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Pancharatnam-Berry geometric phase: see geometric phase
pancratic condenser: A condenser with a variable zoom lens which allows the field size at the illumination plane to be varied.; See also: condenser
parallel polarizers: A set of linear polarizers aligned parallel to one another. This maximizes the transmission of light in a polarized light microscopy system.; See also: polarized light, polarized light microscopy, polarizer, analyzer
parallel ray: In ray tracing, the ray traveling from the object parallel to the optical axis and refracted by the lens to pass through its back focal plane.; See also: ray, ray tracing, characteristic rays, focal ray, geometric optics
paraxial approximation: In ray tracing, restricting consideration of rays to those that converge/diverge at a small angle relative to the optical axis. This allows for trigonometric functions using these angles to be approximated as linear functions, simplifying calculations for parameters such as magnification and focal length.; Synonyms: small-angle approximation; See also: ray, ray tracing, geometric optics, Gaussian optics
parfocality: The property of any lens in a set (e.g., objective lens, eyepiece) such that if it is focused on the object and another lens in the set is moved into its position, the object will remain largely in-focus. However, it is normal for some small focus adjustments to be necessary.; Synonyms: parfocalizing distance of the eyepiece, parfocalizing distance of the objective
parfocalizing distance of the eyepiece: see parfocality
parfocalizing distance of the objective: see parfocality
patch-clamp recording: A technique in which a micropipette is used to probe electrical currents passing across cellular membranes,; See also: electrophysiology
perfect focus system (PFS): A system developed by Nikon which utilizes near-infrared light to track and maintain a steady position between the objective lens and sample coverslip.; See also: reflected-light based autofocus
perfect lens: A hypothetical lens exhibiting zero aberrations and able to focus light to a single point. It is a useful concept for ray tracing.; See also: ray tracing, geometric optics
Petzval curvature: see field curvature
Petzval field curvature: see field curvature
phase: A wave property that defines its relative cyclical position in space or time. A single cycle can be expressed as 2pi radians, 360 degrees, or a full wavelength (lambda). Waves that are "in phase" are at the same cyclical position at a given point in space/time.; See also: phase difference, phase object, phase contrast microscopy
phase annulus: Used in phase contrast microscopy, a phase annulus is a ring-shaped illumination mask located in the front focal plane of the condenser and conjugate with the phase plate in the detection optics. Phase contrast condensers typically have multiple phase annulus modules.; See also: phase plate, phase contrast microscopy, positive phase contrast microscopy, negative phase contrast microscopy, phase contrast condenser
phase contrast: see label-free
phase contrast condenser: An optical assembly containing the condenser lens system and phase annulus modules of different sizes that are optimized for different objective lens numerical aperture (NA) ranges. Nikon designates these different sizes as PhL, Ph1, Ph2, Ph3, and Ph4 in order of optimization for increasing NA.; See also: phase, phase difference, phase object, phase plate, phase annulus, phase contrast microscopy
phase contrast microscopy: Briefly, a phase annulus is used as a circular illumination mask. A phase plate with matching circular modulator is in a conjugate aperture plane in the detection optics (typically the objective back focal plane). It attenuates and imparts a small phase shift to the un-diffracted 0th order light. Diffracted light (mostly) does not traverse the phase plate and is unattenuated – its interference with 0th order light in the image generates contrast.; Synonyms: phase contrast; See also: phase, phase difference, phase object, phase plate, phase annulus, positive phase contrast microscopy, negative phase contrast microscopy, phase contrast condenser
phase difference: The difference in phase between two waves of light traveling in the same direction at a given location and time. Also assuming monochromatic light and significant overlap, phase differences between waves equal to multiples of one wavelength result in perfectly constructive interference, while multiples of one half wavelength result in perfectly destructive interference.; See also: phase, interference, monochromaticity
phase object: An object that modulates the phase of light it diffracts relative to the un-diffracted 0th order light. Note that the overall intensity of the light is generally unaffected.; See also: phase, phase difference
