{"success":true,"version":"v1","request":{"tool":"get_calculator_schema","calculator_id":"exposure-value"},"result":{"entity_type":"calculator","id":"exposure-value","calculator_id":"exposure-value","canonical_url":"https://tttkmbb.com/photography/exposure-value","name":"Exposure Value Calculator","title":"Exposure Value (EV) Calculator – EV, EV100 and Scene Illuminance from Aperture, Shutter and ISO","category":"photography","category_name":"Photography & Optics","tool_name":"calculate_exposure_value","featured_mcp_tool":false,"description":"Computes the exposure value EV = log2(N²/t) of a camera setting, the ISO-100 normalised light value EV100, an illuminance estimate in lux (incident-meter calibration C = 250) and a description of the lighting the settings correspond to.","use_when":"You want to express aperture, shutter and ISO as a single exposure number, estimate how bright a scene is, or check settings against the Sunny 16 rule.","do_not_use_when":"You want to translate one setting into another with the same exposure (use equivalent-exposure) or to work out a long exposure with an ND filter (use nd-filter-exposure).","inputs":[{"name":"aperture_f","label":"Aperture (f-number)","type":"number","required":true,"min":0.5,"max":128,"description":"Lens f-number, e.g. 2.8 for f/2.8.","example":16},{"name":"shutter_seconds","label":"Shutter speed","type":"number","unit":"s","required":true,"max":86400,"exclusive_min":0,"description":"Exposure time in seconds. Enter fractions as decimals: 1/125 s = 0.008, 1/60 s = 0.016667, 1/1000 s = 0.001.","example":0.008},{"name":"iso","label":"ISO","type":"number","required":false,"default":100,"min":1,"max":10000000,"description":"ISO sensitivity setting (100, 200, 400, ...).","example":100}],"outputs":[{"name":"ev","label":"Exposure value","type":"number","unit":"EV","decimals":1,"description":"log2(aperture_f² / shutter_seconds), independent of ISO."},{"name":"ev100","label":"EV at ISO 100 (light value)","type":"number","unit":"EV","decimals":1,"description":"ev − log2(iso / 100): the scene brightness these settings expose correctly."},{"name":"illuminance_lux_estimate","label":"Illuminance estimate","type":"number","unit":"lx","decimals":2,"description":"2.5 × 2^ev100 lux, the incident-light meter relation with calibration constant C = 250 (average subject reflectance assumed)."},{"name":"lighting_description","label":"Typical lighting","type":"string","decimals":4,"description":"Scene type that corresponds to ev100 (EV 15 bright sun, EV 12–13 overcast, EV 7–8 bright indoor, EV 4–6 dim indoor, EV ≤ 0 night)."},{"name":"shutter_text","label":"Shutter speed (text)","type":"string","decimals":4,"description":"The shutter speed as a conventional fraction, e.g. '1/125 s'."}],"input_schema":{"type":"object","properties":{"aperture_f":{"description":"Lens f-number, e.g. 2.8 for f/2.8.","type":"number","minimum":0.5,"maximum":128,"examples":[16]},"shutter_seconds":{"description":"Exposure time in seconds. Enter fractions as decimals: 1/125 s = 0.008, 1/60 s = 0.016667, 1/1000 s = 0.001. Unit: s.","type":"number","maximum":86400,"exclusiveMinimum":0,"examples":[0.008],"x-unit":"s"},"iso":{"description":"ISO sensitivity setting (100, 200, 400, ...).","type":"number","minimum":1,"maximum":10000000,"default":100,"examples":[100]}},"additionalProperties":false,"required":["aperture_f","shutter_seconds"]},"output_schema":{"type":"object","properties":{"ev":{"description":"log2(aperture_f² / shutter_seconds), independent of ISO. Unit: EV.","type":"number","x-unit":"EV"},"ev100":{"description":"ev − log2(iso / 100): the scene brightness these settings expose correctly. Unit: EV.","type":"number","x-unit":"EV"},"illuminance_lux_estimate":{"description":"2.5 × 2^ev100 