Photonics Dictionary

The organ of vision or light sensitivity.

The area in a 2-D or 3-D microdisplay viewer within which the eye can move and still see the entire image.

A shield of rubber, plastic or metal used to protect the eyes of the observer from stray light and wind, and to maintain the proper eye distance.

The lens of an eyepiece nearest the observer's eye.

A pattern on an oscilloscope display that consists of a string of shapes that resemble eyes. Because the pattern becomes more closed with increasing distortion and interference, an open eye diagram...

Also termed eye distance. The distance between the vertex of the last optical surface of a visual optical system and the system's exit pupil.

Instruments used by ophthalmologists and optometrists to study the eye. There are, for instance, the ophthalmoscope to observe and photograph the retina; the retinoscope and optometer to determine...

An optical device used to monitor movement of the human eye.

Wavelengths between 400 and 1400 nm (VIS to NIR) are focused onto the retina by the cornea. Because the retina is sensitive to light, these wavelengths can be damaging even at low energies. It is the...

Also known as ocular. The lens system used between the final real image in a visual optical system and eye. It acts as an image magnifier. Many types of eyepieces are known; e.g., the Huygens used in...

In a visual optical system, the axial distance from the last mechanical surface of the eyepiece to the exit pupil.

A microscope eyepiece designed for use with apochromatic objectives. Since apochromatic objectives are undercorrected for lateral color, these eyepieces are overcorrected for that aberration.

An eyepiece used in a polariscope or polarizing microscope to give a comparison view of the same object under illumination by the two complementary rays of polarized light.

An eyepiece combined with an erecting prism or lens system.

A telescopic eyepiece comprising five or six simple lenses in the form of three doublets or two doublets and a singlet.

A measuring eyepiece with a screw-micrometer-driven crosshair used to measure the size of the image.

A type of wide-angle lens that has an angular field above 140° and that exhibits barrel distortion. The most commonly used fish-eye lenses have a field of about 180°, though they are...

An eyepiece having a rotating index or cross wire linked to an external 360° scale to allow measuring of angles in an image.

An ocular having two planoconvex lenses that are formed from similar glass and that are separated by a space equal to half the sum of their focal lengths. This eyepiece is free of lateral chromatic...

An eyepiece similar to the Huygenian eyepiece, but having an eye lens that is a cemented doublet and that provides more lateral color correction.

An eyepiece having a special prism arrangement linked to a micrometer screw to allow reading of the angular relations between the two prism segments to be varied. When the prism faces are parallel,...

An eyepiece consisting of a planoconvex field lens and a cemented doublet as the eye lens.

Usually consists of a set of filters that attenuate specific wavelengths but transmit as much visible radiation as possible.

A wireless stereo imaging device used in conjunction with a monitor to produce a virtual interactive environment. Liquid crystal shutters in the eyewear are synchronized with the monitor at 120...

Also known as an eyepiece micrometer. A microscope eyepiece that has a finely divided scale ruled or photographed on a section of transparent glass, and located in the focal plane. The dimensions of...

An eyepiece located at the near end of the microscope tube. It often is a simple Huygens eyepiece, but compensating and flat-field projection eyepieces are quite efficient. Negative eyepieces are...

The closest distance to which the eye can focus on an object, normally taken to be 250 mm. The near point varies with age.

A telescopic eyepiece that produces a field of view between 40° and 50°. The eyepiece consists of a single element eyelens that is normally plano convex, and a cemented triplet that is...

One eyepiece of a set having equal distances from their mounting interface to their image plane, permitting freedom to interchange eyepieces without the need to refocus.

A well-corrected flat-field eyepiece with good eye relief. Similar to a Huygenian.

A type of eyepiece, or the modification of an eyepiece, in which a small hole, without a lens, functions as the eye lens; used in the adjustment and alignment of microscopes.

A Huygenian eyepiece containing a pointer at its focal plane that is used -- when viewing an object through the eyepiece -- for specific designation.

An eyepiece consisting of two planoconvex lenses of the same focal length, with facing convex surfaces.

An eyepiece or magnifier capable of covering a field of view that is greater than 50°.

Equipment for testing an observer's color vision. Some tests require the identification or ordering of colored samples. The commercially available examples include: the Ishihara plates, on which...

The alteration and reduction of color with the addition of white light. The perceived color shift that occurs as the monochromatic-white combination meets the eye and is interpreted by the brain. The...

The value of the distance of distinct vision, minimum focusing distance or near point, divided by the focal length of the lens. Magnification is produced when the optic is placed at its focal...

An apparatus used to determine the degree of adaptation of the eye under different conditions.