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Glossary

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ibn-Sahl law: see Snell's law
illuminated field: The area of the sample that is illuminated by the microscope light source. It is adjusted by the illuminated field stop.; See also: illuminated field stop, field stop, illumination, object plane
illuminated field diaphragm: see illuminated field stop
illuminated field stop: The field stop that controls the total area of sample illumination. It is located in a conjugate field plane in the illumination optics.; Synonyms: illuminated field diaphragm; See also: Köhler illumination, conjugate planes, optical train, field stop, stop
illuminating aperture: see condenser aperture stop
illuminating aperture diaphragm: see illuminating aperture stop
illuminating aperture stop: The aperture stop that controls the angle of sample illumination, and thus resolution and depth of field. It is located in a conjugate aperture plane in the illumination optics.; Synonyms: illuminating aperture diaphragm; See also: Köhler illumination, conjugate planes, optical train, aperture stop, stop
illumination: The application of light to an object to facilitate observation.; See also: Köhler illumination, conjugate planes, optical train
illumination optical path: see illumination path
illumination path: The optical path through which illumination light passes through. It typically consists of a light source, collector lens, field stop, aperture stop, and condenser lens.; Synonyms: illumination optical path; See also: Köhler illumination, conjugate planes, optical train, illumination, field stop, aperture stop, condenser, collector lens
illuminator: A device providing illumination for microscopy, it principally includes a light source such as a light emitting diode or halogen lamp.; See also: light source, optical train, light emitting diode, halogen lamp
image: The reconstructed spatial view of a object/scene created by refocusing light modulated by said object/scene onto a detector using an optical system.; See also: image plane, detector
image based autofocus: An autofocusing strategy based on characteristics of the observed image, such as contrast or brightness. Newer strategies incorporate trained AI networks to identify features such as cells.; See also: reflected-light based autofocus, perfect focus system, focus
image field: see image plane
image intensifier: A device that receives incoming photons which are converted to an electrical signal, amplified, and projected out as photons again. Useful for low-light applications.; Synonyms: image intensifier tube
image intensifier tube: see image intensifier
image plane: The set of conjugate field planes where an image of the object is formed. The eyepiece field stop, object plane, and retina or camera chip are typical image plane locations.; Synonyms: image field; See also: conjugate planes, aperture plane, field plane, image
image restoration: see deconvolution
image scanning microscopy (ISM): Usually implemented in a point-scanning confocal or multiphoton system, ISM makes it possible to realize the full theoretical ~2X resolution improvement of a confocal system with usable signal levels. ISM relies on a small detector array, with each pixel acts as a very small pinhole, providing its own image of the object. Shifting and summing of these sub-images provides the super-resolution image.; See also: confocal, confocal microscopy, multiphoton microscopy, structured illumination microscopy, super-resolution, single-photon avalanche diode array
image space: The set of real space spatial dimensions that an object and its image exist in. The Fourier transform is used to transform image space information into the spatial frequency domain (Fourier space). The term "image space" may also be used in reference to depth of focus.; Synonyms: real space; See also: frequency space, Fourier optics, Fourier transform, depth of focus
image stack: A set of 2D images organized by an additional dimension, such as depth or time. Multiple dimensions can be nested, such as multichannel fluorescence timelapse experiments.; Synonyms: multidimensional image dataset; See also: Z stack
image stitching: A post-processing analysis step, where multiple images captured in adjacent regions of a specimen are aligned and computationally merged to form one, large image.; Synonyms: stitching, image tiling, tiling; See also: shading correction
image tiling: see image stitching
image-forming planes: see field plane
imaging aperture: The aperture of the imaging system, it is typically defined by the aperture of the objective lens and determines the numerical aperture (NA).; See also: aperture, numerical aperture
imaging modality: see contrasting technique
immersion: The use of a (non-air) fluid between an optical component, usually the objective and/or condenser lens, and the sample in order to better match the refractive index of the sample medium or mounting medium.; See also: refractive index, immersion medium, immersion lens, immersion objective, homogenous immersion, mounting medium
immersion lens: see homogenous immersion
immersion medium: A medium such as oil that is applied between the sample and a specified immersion objective lens to maintain a consistent refractive index between the two.; See also: immersion, immersion objective, refractive index