lux, the incident-light meter relation with calibration constant C = 250 (average subject reflectance assumed). Unit: lx.","type":"number","x-unit":"lx"},"lighting_description":{"description":"Scene type that corresponds to ev100 (EV 15 bright sun, EV 12–13 overcast, EV 7–8 bright indoor, EV 4–6 dim indoor, EV ≤ 0 night).","type":"string"},"shutter_text":{"description":"The shutter speed as a conventional fraction, e.g. '1/125 s'.","type":"string"}}},"formula":"ev = log2(aperture_f² / shutter_seconds); ev100 = ev − log2(iso / 100); illuminance_lux = 250 × 2^ev / iso = 2.5 × 2^ev100","method":"EV definition per the APEX system; the lux relation follows the ISO 2720 incident-meter equation EV = log2(E·S / C) with C = 250 lx·s, so it assumes a correctly exposed scene of average reflectance and is only an estimate (±1 EV).","sources":[{"name":"Wikipedia – Exposure value","url":"https://en.wikipedia.org/wiki/Exposure_value","type":"reference","retrieved_at":"2026-09-24"},{"name":"Wikipedia – Light meter","url":"https://en.wikipedia.org/wiki/Light_meter","type":"reference","retrieved_at":"2026-09-24"},{"name":"Wikipedia – Sunny 16 rule","url":"https://en.wikipedia.org/wiki/Sunny_16_rule","type":"reference","retrieved_at":"2026-09-24"}],"freshness":{"type":"static","max_age_seconds":null,"note":"Deterministic formula with fixed constants; results never go stale. Inputs supplied by the caller determine the output."},"examples":[{"name":"Sunny 16: f/16, 1/125 s, ISO 100","inputs":{"aperture_f":16,"shutter_seconds":0.008,"iso":100},"expected":{"ev":15,"ev100":15,"illuminance_lux_estimate":80000,"lighting_description":"Bright or hazy sun with distinct shadows (EV 15, Sunny 16 rule)"},"url":"https://tttkmbb.com/api/v1/calculate/exposure-value?aperture_f=16&shutter_seconds=0.008&iso=100"},{"name":"Indoor: f/2.8, 1/60 s, ISO 400","inputs":{"aperture_f":2.8,"shutter_seconds":0.016667,"iso":400},"expected":{"ev":8.9,"ev100":6.9,"lighting_description":"Bright indoor lighting: offices, shops, well-lit rooms (EV 7–8)"},"url":"https://tttkmbb.com/api/v1/calculate/exposure-value?aperture_f=2.8&shutter_seconds=0.016667&iso=400"}],"faq":[{"q":"What is the difference between EV and EV100?","a":"EV only combines aperture and shutter. EV100 also removes the ISO, so it describes the light in the scene: f/2.8 at 1/60 s is EV 8.9 at any ISO, but at ISO 400 it exposes an EV100 6.9 scene correctly."},{"q":"Why is the lux value only an estimate?","a":"Camera meters read reflected light and are calibrated for mid-grey subjects; the conversion assumes that and uses C = 250, while meter makers use constants between 240 and 340, so real illuminance can differ by about ±1 EV."},{"q":"How do I enter 1/250 s?","a":"As a decimal: 1/250 = 0.004 s. Common values: 1/1000 = 0.001, 1/500 = 0.002, 1/125 = 0.008, 1/60 = 0.016667, 1/30 = 0.033333."}],"tags":["exposure value","ev calculator","light value","sunny 16","lux","aperture shutter iso"],"related":[{"calculator_id":"equivalent-exposure","reason":"Find other aperture/shutter/ISO combinations with the same exposure."},{"calculator_id":"nd-filter-exposure","reason":"Shutter speed after adding a neutral-density filter."},{"calculator_id":"flash-guide-number","reason":"Aperture or distance for a flash from its guide number."}],"links":{"html":"https://tttkmbb.com/photography/exposure-value","markdown":"https://tttkmbb.com/photography/exposure-value.md","json":"https://tttkmbb.com/photography/exposure-value.json","api":"https://tttkmbb.com/api/v1/calculate/exposure-value","schema":"https://tttkmbb.com/api/v1/calculators/exposure-value","openapi":"https://tttkmbb.com/openapi.json","mcp":"https://tttkmbb.com/mcp"},"version":"v1","updated_at":"2026-09-24"},"timestamp":"2026-09-24T03:44:32Z"}