Words

Glossary

43 terms used across the site. Underlined words in entries link here and show a short definition when you hover them; each term lists the pages that use it.

aberration: Any way a lens fails to bring light to a perfect point: blur at the edges, colour fringes, curved or distorted lines. Lens design is the art of cancelling them.
Used in Lens in the camera obscura · Achromatic lens · Abbe, Zeiss & Schott · Cooke triplet · Lenses
angle of view: How wide a scene a lens takes in on a given format. It depends on both the focal length and the size of the film or sensor.
Used in Lenses
aperture: The opening that lets light through a lens. Its size, relative to the focal length, sets how much light reaches the film or sensor and how deep the zone of sharp focus is.
Used in Lens in the camera obscura · Brownie · Light meter · Auto exposure · Canon EOS · Aperture · Exposure
colour filter array: The mosaic of tiny red, green and blue filters over a digital sensor's pixels; most cameras use Bryce Bayer's pattern. Software then rebuilds full colour at every pixel (demosaicing).
Used in Bayer filter
colour temperature: The colour of light described as the temperature of a glowing body, in kelvin: candlelight is about 1,900 K, daylight about 5,500 K, shade bluer still.
Used in Colour
contact print: A print made by laying the negative directly on the paper, so the print is exactly the size of the negative.
crop factor: How much smaller a format's diagonal is than 35mm full frame (43.3 mm). Multiply focal length by it to get the full-frame lens with the same field of view.
Used in 135 film · APS-C sensor · Full-frame digital · Lenses · Formats
demosaicing: Working out a full colour for every pixel from a sensor whose pixels each see only red, green or blue through a colour filter array.
Used in Raw / DNG · Sensors
depth of field: The range of distances that look sharp in a photograph. It gets deeper with a smaller aperture, a shorter lens, a smaller format or a more distant subject.
Used in Four Thirds · Aperture · Exposure
developer: A chemical bath that turns the latent image into visible metallic silver by reducing the exposed silver halide crystals.
Used in Velox paper · Agfacolor Neu · Zone System · Instant photography · Silver
diffraction: The spreading of light as it passes an edge. It sets a limit on sharpness at very small apertures, and on how fine a pinhole image can be.
Used in Aperture
dynamic range: The span between the darkest and brightest tones a film or sensor can record with detail, usually given in stops.
Used in Stacked sensor · Exposure · Sensors
emulsion: The light-sensitive layer of film, plates or paper: crystals of silver halide held in a binder, gelatin since the 1870s.
Used in Gelatin dry plate · Flash powder · Roll film · Lippmann plate · Agfacolor Neu
enlarger: A projector that throws the image of a negative onto paper at a larger size. It let small negatives make big prints.
Used in Velox paper
exposure: The total light that reaches the film or sensor, set by the aperture, the shutter time and the light itself.
Used in Light meter · Exposure
exposure value (EV): One number for every pairing of aperture and shutter speed that gives the same exposure. EV 15 is about sunny daylight at ISO 100; each step is one stop.
Used in Exposure
f-number: Focal length divided by the diameter of the aperture (N = f/D). Each full stop (f/2, f/2.8, f/4…) multiplies N by about 1.41 and halves the light.
Used in Petzval lens · Pinhole · Aperture
fixer: A chemical, usually sodium thiosulfate ('hypo'), that dissolves the silver salts light has not touched, so the image no longer darkens when seen in daylight.
Used in Hypo fixer · Albumen print
focal length: The distance from a lens to the image it forms of something far away, in millimetres. Longer focal lengths magnify more and see a narrower angle.
Used in TTL metering · Lenses
focal-plane shutter: A shutter of two curtains just in front of the film or sensor. The gap between them sweeps across the frame, so lenses need no shutter of their own.
Used in Mechanical shutters · Speed Graphic · Kine Exakta
full frame: A sensor the size of a 35mm film frame, 36 × 24 mm. The name dates from the digital era, when most sensors were smaller.
Used in 35mm cine film · Leica I · Fujifilm
grain: The visible clumps of silver or dye in a film image. Faster films have larger crystals, so they show more grain.
Used in 120 film · 110 film · Film revival · Exposure · Silver
ISO: The standard scale of sensitivity for film and sensors. Doubling the ISO number means half as much light is needed for the same exposure.
Used in Exposure
latent image: The invisible change light makes in silver halide crystals. Development amplifies it, millions of times over, into visible metallic silver.
Used in Light-sensitive silver · Daguerreotype · Calotype · Gelatin dry plate · Silver
leaf shutter: A shutter of thin blades inside the lens that open from the centre and close again. It is quiet and syncs with flash at any speed.
Used in Mechanical shutters · Hasselblad 1600F
lens mount: The fitting that joins interchangeable lenses to a camera body. A maker's mount often outlives many generations of cameras.
megapixel: One million pixels. A sensor's megapixel count measures how many points it samples, not how sharp or good its pictures are.
Used in First digital image
mirrorless: An interchangeable-lens digital camera with no reflex mirror: the sensor feeds an electronic viewfinder or screen directly.
Used in Nikon F · Sony α7
negative: An image with tones reversed (light areas dark) from which any number of positive prints can be made. The word was coined by John Herschel in 1839.
Used in Calotype · Albumen print · Wet collodion
noise: Random speckle in a digital image. Most comes from the uneven arrival of photons (shot noise), so it is worst where little light falls.
Used in Megapixel sensor · Four Thirds · Exposure
orthochromatic: Sensitive to blue and green light but not red. Early plates and many films were orthochromatic, so red lips and skies came out wrong.
Used in Ortho & panchromatic · Silver
panchromatic: Sensitive to all visible colours, including red, so a black-and-white print shows tones close to how the eye sees them.
Used in Ortho & panchromatic · Silver
pentaprism: A five-sided glass prism above an SLR's focusing screen that turns the image right way up and right way round for eye-level viewing.
Used in Pentaprism finder
pixel: One picture element: on a sensor, a single light-collecting photosite; in a file, one sample of colour and brightness.
Used in CCD sensor · CMOS sensor · Aperture · Silver · Sensors
rangefinder: A camera that focuses by lining up two views of the subject in a small window, separate from the lens. The Leica M and Contax are classic examples.
Used in Autofocus
raw file: The sensor's readings saved almost untouched, before demosaicing, white balance and compression, so they can be processed later with more latitude.
Used in Raw / DNG · Colour · Phase One
reciprocity failure: Film's loss of sensitivity in very long or very short exposures, so that halving the light and doubling the time no longer gives the same result.
Used in Exposure
reversal film: Film processed to give a positive image on the film itself, such as a slide, instead of a negative to print from.
shutter speed: How long the shutter lets light reach the film or sensor, such as 1/125 second. Halving it halves the light and freezes faster movement.
Used in Mechanical shutters · Auto exposure · Image stabilisation · Exposure
SLR: Single-lens reflex: a mirror behind the lens sends its image up to the viewfinder, and flips out of the way when the picture is taken, so you see exactly what the lens sees.
Used in Nikon F · Autofocus · Sony α7
stop: A doubling or halving of light. Opening the aperture one stop, slowing the shutter one stop or doubling the ISO all give one stop more exposure.
Used in Zone System · Image stabilisation · Aperture · Exposure
white balance: Correcting for the colour of the light so that white things look white. Digital cameras do it in processing; film needed filters or a different film.
Used in Raw / DNG · Colour
zoom lens: A lens whose focal length can change while the image stays in focus, by moving groups of elements inside it.
Used in Zoom lens