phase plate: Used in phase contrast microscopy, a phase plate is (usually) placed in the objective lens back focal plane and features a circular modulator conjugate to the circular illumination mask of the phase annulus. It both attenuates light passing through it and advances or retards its phase by a quarter wavelength.; See also: phase annulus, phase contrast microscopy, positive phase contrast microscopy, negative phase contrast microscopy, phase contrast condenser
phase telescope: A magnifying lens assembly that fits into an eyepiece position in the observation tube and allows for visual observation of the aperture set of conjugate planes, including the conoscopic figure.; Synonyms: centering telescope; See also: conjugate planes, Bertrand lens, conoscopy, conoscopic figure
phase transfer function (PTF): The complex argument of the optical transfer function (OTF), it captures the effects of phase shifts (often due to optical aberrations) on the OTF.; See also: modulation transfer function, optical transfer function, contrast transfer function
phenotypic screening: An approach to discover substances (e.g., small molecules) that provide a desirable change in phenotype, useful in disciplines such as drug discovery. High throughput imaging and high content imaging are popular methods for phenotypic screening.; See also: high throughput imaging, high content imaging
photoactivated localization microscopy (PALM): A super-resolution microscopy technique, which employs optical highlighter fluorescent proteins (FPs) to temporally separate the emission profiles of individual FPs. As with other single molecule localization microscopies, PALM provides resolution enhancement by localizing the centroid position of each emission profile.; See also: single molecule localization microscopy, DNA-PAINT, stochastic optical reconstruction microscopy, super-resolution
photobleaching: The permanent alteration of a fluorophore, where it is unable to fluoresce. This is typically a result of prolonged excitation making the fluorophore prone to chemical alteration (e.g., oxidation by components in the imaging medium).; See also: phototoxicity, fluorophore, fluorescence, fluorescence recovery after photobleaching
photoconversion: A change in a fluorophore's emission wavelength, typically due to a conformational change in a fluorescent protein when irradiated with high-energy (i.e. blue-shifted) light.
photodiode: A semiconductor diode which converts incident light to an electric current.
photographic projection lens: A lens used to project an image onto photographic film.
photomacrography: A photography technique which focuses on close up, highly detailed photographs of small subjects. Typical subjects include insects and plant life.
photomicrograph: see photomicrography
photomicrography: A photograph of a subject under a microscope.; Synonyms: photomicrograph
photomultiplier tube (PMT): A type of vacuum tube that converts incident light into electrons (photoelectrons) and amplifies the signal into a detectable charge. PMTs are commonly used as single-pixel detectors in confocal microscopy. Sensitivity at different wavelengths varies with the photocathode material.; See also: GaAsP photomultiplier tube, multi-alkali photomultiplier tube, detector
photostimulation: The use of light to somehow stimulate a change in a biological system or any probes or actuators that were introduced into it. Photostimulation is often performed using targeted laser illumination with a device such as an XY-scanning galvanometer system.; See also: confocal microscopy, point-scanning confocal microscopy
phototoxicity: This is a general term for any deleterious effects of light exposure in a biological system. It is often used in the context of live-cell fluorescence imaging due to the intense illumination required by such techniques. Phototoxicity is especially pronounced with shorter wavelengths.; See also: photobleaching, fluorophore, fluorescence, fluorescence microscopy
physical optics: see wave optics
pincushion distortion: A geometric aberration where magnification increases as you move from the center of the image to the outside.; See also: aberration, barrel distortion
pinhole: In confocal microscopy, one or more pinhole apertures are used in a field plane in the emission light path, helping to reject out-of-focus light. This improves optical sectioning, resulting in a sharper image with less blur.; See also: confocal, confocal microscopy, optical section
pinhole crosstalk: A loss of confocality in a spinning disk confocal microscope, it is the result of light emitted from a spot on the sample that is conjugate with one pinhole also passing through adjacent pinholes. This leads to reduced optical sectioning and image quality, but can be mitigated by using a greater pinhole spacing.; See also: Nipkow disk, spinning disk confocal microscopy
pixel: The smallest quantifiable portion of a digital image, it is also used in reference to the smallest detector element in an array sensor, as used in digital cameras.; See also: pixel size, hot pixel, dead pixel, voxel, camera
pixel binning: see binning
pixel size: The physical size of individual pixels on an image sensor.; See also: pixel, Nyquist sampling, charge coupled device, electron multiplying charge coupled device, scientific complementary metal-oxide-semiconductor detector
