Shutter Rule

{
  "asOf": "2026-10-11T08:40:16.090Z",
  "cropFactor": 1,
  "degraded": false,
  "disclaimer": "Screening signal computed from the named public source. Not financial, legal or investment advice; provided as is. Verify at the source before acting.",
  "equivalentFocalMm": 24,
  "focalMm": 24,
  "handheldMinShutter": "1/24 s",
  "handheldMinShutterS": 0.041667,
  "handheldWithStabilisation": "1/24 s",
  "handheldWithStabilisationS": 0.041667,
  "notChecked": [
    "your steadiness, camera weight and shutter shock (the reciprocal rule is a guide)",
    "high-resolution sensors, which show motion blur sooner than the rules suggest",
    "…2 more"
  ],
  "npfAtDeclinationS": 9.458,
  "npfS": 9.458,
  "reasons": [
    "Reciprocal rule: shutter at least 1 / (focal length x crop factor). Add stabilisation stops to slow it.",
    "500 rule: stars stay points for 500 / equivalent focal length seconds (too generous on high-resolution sensors); NPF = (35 x N + 30 x pixel pitch in um) / focal length."
  ],
  "sensor": "full-frame",
  "source": "computed locally",
  "starRule400S": 16.67,
  "starRule500FullFrameS": 20.83,
  "starRule500S": 20.83,
  "summary": "24 mm on full-frame (24 mm equivalent): handheld at 1/24 s or faster; 500 rule for stars 20.8 s. NPF rule: 9.46 s (9.46 s at declination 0 deg).",
  "verdict": "COMPUTED"
}

# bash or zsh: see the payment challenge. Nothing is charged.
curl -sS -g -i 'https://photo-calc.x402tookit.com/shutter-rule?aperture=2.8&focalMm=24&pixelPitchUm=4.3&sensor=full-frame'

# x402 v2 sends the challenge base64-encoded in the PAYMENT-REQUIRED header (v1 sends it in the body).
# To read the header:
curl -sS -g -o /dev/null -D - 'https://photo-calc.x402tookit.com/shutter-rule?aperture=2.8&focalMm=24&pixelPitchUm=4.3&sensor=full-frame' \
  | grep -i '^payment-required:' | cut -d' ' -f2 | tr -d '\r' | base64 --decode

// npm i @x402/fetch @x402/evm viem
import { wrapFetchWithPayment, x402Client } from "@x402/fetch";
import { registerExactEvmScheme } from "@x402/evm/exact/client";
import { privateKeyToAccount } from "viem/accounts";

// Pays at most $0.02 per call.
const client = new x402Client().setSpendControls({ maxAmountPerPayment: "$0.02" });
registerExactEvmScheme(client, { signer: privateKeyToAccount(process.env.EVM_PRIVATE_KEY) });
const pay = wrapFetchWithPayment(fetch, client);

// Not sure it's safe to pay? ToolVet checks it first for $0.005. Pay for that from a separate
// client: this one is capped at $0.02 per payment. GET https://toolvet.app/api/v1/check?url=https%3A%2F%2Fphoto-calc.x402tookit.com%2Fshutter-rule
const res = await pay("https://photo-calc.x402tookit.com/shutter-rule?aperture=2.8&focalMm=24&pixelPitchUm=4.3&sensor=full-frame");
console.log(res.status, await res.text());

# pip install "x402[requests,evm]"
import os
from eth_account import Account
from x402 import x402ClientSync
from x402.http.clients import x402_requests
from x402.mechanisms.evm import EthAccountSigner
from x402.mechanisms.evm.exact.register import register_exact_evm_client

# Pays at most $0.02 per call.
client = x402ClientSync().set_spend_controls({"max_amount_per_payment": "$0.02"})
register_exact_evm_client(client, EthAccountSigner(Account.from_key(os.environ["EVM_PRIVATE_KEY"])))

with x402_requests(client) as session:
    res = session.get("https://photo-calc.x402tookit.com/shutter-rule?aperture=2.8&focalMm=24&pixelPitchUm=4.3&sensor=full-frame")
    print(res.status_code, res.text)