Browse All 840 Photography Terms A–Z

Reciprocal Rule Exposure & Metering seconds A handholding guideline stating that the slowest safe shutter speed is roughly one over the focal length in use. t ≤ 1 / (focal length × crop factor)

Reciprocity Failure Film, Darkroom & Historic Processes seconds The breakdown of the reciprocity law at very long or very short exposures, where film needs more light than calculation predicts. t_corrected = t^p

Reciprocity Law Exposure & Metering lux-seconds (lx·s) The principle that exposure depends only on the product of light intensity and time, so halving one and doubling the other leaves the result unchanged. H = E × t

Recycle Time Lighting & Flash seconds The interval a flash needs to recharge its capacitor to full power after firing.

Reflected-light Metering Exposure & Metering EV Measuring the light bouncing off a subject toward the camera, which is what every built-in camera meter does.

Reflection Photography Motion, Video & Creative Techniques Using reflective surfaces — water, glass, metal, screens — as a compositional device rather than a nuisance.

Reflector Lighting & Flash stops A panel that bounces existing light back into the shadows, adding fill without a second light source.

Relative Colorimetric Intent Colour & Colour Management A conversion strategy that reproduces in-gamut colours exactly and clips out-of-gamut ones to the nearest reproducible value.

Release Priority Focus & Depth of Field A setting that fires the shutter whenever the button is pressed, regardless of whether focus has been confirmed.

Rembrandt Lighting Lighting & Flash A portrait pattern in which a small triangle of light appears on the shadowed cheek, below the eye.

Rendering Intent Colour & Colour Management The strategy chosen for handling colours that fall outside the destination gamut during a colour space conversion.

Resin-coated Paper Film, Darkroom & Historic Processes g/m² Photographic paper sealed between thin polyethylene layers so chemistry cannot penetrate the base.

Resolving Power Optics, Lenses & Filters lp/mm The finest detail a lens or film can distinguish, traditionally expressed in line pairs per millimetre.

Retrofocus Design Optics, Lenses & Filters A wide-angle design with a negative front group that places the rear element further from the sensor than the focal length would allow.

RGB Histogram Exposure & Metering Three separate histograms, one per colour channel, revealing clipping that a combined luminance histogram would hide.

Rim Light Lighting & Flash f-stops (EV) A light placed behind and to one side of the subject that draws a bright edge along its outline, separating it from the background.

Ring Flash Lighting & Flash GN (guide number) A flash tube arranged in a circle around the lens, producing nearly shadowless frontal light.

Rolling Shutter Artefact Sensors & Digital Capture ms Distortion caused by a sensor being read out progressively, so different parts of the frame record at slightly different times.

Round-trip Editing Files, Metadata & Workflow Sending an image from a catalogue to an external editor and returning the result automatically to the same collection.

Rule of Odds Composition & Visual Design count The observation that an odd number of subjects in a frame usually reads as more settled than an even number.

Rule of Space Composition & Visual Design The guideline that a subject which is moving or looking in a direction should have space in front of it within the frame.

Rule of Thirds Composition & Visual Design A guideline that divides the frame into nine equal parts and suggests placing key elements along those lines or at their intersections. Frame ÷ 3 horizontally and vertically

S-curve Composition & Visual Design A gently reversing curve within a scene that carries the eye through the frame in a sinuous path.

Safelight Film, Darkroom & Historic Processes nm A darkroom lamp emitting only wavelengths to which the material in use is insensitive.

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