Fresnel for lighthouses.The design allows the construction of lenses of large aperture and short focal length without the mass and volume of material that would be required by a lens of conventional design. A Fresnel lens can be made much thinner than a comparable conventional lens, in some cases taking the form of a flat sheet. A Fresnel lens can capture more oblique light from a light source, thus allowing the light from a lighthouse equipped with one to be visible over greater distances.GRENOUILLE
Grating-eliminated no-nonsense observation of ultrafast incident laser light e-fields (GRENOUILLE) is an ultrashort pulse measurement technique based on frequency-resolved optical gating (FROG). The acronym was chosen because of the technique's relationship to FROG; grenouille is French for frog.Laser beam profiler
A laser beam profiler captures, displays, and records the spatial intensity profile of a laser beam at a particular plane transverse to the beam propagation path. Since there are many types of lasers — ultraviolet, visible, infrared, continuous wave, pulsed, high-power, low-power — there is an assortment of instrumentation for measuring laser beam profiles. No single laser beam profiler can handle every power level, pulse duration, repetition rate, wavelength, and beam size.Lattice light-sheet microscopy
Lattice light-sheet microscopy is a modified version of light sheet fluorescence microscopy that increases image acquisition speed while decreasing damage to cells caused by phototoxicity. This is achieved by using a structured light sheet to excite fluorescence in successive planes of a specimen, generating a time series of 3D images which can provide information about dynamic biological processes.It was developed in the early 2010s by Eric Betzig. According to the Washington Post, Eric Betzig believes that this development will have a greater impact than the work that earned him the 2014 Nobel Prize in Chemistry for "the development of super-resolved fluorescence microscopy".Light sheet fluorescence microscopy
Light sheet fluorescence microscopy (LSFM) is a fluorescence microscopy technique with an intermediate-to-high optical resolution, but good optical sectioning capabilities and high speed. In contrast to epifluorescence microscopy only a thin slice (usually a few hundred nanometers to a few micrometers) of the sample is illuminated perpendicularly to the direction of observation. For illumination, a laser light-sheet is used, i.e. a laser beam which is focused only in one direction (e.g. using a cylindrical lens). A second method uses a circular beam scanned in one direction to create the lightsheet. As only the actually observed section is illuminated, this method reduces the photodamage and stress induced on a living sample. Also the good optical sectioning capability reduces the background signal and thus creates images with higher contrast, comparable to confocal microscopy. Because LSFM scans samples by using a plane of light instead of a point (as in confocal microscopy), it can acquire images at speeds 100 to 1000 times faster than those offered by point-scanning methods.
This method is used in cell biology and for microscopy of intact, often chemically cleared, organs, embryos, and organisms.Starting in 1994, LSFM was developed as orthogonal plane fluorescence optical sectioning microscopy or tomography (OPFOS) mainly for large samples and later as the selective/single plane illumination microscopy (SPIM) also with sub-cellular resolution. This introduced an illumination scheme into fluorescence microscopy, which has already been used successfully for dark field microscopy under the name ultramicroscopy.Line laser
A line laser is a laser modified to project a line rather than a point (e.g. laser pointer). This may be achieved by passing the beam through a cylindrical lens or a Powell lens.
Using multiple lasers, it is possible to project multiple lines for use with image processing.
Depending on the application, line lasers can generate lines, crosses or other patterns. Civil engineering and interior design projects can use line lasers to measure the levelling of a small building site.List of instruments used in ophthalmology
This is a list of instruments used in ophthalmology.Particle image velocimetry
Particle image velocimetry (PIV) is an optical method of flow visualization used in education and research. It is used to obtain instantaneous velocity measurements and related properties in fluids. The fluid is seeded with tracer particles which, for sufficiently small particles, are assumed to faithfully follow the flow dynamics (the degree to which the particles faithfully follow the flow is represented by the Stokes number). The fluid with entrained particles is illuminated so that particles are visible. The motion of the seeding particles is used to calculate speed and direction (the velocity field) of the flow being studied.
Other techniques used to measure flows are laser Doppler velocimetry and hot-wire anemometry. The main difference between PIV and those techniques is that PIV produces two-dimensional or even three-dimensional vector fields, while the other techniques measure the velocity at a point. During PIV, the particle concentration is such that it is possible to identify individual particles in an image, but not with certainty to track it between images. When the particle concentration is so low that it is possible to follow an individual particle it is called Particle tracking velocimetry, while Laser speckle velocimetry is used for cases where the particle concentration is so high that it is difficult to observe individual particles in an image.
