# Photography Calculators

Exposure value and trades, depth of field, field of view, crop factor, ND filters, handheld and star-trail rules, print size, sunny 16, flash and time-lapse.

## How to pay

Machine-payable over x402. USDC on: Base (eip155:8453), Solana (solana:5eykt4UsFv8P8NJdTREpY1vzqKqZKvdp), Polygon (eip155:137), Arbitrum One (eip155:42161).
No accounts. No API keys. No signup. The paying wallet is the account.

## Machine-readable

- OpenAPI: https://photo-calc.x402tookit.com/openapi.json
- x402 manifest: https://photo-calc.x402tookit.com/.well-known/x402
- Catalog (free): https://photo-calc.x402tookit.com/catalog
- Health (free): https://photo-calc.x402tookit.com/health
- Uptime (free): https://photo-calc.x402tookit.com/uptime

## Endpoints (11)

### GET /crop-factor — $0.02
Crop factor of a sensor, with the full-frame equivalent focal length, aperture and ISO for a lens, or a custom sensor size.
Params: sensor?: string, widthMm?: number, heightMm?: number, focalMm?: number, aperture?: number, iso?: number
Example: https://photo-calc.x402tookit.com/crop-factor?sensor=micro-four-thirds&focalMm=25&aperture=1.8&iso=400

### GET /depth-of-field — $0.02
Depth of field from focal length, aperture, distance and sensor: near and far limits, total depth and hyperfocal distance.
Params: focalMm: number, aperture: number, distanceM: number, sensor?: string, cocMm?: number
Example: https://photo-calc.x402tookit.com/depth-of-field?focalMm=50&aperture=8&distanceM=3&sensor=full-frame&cocMm=0.03

### GET /exposure-trade — $0.02
Hold exposure constant: change one setting (aperture, shutter or ISO) and get the other two compensations, in stops.
Params: aperture: number, shutter: string, iso: number, newAperture?: number, newShutter?: string, newIso?: number
Example: https://photo-calc.x402tookit.com/exposure-trade?aperture=5.6&shutter=1%2F125&iso=100&newAperture=11

### GET /exposure-value — $0.02
Exposure value (EV) from aperture, shutter speed and ISO, the light level it suits, and equivalent aperture and shutter pairs.
Params: aperture: number, shutter: string, iso?: number
Example: https://photo-calc.x402tookit.com/exposure-value?aperture=8&shutter=1%2F125&iso=100

### GET /field-of-view — $0.02
Horizontal, vertical and diagonal angle of view for a lens and sensor, and the width and height of scene covered at a distance.
Params: focalMm: number, sensor?: string, distanceM?: number
Example: https://photo-calc.x402tookit.com/field-of-view?focalMm=50&sensor=full-frame&distanceM=10

### GET /flash-guide-number — $0.02
Flash guide-number maths: range for an aperture and ISO, or the aperture needed for a distance, in metres and feet.
Params: guideNumber: number, iso?: number, aperture?: number, distanceM?: number
Example: https://photo-calc.x402tookit.com/flash-guide-number?guideNumber=58&aperture=8

### GET /nd-filter — $0.02
ND filter maths: convert between ND factor, stops and optical density, and get the new shutter time with the filter on.
Params: shutter: string, stops?: number, factor?: number, density?: number
Example: https://photo-calc.x402tookit.com/nd-filter?shutter=1%2F60&stops=10

### GET /print-size — $0.02
Print size from image pixels at a DPI, or the pixels and megapixels needed for a print size; with viewing-distance advice.
Params: widthPx?: integer, heightPx?: integer, dpi?: number, printWidthIn?: number, printHeightIn?: number
Example: https://photo-calc.x402tookit.com/print-size?widthPx=6000&heightPx=4000&dpi=300

### GET /shutter-rule — $0.02
Minimum handheld shutter speed (reciprocal rule) and the longest star-point exposure by the 500 rule and the NPF rule.
Params: focalMm: number, sensor?: string, aperture?: number, pixelPitchUm?: number, declinationDeg?: number, stabilisationStops?: number
Example: https://photo-calc.x402tookit.com/shutter-rule?focalMm=24&sensor=full-frame&aperture=2.8&pixelPitchUm=4.3

### GET /sunny-16 — $0.02
The sunny-16 rule: starting aperture and shutter speed for sun, cloud or shade at your ISO, with the exposure value it implies.
Params: weather: string, iso?: number
Example: https://photo-calc.x402tookit.com/sunny-16?weather=sunny&iso=200

### GET /timelapse-calc — $0.02
Time-lapse planner: give any two of interval, shooting time and clip length to get the rest, frame count and storage.
Params: intervalS?: number, shootMinutes?: number, clipSeconds?: number, fps?: number, fileMb?: number
Example: https://photo-calc.x402tookit.com/timelapse-calc?intervalS=5&shootMinutes=120&fps=24

## Terms

Results are computed locally from standard optics and exposure formulas, provided as is, for ideal lenses and thin-lens approximations. Real lenses vary (focal length changes when focusing, diffraction, distortion) and depth-of-field depends on viewing assumptions. Treat results as planning aids, not guarantees.