Optics, Lenses & Filters
60 terms · page 1 of 3
Acutance
The abruptness of the transition at an edge, which the eye reads as sharpness independently of true resolution.
Optics, Lenses & FiltersAiry Disc
The small bright disc surrounded by faint rings that a perfect lens produces from a point source, set by diffraction alone.
Optics, Lenses & FiltersAnamorphic Lens
A lens containing cylindrical elements that squeeze a wide field horizontally onto a standard frame, to be unsqueezed on projection.
Optics, Lenses & FiltersAngle of View
The angular extent of the scene a lens and sensor combination captures, usually quoted across the frame's diagonal.
Optics, Lenses & FiltersAperture Blades
The overlapping leaves inside a lens that form the iris, whose number and shape determine the geometry of the opening.
Optics, Lenses & FiltersApochromatic Lens
A lens corrected to bring three wavelengths of light to a common focus, rather than the two of a conventional achromat.
Optics, Lenses & FiltersAspherical Element
A lens element whose surface departs from a simple sphere, correcting aberrations that spherical glass cannot.
Optics, Lenses & FiltersAstigmatism
An aberration in which lines running radially and tangentially from the frame centre focus at different distances.
Optics, Lenses & FiltersBarrel Distortion
A geometric distortion in which straight lines bow outward from the centre, as if the image were wrapped around a barrel.
Optics, Lenses & FiltersBokeh
The aesthetic character of the out-of-focus areas of an image, as distinct from how much of the image is out of focus.
Optics, Lenses & FiltersCat's-eye Bokeh
The lens-shaped, off-round rendering of out-of-focus highlights near the frame corners, caused by optical vignetting.
Optics, Lenses & FiltersCatadioptric (Mirror) Lens
A long lens that folds its light path with curved mirrors as well as glass, achieving great focal length in a short, light barrel.
Optics, Lenses & FiltersCircular Polarising Filter
A rotating filter that blocks polarised light, cutting reflections from non-metallic surfaces and deepening blue skies.
Optics, Lenses & FiltersClose-up Diopter
A magnifying filter that screws onto the front of a lens to allow closer focusing without losing light.
Optics, Lenses & FiltersComa
An aberration that renders off-axis points of light as asymmetric comet-shaped smears rather than dots.
Optics, Lenses & FiltersDiffraction
The spreading of light waves as they pass the edge of an aperture, which softens the image at small f-numbers.
Optics, Lenses & FiltersDiffraction Limit
The aperture beyond which diffraction, rather than lens design or sensor resolution, becomes the factor limiting sharpness.
Optics, Lenses & FiltersDiffusion Filter
A filter that scatters a small proportion of the light passing through it, lowering contrast and blooming highlights into a soft glow.
Optics, Lenses & FiltersEntrance Pupil
The apparent size and position of the aperture as seen from in front of the lens, which is what the f-number is calculated from.
Optics, Lenses & FiltersExit Pupil
The apparent size and position of the aperture as seen from behind the lens, which governs how light strikes the sensor.
Optics, Lenses & FiltersExtension Tube
A hollow spacer placed between lens and camera that shortens the minimum focus distance and increases magnification.
Optics, Lenses & FiltersField Curvature
A defect in which a lens focuses a flat subject onto a curved surface rather than the flat plane of the sensor.
Optics, Lenses & FiltersFisheye Lens
An ultra-wide lens that deliberately abandons rectilinear projection, bending straight lines to squeeze 180° or more into the frame.
Optics, Lenses & FiltersFluorite Element
An element made of grown calcium fluoride crystal, which has exceptionally low dispersion and enables near-perfect colour correction.