Typical PIV apparatus consists of a camera (normally a digital camera with a CCD chip in modern systems), a strobe or laser with an optical arrangement to limit the physical region illuminated (normally a cylindrical lens to convert a light beam to a line), a synchronizer to act as an external trigger for control of the camera and laser, the seeding particles and the fluid under investigation. A fiber optic cable or liquid light guide may connect the laser to the lens setup. PIV software is used to post-process the optical images.Photographophone
A photographophone is a device that was first developed by Ernst Ruhmer of Berlin, Germany in 1900. The Photographophone could record and reproduce speech and music through a celluloid film. The process started by speaking into a microphone. The electrical signal from the microphone through a transformer supplied electric current from a battery pack that caused a corresponding variation in the light of an arc (later used an incandescent lamp). The light from the arc lamp passes through the cylindrical lens slot which created sharp white lines on the moving sensitive film. This film, after being taken out of the box and developed, shows a series of perpendicular striations parallel to one another, which are really a photographic record of the sound waves originally entering the telephone transmitter.
To reproduce the sound an projector directs light through the film traveling with the velocity equal to that with which the record is made. Behind the film a sensitive selenium cell is mounted receiving the variations in light producing a variation in its resistance and a corresponding effect in the telephone receivers connected.
"It is truly a wonderful process: sound becomes electricity, becomes light, causes chemical action, becomes light and electricity again, and finally sound."Single-particle tracking
Single-particle tracking (SPT) is the observation of the motion of individual particles within a medium. The coordinates time series, which can be either in two dimensions (x, y) or in three dimensions (x, y, z), is referred to as a trajectory. The trajectory is typically analyzed using statistical methods to extract information about the underlying dynamics of the particle. These dynamics can reveal information about the type of transport being observed (e.g., thermal or active), the medium where the particle is moving, and interactions with other particles. In the case of random motion, trajectory analysis can be used to measure the diffusion coefficient.Stanhope (optical bijou)
Stanhopes or Stanho-scopes are optical devices that enable the viewing of microphotographs without using a microscope. They were invented by René Dagron in 1857. Dagron bypassed the need for an expensive microscope to view the microscopic photographs by attaching the microphotograph at the end of a modified Stanhope lens. He called the devices bijoux photo-microscopiques or microscopic photo-jewelry. In 1862, Dagron displayed the devices at the Exhibition in London, where he got an "Honourable Mention" and presented them to Queen Victoria. In 1864 Dagron became famous when he produced a stanhope optical viewer which enabled the viewing of a microphotograph 1 square millimetre (0.0016 sq in), (equivalent in size to the head of a pin), that included the portraits of 450 people.Stigmator
For the photographic lens astigmatism correction lens see Anastigmat.A stigmator is a component of electron microscopes that reduces astigmatism of the beam by imposing a weak electric or magnetic quadrupole field on the electron beam.Sundial
A sundial is a device that tells the time of day when there is sunlight by the apparent position of the Sun in the sky. In the narrowest sense of the word, it consists of a flat plate (the dial) and a gnomon, which casts a shadow onto the dial. As the Sun appears to move across the sky, the shadow aligns with different hour-lines, which are marked on the dial to indicate the time of day. The style is the time-telling edge of the gnomon, though a single point or nodus may be used. The gnomon casts a broad shadow; the shadow of the style shows the time. The gnomon may be a rod, wire, or elaborately decorated metal casting. The style must be parallel to the axis of the Earth's rotation for the sundial to be accurate throughout the year. The style's angle from horizontal is equal to the sundial's geographical latitude.
In a broader sense, a sundial is any device that uses the Sun's altitude or azimuth (or both) to show the time. In addition to their time-telling function, sundials are valued as decorative objects, literary metaphors, and objects of mathematical study.
It is common for inexpensive, mass-produced decorative sundials to have incorrectly aligned gnomons and hour-lines, which cannot be adjusted to tell correct time.Toric lens
A toric lens is a lens with different optical power and focal length in two orientations perpendicular to each other. One of the lens surfaces is shaped like a "cap" from a torus (see figure at right), and the other one is usually spherical. Such a lens behaves like a combination of a spherical lens and a cylindrical lens. Toric lenses are used primarily in eyeglasses, contact lenses and intraocular lenses to correct astigmatism.Yeşilköy Feneri
Yeşilköy Feneri is a historical lighthouse still in use located on the northern coast of Sea of Marmara at Yeşilyurt neighborhood (once part of Yeşilköy) in Istanbul's Bakırköy district, Turkey.