immersion objective: An objective lens designed for use with a given immersion medium between it and the sample. This allows for the refractive index to be closely matched with that of the sample medium or mounting medium, minimizing aberrations and maximizing numerical aperture.; Synonyms: immersion lens; See also: immersion, immersion medium, refractive index
in vitro fertilization (IVF): A fertility treatment technique in which the male sperm and female egg are combined under a microscope in vitro.; See also: assisted reproductive technology, intracytoplasmic morphologically selected sperm injection, intracytoplasmic sperm injection
incident optical unit (IOU): A device that couples incident light, such as infrared (IR) laser light, from the light source to the microscope system. It is capable of minor adjustments such as alignment to optimize illumination.; See also: multiphoton microscopy, multiphoton excitation
incoherent imaging system: An imaging system where the illumination and detection light are highly incoherent (e.g., fluorescence) and thus mostly free from interference artifacts such as speckle. The impulse response of such a system is the intensity point-spread function.; See also: coherent imaging system, spatially coherent illumination, temporally coherent illumination, intensity point-spread function
index ellipsoid: A three-dimensional representation of the refractive indices of an isotropic, uniaxial, or biaxial material, where the length of each axis is proportional to the refractive index of that material along that axis.; Synonyms: optical indicatrix; See also: birefringence, polarized light, polarized light microscopy
inelastic scattering: Scattering where some amount of energy is transferred to (or received from) from the scattering material.; See also: elastic scattering, Raman scattering, Brillouin scattering, fluorescence
infinity corrected objective: see normal tube lens
infinity correction: see infinity optical system
infinity objective: see infinity-corrected objective
infinity optical system: A microscope system where the objective lens does not form an intermediate image, but rather projects collected light as a collimated beam such that the image distance would be at infinity. A tube lens focuses the collimated beam to form an image. This design is popular because components such as filters may be inserted into the "infinity space".; Synonyms: infinity correction; See also: infinity-corrected objective, finite intermediate image distance objective, fixed tube length system
infinity-corrected objective: An objective lens that collects light from the object at the front focal plane of the objective and projects an image at infinity. This requires a subsequent tube lens to focus the collimated light into an image.; Synonyms: infinity objective; See also: infinity optical system
infrared: see infrared radiation
infrared absorption microscopy: see infrared microscopy
infrared differential interference contrast (IR-DIC): Differential interference contrast (DIC) microscopy utilizing near-infrared wavelengths (~850 - 950 nm) to achieve better sample penetration due to the reduced scattering of longer wavelengths.; Synonyms: near-infrared DIC, NIR-DIC; See also: differential interference contrast, near-infrared radiation
infrared filter: see heat filter
infrared light: see infrared radiation
infrared microscopy: Infrared microscopes use reflection-based (catoptric) optical components compatible with infrared radiation, such as Cassegrain objective lenses, and can be transmission or reflection-based. A Fourier transform infrared (FT-IR) spectrometer is commonly used to measure absorption across a wide spectral range.; Synonyms: infrared microspectroscopy, infrared absorption microscopy; See also: radiation, electromagnetic spectrum, infrared radiation
infrared microspectroscopy: see infrared microscopy
infrared radiation: Infrared radiation covers from ~750 nm - 1000 µm on the electromagnetic spectrum, depending on the classification standard. It has been further sub-divided into near-infrared (750 - 1400 nm), short-wave (1.4 - 3.0 µm), mid-wave (3.0 - 8.0 µm), long-wave (8.0 - 15.0 µm), and far-infrared (15 - 1000 µm).; Synonyms: infrared light, infrared; See also: infrared microscopy, infrared differential interference contrast, near-infrared radiation
intensity: Intensity can refer to a number of different physical quantities, including radiant intensity, which is the radiant flux per solid angle and is a directional parameter (watts/steradian). It can be described by the square of the incoming electromagnetic field amplitude at a given area. Signal strength from a detector measures intensity.; See also: intensity point-spread function
intensity point-spread function (PSF): The intensity point spread function is the amplitude point spread function squared. The amplitude PSF describes the spatial distribution of the electromagnetic field of an image of a point source, while the intensity PSF describes the measurable intensity of this field.; See also: point-spread function, amplitude point-spread function
interfacing dimensions: Standardized dimensions described by the International Organization for Standardization (ISO) governing lens and lens-fixing component (such as threading) parameters.
