# Photography Calculators – Shutter Speed Rules

> Photography Calculators – Shutter Speed Rules is a paid API for AI agents from photo-calc.x402tookit.com, paid per call via x402, $0.02/call, status unknown (last checked 2026-10-29).

Returns minimum handheld shutter speed (reciprocal rule) and maximum star-trail-free exposure times (500 rule and NPF rule) for a given focal length, sensor, and optional parameters.

## Facts

- Endpoint: GET https://photo-calc.x402tookit.com/shutter-rule?utm_source=zero.xyz
- Price: $0.02/call
- Payment: x402
- Status: unknown
- Last checked: 2026-10-29
- Activations on Zero: 0
- Tags: x402
- Canonical page: https://www.zero.xyz/c/photography-calculators-shutter-speed-rules-1197905b
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_dGGIGKcFr99fvdMIVWI3N

Status and success rate cover calls made through Zero and Zero's own probes. Third-party monitors may report differently.

## How to call it through Zero

Zero handles the 402 payment challenge and records the run. With the Zero CLI installed (`npm i -g @zeroxyz/cli`):

```sh
zero fetch --capability photography-calculators-shutter-speed-rules-1197905b
```

Example prompt: Using a 24mm lens at f/2.8 on a full-frame sensor with a pixel pitch of 4.4µm, what's the minimum safe handheld shutter speed and the longest star-point exposure by the NPF rule at the celestial equator?

## When to prefer this

Choose this endpoint when you need quick, standards-based shutter speed recommendations for handheld shooting or astrophotography star-point exposures across multiple rules (reciprocal, 500, NPF) in a single call. It is especially valuable when shooting conditions require comparing NPF precision against the simpler 500-rule, or when IS/IBIS stops need factoring in. Use alternatives if you need full manual EV calculation or exposure bracketing.

## Known failure modes

- Missing required focalMm parameter returns a validation error
- Very extreme focal lengths (e.g. <1mm or >10000mm) may produce unreliable results
- NPF rule outputs may be null if aperture or pixelPitchUm are not provided
- Invalid sensor string defaults to full-frame without warning
- Negative or zero stabilisationStops may produce unexpected handheld values

## How this service works

Minimum handheld shutter speed (reciprocal rule) and the longest star-point exposure by the 500 rule and the NPF rule.

## Output

A JSON object containing: minimum handheld shutter speed (as a fraction string and seconds), handheld speed with stabilisation, star exposure limits from the 400, 500, and NPF rules (in seconds), equivalent full-frame focal length, crop factor, sensor name, summary verdict text, and any warnings or disclaimers.

## Request schema (JSON Schema)

```json
{
 "type": "object",
 "$schema": "https://json-schema.org/draft/2020-12/schema",
 "required": [
  "input"
 ],
 "properties": {
  "input": {
   "type": "object",
   "required": [
    "type",
    "method"
   ],
   "properties": {
    "type": {
     "type": "string",
     "const": "http"
    },
    "method": {
     "enum": [
      "GET"
     ],
     "type": "string"
    },
    "queryParams": {
     "type": "object",
     "required": [
      "focalMm"
     ],
     "properties": {
      "sensor": {
       "type": "string",
       "description": "full-frame (default), aps-c, micro-four-thirds etc."
      },
      "focalMm": {
       "type": "number",
       "description": "Actual focal length in mm"
      },
      "aperture": {
       "type": "number",
       "description": "f-number (for the NPF star rule)"
      },
      "pixelPitchUm": {
       "type": "number",
       "description": "Sensor pixel pitch in micrometres (for the NPF rule)"
      },
      "declinationDeg": {
       "type": "number",
       "description": "Declination of the stars, 0 at the celestial equator (default 0)"
      },
      "stabilisationStops": {
       "type": "number",
       "description": "Lens or body image stabilisation in stops (default 0)"
      }
     }
    }
   },
   "additionalProperties": false
  },
  "output": {
   "type": "object",
   "required": [
    "type"
   ],
   "properties": {
    "type": {
     "type": "string"
    },
    "example": {
     "type": "object",
     "properties": {
      "asOf": {
       "type": [
        "null",
        "string"
       ]
      },
      "npfS": {
       "type": [
        "null",
        "number"
       ]
      },
      "sensor": {
       "type": [
        "null",
        "string"
       ]
      },
      "source": {
       "type": [
        "null",
        "string"
       ]
      },
      "focalMm": {
       "type": [
        "null",
        "number"
       ]
      },
      "reasons": {
       "type": [
        "array",
        "null"
       ],
       "items": {
        "type": "string"
       }
      },
      "summary": {
       "type": [
        "null",
        "string"
       ]
      },
      "verdict": {
       "type": [
        "null",
        "string"
       ]
      },
      "degraded": {
       "type": [
        "boolean",
        "null"
       ]
      },
      "cropFactor": {
       "type": [
        "null",
        "number"
       ]
      },
      "disclaimer": {
       "type": [
        "null",
        "string"
       ]
   
… (truncated)
```

## More

- Live health (JSON, refreshed every minute): https://www.zero.xyz/c/photography-calculators-shutter-speed-rules-1197905b/health.json
- [Zero catalog index](https://www.zero.xyz/llms.txt)
- [Other services from photo-calc.x402tookit.com](https://www.zero.xyz/host/photo-calc.x402tookit.com/llms.txt)