Flash photography glossary.
Plain-language definitions, the distinctions that matter, and a free tool to put each concept into practice.
- Ambient light
Existing continuous light in the scene, such as sunlight or room lighting. It may reach the subject and background at different levels.
Try: Flash & ambient coach →- Aperture / f-stop
The lens opening expressed as an f-number. At fixed ISO, one stop down needs twice the illumination for the same exposure; the f-number increases by √2.
Try: Flash power calculator →- Apparent source size
The angle a light-emitting surface occupies from the subject. Both physical size and distance affect the shadow transition.
Try: Softbox size & placement →- Catchlight
A reflection visible in the eye. It can suggest source shape and position, but does not reliably count every light in a finished photograph.
Try: Photo → lighting plan →- Complete-pulse capture
A condition in which the camera records essentially the whole flash pulse. Many simple flash-power equations assume it remains unchanged.
Try: Sony a9 III timing calculator →- Exposure stop
A factor of two in exposure or illumination. +1 stop doubles the amount; −1 stop halves it. Specify whether the change refers to light output, camera exposure or a meter reading.
Try: Flash power calculator →- Feathering
Aiming a modifier so the subject uses a different part of its beam. It can change coverage, spill and exposure; measure the actual result.
Try: Grid & modifier calibration →- Fill light
A contribution used to control shadows. It may come from a flash, ambient, a reflector or the room, and it can also reach the brighter side.
Try: Lighting ratio calculator →- Flash duration: t0.1 and t0.5
Pulse-duration measurements taken at different fractions of peak output. They describe different thresholds; neither alone establishes a camera timing offset or complete pulse shape.
Try: Sony a9 III timing calculator →- Flash percentage
The fraction of combined exposure attributed to flash for the selected meter conditions. It depends on the shutter used for ambient and is not a flash-power percentage.
Try: Flash & ambient balance →- Flash power setting
A manual output setting such as 1/16 or 1/8. Moving from 1/16 to 1/8 nominally doubles energy; the captured result must remain linear for a one-stop prediction.
Try: Flash power calculator →- Global shutter
A sensor exposure method that exposes the image simultaneously. A short exposure can still miss part of a flash pulse.
Try: Sony a9 III timing calculator →- Grid
A beam-control accessory that limits light in some directions. Its exposure loss and coverage depend on the actual grid, modifier, aim and distance.
Try: Grid & modifier calibration →- High-speed sync (HSS)
A compatible flash mode that extends emission over focal-plane shutter travel. Meter or test at the actual shutter and mode instead of assuming normal-sync output.
Try: ND exposure calculator →- Incident metering
Measurement of light arriving at a location. Receptor position, orientation and dome configuration are part of the measurement method. It does not directly measure surface reflectance.
Try: Flash power calculator →- Inverse-square law
For a point source with fixed intensity and surface orientation, illumination changes inversely with squared distance. Doubling distance gives one quarter the illumination, or −2 stops.
Try: Light placement calculator →- Key light
The main source shaping the subject in a proposed setup. “Main” describes its role and does not always mean the highest power fraction on a flash display.
Try: Photo → lighting plan →- Lighting ratio
A comparison of specified light contributions or locations. State whether you mean isolated key-to-fill or bright-to-shadow contrast; those numbers need not match.
Try: Lighting ratio calculator →- Meter tenths
Fractions of an exposure stop displayed beside a base aperture. f/8 + 0.3 stop means 8 × 2^(0.3/2), about f/8.88, not f/8.3.
Try: Flash power calculator →- Neutral-density filter
A filter that attenuates light reaching the camera. A lens ND affects both flash and ambient; include any compensating aperture or ISO change.
Try: ND exposure calculator →- Negative fill
Using an absorbent surface or removing a reflection to reduce light returning into shadows. It cannot subtract direct illumination already reaching the subject.
Try: Light spill mapper →- Reflected metering
Measurement of light returning from a surface. Its reading depends on illumination, reflectance and viewing geometry, unlike an incident reading at that surface.
Try: Subject highlight calibration →- Spill
Light reaching an area where it is unwanted. A power change affects all regions receiving that source, so independent tonal changes may require geometry or beam control.
Try: Light spill mapper →- Flash timing offset
An adjustment to firing relative to the camera exposure. On the Sony a9 III, the Flash Timing Setting advances firing; shutter duration alone does not establish its best value.
Try: Sony a9 III timing calculator →
Published by DNA Premium Portraits. Definitions and examples use the same assumptions as the linked tools. Updated .