interference: A general property of waves in which coincident waves combine to form a resultant pattern depending on the sign (positive or negative) and amplitude of the component waves. Can be constructive or destructive. Diffraction patterns are caused by interference.; See also: diffraction, polarized light, polarized light microscopy, interference colors, interference contrast, interferometry, interference filter
interference colors: Colors produced by interference of white light waves with the same polarization and a well-defined phase relationship. Interference colors are commonly generated when imaging a birefringent sample using polarized light microscopy - a Michel-Lévy chart can be used to identify materials based on color and thickness.; Synonyms: Newton's colors; See also: birefringence, polarized light microscopy, interference, polarization
interference contrast: The generation of contrast based on interference between two component light waves. This is the underlying principle of differential interference contrast (DIC) microscopy, where the illumination is laterally sheared into a pair of parallel beams which experience different optical path lengths - this becomes the source of contrast once the beams are recombined and interfere.; See also: differential interference contrast, interference, interference colors, interferometry
interference filter: A filter composed of multiple thin layers of material with varied refractive indices. Based on layer thickness and composition, certain wavelengths of light can be amplified or reduced based on intra-filter reflections. These filters can be long-, short-, or band-pass and are useful for applications such as fluorescence microscopy.; Synonyms: dichroic filter, thin-film filter; See also: filter, fluorescence microscopy, excitation filter, emission filter, bandpass filter, longpass filter, shortpass filter
interferometry: Techniques based on interference of light from a single source that has been split along multiple lightpaths. For example, incident light is split into a control path to a mirror and a path to the sample. The reflected light from both paths is combined and the resulting interference pattern can be used to measure differences in optical path length.; See also: interference, coherent imaging system
intermediate image: An image plane occurring after the sample and prior to the final image at the retina or detector, often located at the eyepiece field stop.; Synonyms: intermediate image plane; See also: conjugate planes, field plane, image plane, primary image
intermediate image plane: see relay lens
intermediate lens: Lens located between the objective lens and the primary image that can be used to adjust magnification.; See also: optical train
intermediate tube: An optional tube used in a microscope containing some type of optomechanical components for insertion into the light path.; See also: tube
internal-diaphragm eyepiece: see Huygens eyepiece
interpupillary distance: The distance between a person's pupils (in millimeters); See also: eyepiece, observation tube
intracytoplasmic morphologically selected sperm injection (IMSI): A type of intracytoplasmic sperm injection (ICSI) technique in which individual sperm cells are examined under the microscope and specifically selected for fertilization.; See also: in vitro fertilization, assisted reproductive technology
intracytoplasmic sperm injection (ICSI): The injection of a sperm cell into the cytoplasm of an egg cell to induce fertilization.; See also: in vitro fertilization, assisted reproductive technology, intracytoplasmic morphologically selected sperm injection
inverted microscope: A microscope in which the objective lens is located below the sample. Useful for live cell applications where cells are adhered to the bottom coverslip of a dish filled with media.; See also: upright microscope, microscope
IR filter: see heat filter
iris diaphragm: An optical component consisting of overlapping leaves that can be opened or closed to form an approximately circular aperture of a specific diameter.; See also: aperture stop, field stop, stop