plan achromat objective: An objective lens that is corrected for axial chromatic aberration at two wavelengths (in the red and blue) and also corrected for field curvature.; See also: objective lens, chromatic aberration, axial chromatic aberration, curvature of field, plan objective, achromat objective
plan objective: An objective lens that has been corrected for flatness of field, given the natural curvature of the image plane by a simple lens.; Synonyms: flat-field objective; See also: objective lens
plane wave: An electromagnetic wave that is both invariant over a plane normal to the direction of propagation and transverse.; See also: wave, wavefront, spherical wave
plane-polarized light: see linearly-polarized light
Poincaré sphere: An approach to visualize the polarization state of an electromagnetic wave, where the three axes correspond to different Stokes parameters and define a spherical coordinate system.; See also: polarization, polarized light microscopy, geometric phase
point detection: The detection of signal from a diffraction-limited spot in the sample.; See also: point detector, point-scanning confocal microscopy
point detector: A device for detecting light that uses a single light-sensitive detecting element. An example would be a photomultiplier tube, as commonly used in confocal microscopy.; Synonyms: single element detector; See also: photomultiplier tube, confocal microscopy
point scanning confocal microscopy: see line-scanning confocal microscopy
point source: A point of light emitted from a singular location.; See also: single molecule localization microscopy
point-scanning: An imaging technique where a light source is raster scanned across a sample and synchronized with a point detector to build an image. This is the basic mechanism used in point-scanning confocal microscopy.; Synonyms: spot-scanning; See also: scanning, point-scanning confocal microscopy, point detector
point-scanning confocal microscopy: A microscopy technique which captures images by raster scanning the object with a focused point of laser light. Light emitted by the object passes through a pinhole aperture in a conjugate field plane, helping to block out-of-focus light, and imaged using a point detector, such as a photomultiplier tube.; See also: confocal microscopy, confocal, point detector, point detection, image scanning microscopy
point-spread function (PSF): A quantitative representation of the image of a point source formed by a given imaging system. It is the impulse response of the microscope system. It is further defined as either the amplitude or intensity PSF. The optical transfer function (OTF) of a system is the Fourier transform of the PSF.; See also: amplitude point-spread function, intensity point-spread function, optical transfer function
point-spread function engineering: Purposeful alteration of the properties of the point-spread function (PSF) for a specific purpose, generally using a phase mask or some type of spatial light modulator in an aperture plane. For example, a tetrapod PSF makes is possible to encode information on the axial (Z) position of a point source in a 2D image.; See also: point-spread function, spatial light modulator
pointer eyepiece: A microscope eyepiece fitted with a pointed reticle, useful for keeping track of the relative movement of an object under observation.; See also: eyepiece
pointillist microscopy: see single molecule localization microscopy
polarization: see Poincaré sphere
polarization extinction ratio: see extinction ratio
polarization microscope: see polarized light microscopy
polarization microscopy: see polarized light microscopy
polarized light: A wavefront of light with common polarization state. Light can be linearly, elliptically, or circularly polarized. The polarization state is additionally defined by parameters such as handedness, ellipticity, etc.; See also: elliptically-polarized light, circularly-polarized light, linearly-polarized light
polarized light microscope: see first order yellow
polarized light microscopy (PLM): Briefly, the illumination is linearly polarized using a polarizer (east-west). A second polarizer (analyzer) is positioned in a crossed position in the detection optics (north-west), blocking all east-west linearly polarized light. Only light that has had its polarization state altered by interaction with a birefringent sample has the potential to pass the analyzer.; Synonyms: polarized light microscope, polarization microscopy, polarization microscope; See also: polarized light, polarizer, analyzer, birefringence
polarized light ordinary ray: see Nomarski prism
polarizer: An optical filter which only allows linearly polarized light of a narrow range of polarization angles to pass through.; Synonyms: linear polarizer, polarizing filter; See also: polarization, polarized light microscopy, analyzer
