| ADC | Assistant/Director of Photography — a crew role designation |
| Altitude | The angle of a celestial body above the horizon, measured in degrees (0° = horizon, 90° = directly overhead) |
| Astronomical Twilight | Twilight when the sun is between 12° and 18° below the horizon; sky is almost completely dark |
| Azimuth | The compass direction of a celestial body, measured in degrees clockwise from North (0° = North, 90° = East, 180° = South, 270° = West) |
| Blue Hour | The period just before sunrise or just after sunset when indirect sunlight creates a blue cast — popular for architecture and cityscape photography |
| Booking | A confirmed (or tentative) photography engagement in Apex Lucis |
| Call Sheet | A document listing the day’s shooting schedule: times, locations, crew, and planned shots |
| Circle of Confusion | How much blur still reads as sharp in a print. It sets where depth of field begins and ends, and differs by sensor size |
| Civil Twilight | Twilight when the sun is between 0° and 6° below the horizon; bright enough to work without artificial light |
| Contact | A person in your professional network who you work with (crew, talent, vendor) — distinct from a Client |
| Crew Roster | The list of people assigned to a specific booking |
| Field of View | How much of a scene a lens takes in, in degrees. It depends on the focal length and the size of the sensor behind it, and on nothing else |
| GBIF | Global Biodiversity Information Facility — a database of biodiversity observations used for wildlife species data |
| Galactic Centre | The central region of the Milky Way galaxy, which rises and sets at specific times/directions depending on location and date |
| Golden Hour | The period shortly after sunrise or before sunset when sunlight is warm and directional — widely considered the best light for photography |
| Hyperfocal Distance | Focus here and everything from half this distance to infinity is sharp. The setting for a landscape where the foreground matters as much as the hills |
| IAP | In-App Purchase — the mechanism used to purchase an Apex Lucis Pro subscription |
| Illumination | The percentage of the moon’s visible face that is lit by the sun (0% = new moon, 100% = full moon) |
| Invoice | A financial document requesting payment from a client for photography services |
| Julian Day | A continuous count of days used in astronomical calculations, starting from 1 January 4713 BC |
| KPI | Key Performance Indicator — a measurable business metric |
| Kp | A 0–9 scale of geomagnetic activity. The higher it is, the further from the poles the aurora reaches |
| Lead | A potential client enquiry that has not yet been converted to a booking |
| Line Item | One charge on an invoice — a description, a quantity and a price. An invoice’s amount is the total of its lines |
| Margin | What a shoot made: everything charged for it, less what it cost to put on |
| Markup | What you add on top of a cost when charging it to a client — the difference between a £750 studio hire and the £900 billed for it |
| Mileage Rate | The cost-per-mile (or km) used to calculate travel expense claims |
| ND Filter | A neutral density filter — dark glass that cuts the light without changing its colour, so the shutter can stay open longer. Measured in stops |
| NPF Rule | The longest exposure that still records stars as points rather than streaks. Unlike the older 500 rule it accounts for aperture and pixel size |
| Nautical Twilight | Twilight when the sun is between 6° and 12° below the horizon; the horizon is still distinguishable at sea |
| New Moon | The lunar phase when the moon is not illuminated and not visible at night — optimal for Milky Way photography |
| P&L | Profit and Loss — a financial statement summarising revenue, expenses, and net profit |
| Package | A reusable pricing template defining a type of shoot and its base price |
| Permit | Official permission to photograph in a specific location, particularly for commercial or drone use |
| Pipeline | The sequence of stages a lead passes through before becoming a booking (Enquiry → Contacted → Quoted → Won) |
| Pixel Pitch | How far apart a sensor’s photosites sit. A denser sensor shows star movement sooner, which is why the star calculators need your camera’s resolution |
| Recharge | Billing a cost you carried for a shoot — studio hire, a second shooter, mileage — on to the client as a line on their invoice |
| Recovered | A recharged cost that has been billed: the invoice carrying it has been sent |
| Reimbursable | A cost marked as one the client will pay back. It stays outstanding until the invoice carrying it is sent |
| Shoot Score | Apex Lucis’s composite rating (0–100) of current or forecast photographic conditions |
| Shot List | A pre-planned list of individual images to capture on a shoot |
| Stop | A doubling or halving of light. One stop of ND doubles the exposure time, so ten stops is a thousand times longer, not ten |
| Studio | A hire space you describe once — its room, specifications, rate and equipment — so every booking of it after that is just a date |
| Studio Booking | One hire of a studio: the date, the times, what it cost and what was hired for it |
| Tidal Extreme | A high tide or low tide — the peak and trough of a tidal cycle |
| Transit | The moment when a celestial body crosses the meridian (due south in the northern hemisphere) — its highest point in the sky |
| Trip | A planned travel arrangement associated with a shoot, including accommodation and travel legs |
| VAT | Value Added Tax — a UK/EU consumption tax applied to invoices. Apex Lucis supports configurable tax labels for other regions (GST, Tax, etc.) |
| WeatherKit | Apple’s native weather forecast API used by Apex Lucis for weather data |