Exposure Value

{
  "aperture": 8,
  "asOf": "2026-10-11T08:40:14.777Z",
  "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.",
  "equivalentPairsAtSameIso": [
    {
      "aperture": 1,
      "exactShutterS": 0.000125,
      "nearestStandardShutter": "1/8000 s"
    },
    {
      "aperture": 1.4,
      "exactShutterS": 0.000245,
      "nearestStandardShutter": "1/4000 s"
    }
  ],
  "ev100": 12.9658,
  "evAtIso": 12.9658,
  "iso": 100,
  "notChecked": [
    "metering of your actual scene (this is the maths of a chosen setting, not a meter reading)",
    "reciprocity failure for very long exposures on film",
    "…1 more"
  ],
  "reasons": [
    "EV = log2(N squared / t), referenced to ISO 100; each ISO doubling subtracts 1 stop.",
    "Equivalent exposures keep the same light: close the aperture one stop and double the shutter time."
  ],
  "shutterS": 0.008,
  "source": "computed locally",
  "suitsLight": "overcast",
  "summary": "f/8 at 1/125 s and ISO 100: EV 12.97 at ISO 100 (suits overcast); EV at the chosen ISO 12.97.",
  "verdict": "COMPUTED"
}

# bash or zsh: see the payment challenge. Nothing is charged.
curl -sS -g -i 'https://photo-calc.x402tookit.com/exposure-value?aperture=8&iso=100&shutter=1%2F125'

# 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/exposure-value?aperture=8&iso=100&shutter=1%2F125' \
  | 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%2Fexposure-value
const res = await pay("https://photo-calc.x402tookit.com/exposure-value?aperture=8&iso=100&shutter=1%2F125");
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/exposure-value?aperture=8&iso=100&shutter=1%2F125")
    print(res.status_code, res.text)