polarizing beamsplitter: A beamsplitter that splits an incident beam based on polarization state, transmitting p-polarized light and reflecting s-polarized.; See also: beamsplitter, polarized light
polarizing filter: see filter
polarizing interference: Refers to the type of interference that occurs in a polarized light microscopy system. Linearly polarized light is divided into ordinary and extraordinary rays by a birefringent specimen - the components of those two rays that pass through the analyzer are polarized in the same plane and interfere.; See also: polarized light, polarized light microscopy, birefringence, ordinary ray, extraordinary ray, polarizer, analyzer
polarizing prism: A type of prism composed of two birefringent materials which divides an incident beam of light into its ordinary and extraordinary components. A Nicol prism is a type of polarizing prism.; See also: polarizer, ordinary ray, extraordinary ray, birefringence, polarized light
polychromatic radiation: Electromagnetic radiation composed of more than one wavelength.; See also: radiation, electromagnetic spectrum
positive phase contrast: see positive phase contrast microscopy
positive phase contrast microscopy: Phase contrast microscopy where the phase plate advances the un-diffracted light relative to the diffracted light by a quarter wavelength (λ/4). Since diffracted light is already retarded by ~λ/4 through interaction with the object, the result is a half-wave phase difference and destructive interference.; Synonyms: positive phase contrast; See also: phase, phase object, phase plate, phase difference, phase contrast microscopy, interference, negative phase contrast microscopy
PreciPoint series: Developed and produced by PreciPoint GmbH, this inverted microscope lineup is known for ease of use, compact form factor and modern acquisition software. PreciPoint microscopes come in a variety of models with varying illumination and immersion options.; See also: whole slide imaging
primary diffraction pattern: In the Abbe theory of image formation, the primary diffraction pattern is formed in the back focal plane of the objective, and goes on to form the image of the specimen.; See also: diffraction, diffraction pattern, back focal plane, aperture plane
primary fluorescence: see autofluorescence
primary image: The first image formed by an objective lens in a fixed tube length system or objective lens together with tube lens in an infinity corrected system. This image may or may not also be an intermediate image or the final image.; See also: primary image plane, intermediate image, final image, image
primary image plane: The location where the primary image is formed in a microscope.; See also: primary image, intermediate image, final image
principal planes: Hypothetical planes formed by a lens perpendicular to the optical axis - useful for simplifying ray tracing. The principal object plane is where incident rays passing through the front focal point appear to be refracted parallel to the optical axis. The principal image plane is where incident light parallel to the optical axis appears to be refracted before converging through the back focal point.; See also: ray tracing, geometric optics, principal points
principal points: One of the sets of cardinal points of a lens, which is the intersection of the principal planes and the optical axis.; See also: ray tracing, geometric optics, principal planes
principal ray: In ray tracing, a ray traveling from an off-axis point in the field of view and directly through both principal points, appearing to pass straight through the center of a lens undeviated.; See also: ray, ray tracing, characteristic rays, chief ray, geometric optics, marginal ray, principal planes
prism: An optical element typically composed of glass and primarily designed to somehow alter incident light. For example, dispersing prisms are used for spectral dispersion of white light into its constituent wavelengths.; See also: optical train, dispersion, refractive index
projection factor: Any additional magnification introduced when projecting a real image of the object onto a detector.; See also: magnification, lateral magnification, projection lens
projection lens: A lens which can be used to form a real image of the primary image of the object at a defined location, such as on the detector, a plane for drawing, etc.; See also: projection factor
pupil: This term may refer to either an aperture plane or the entrance and exit pupils of the optical system.; See also: aperture plane, microscope entrance pupil, microscope exit pupil, pupil function
pupil function: The Fourier transform of the amplitude point-spread function (PSF). The amplitude transfer function and the pupil function are essentially the same, but by convention the pupil function is dimensionless and normalized to a value between 0 and 1. The optical transfer function is the autocorrelation of the pupil function.; Synonyms: generalized pupil function, complex pupil function; See also: amplitude transfer function, amplitude point-spread function, intensity point-spread function, optical transfer function, Fourier transform