Looney 11 lunar exposure calculator
For a full Moon at ISO 100 and 1/100 second, the Looney 11 rule gives f/11: enter any ISO and shutter speed and get the aperture that keeps the Moon equally bright, adjusted for gibbous, quarter or crescent phases. Free in your browser.
- Free
- Runs in your browser
- No sign-up
- Your data stays on your device
Run — free
Worked example
- Iso
- 100
- Shutter speed
- 0.01
- Shutter label
- 1/100 f-number
- Phase
- Full
- Phase n
- 11
- Aperture
- 11
The Looney 11 rule is the lunar cousin of Sunny 16: for a bright full Moon, set aperture to f/11 and shutter speed to about one over your ISO—so ISO 100 pairs with roughly 1/100 second, ISO 200 with 1/200 second, and so on. This Looney 11 lunar exposure calculator lets you pick any positive ISO and any shutter time (decimal seconds or camera-style fractions such as 1/125), then returns the matching f-number that keeps the same moon brightness under the classic rule. Optional phase scales open the aperture for gibbous, quarter, crescent, and earthshine targets the way field tables teach.
What the Looney 11 rule is and how the math works
Photographers often underexpose or overexpose the Moon because the bright disk fools matrix metering into darkening the whole frame or because handheld “guesses” ignore how ISO and shutter trade stops. Looney 11 is a simple photometric rule of thumb for the full Moon under clear dark skies: fix the aperture at f/11 and set shutter speed to the reciprocal of the ISO value. That single pair defines a constant exposure for the lunar surface brightness assumed by the rule.
Algebraically, the product of ISO and shutter time (in seconds) is one at the classic point—ISO one hundred times one one-hundredth of a second equals one—so any other pair with the same product keeps the same total exposure when the aperture stays f/11. When you hold ISO and shutter fixed and solve for aperture instead, the square-root form appears: aperture equals eleven times the square root of ISO times shutter.
Doubling shutter time at fixed ISO is one stop more light, so the f-number must rise by the square root of two to compensate; doubling ISO at fixed shutter is the same stop relationship. Phase tables used in teaching often keep shutter equal to one over ISO and open the diaphragm for thinner moons—roughly f/8 for gibbous, f/5.6 for quarter, f/4 for crescent, and f/2.8 when you are chasing earthshine on the dark limb.
This calculator applies those phase reference numbers as N_phase in the same square-root formula so one equation covers full and partial moons. It is not a substitute for a spot meter through haze, smoke, or heavy twilight, and it does not model atmospheric extinction or your particular teleconverter transmission; it is the deterministic rule people search for when they type “Looney 11 calculator” before a night shoot.
Field tips, related tools, and when not to use this
Start from the classic full-moon pair: set shutter near one over ISO at f/11, then let the calculator rebalance when you need a faster shutter to freeze atmospheric shimmer on a long telephoto or a slower shutter on a sturdy mount. For thinner phases, pick gibbous through earthshine so N_phase opens correctly without mental stop counting under cold gloves. Crop sensors and teleconverters do not change the Looney 11 aperture equation itself—they change framing and light transmission—so meter or inspect histograms if you stack converters.
Prefer this landing when the search intent is lunar exposure from the Looney 11 rule; use the separate NPF rule and five-hundred-rule capabilities when the subject is star trailing on fixed tripods, exposure-value tools when you already know aperture shutter and ISO and only want EV, and ND filter shutter calculators when a density filter—not the Moon—drives the time stretch. Keep optical values inside the published absolute range so square roots cannot overflow into non-finite results.
Prefer sending numbers rather than pre-formatted strings when you control the client; string numbers and fraction shutters are accepted when they match a strict finite pattern.
What you can do with it
Full-moon telephoto planning
Before a bright full Moon rise, enter your working ISO and the shutter you can freeze on a long lens to read the Looney 11 f-number and nearest standard stop.
Phase-aware field tables
Generate gibbous, quarter, and crescent aperture tables from the same ISO and shutter so assistants share one printable card for the week’s lunar phase.
FAQ
What is the Looney 11 rule for moon photography?
For a bright full Moon, set aperture to f/11 and shutter speed to about 1/ISO (for example ISO 100 → 1/100 s). This calculator solves the equivalent aperture when you choose any ISO and shutter pair.
How does the calculator use ISO and shutter speed?
For full moon N_phase is 11; thinner phases use 8, 5.6, 4, or 2.8. Fraction shutters like "1/125" are accepted.
What moon phases are supported?
Optional phase values are full (default), gibbous, quarter, crescent, and earthshine.
Why is there a nearest standard aperture?
Lenses are marked in full or third stops.
Is the Looney 11 lunar exposure calculator free?
The browser tool is free and runs locally.
Related tools
For developers — API access
Everything on this page is available programmatically. This section is for teams who want to wire it into their own systems; everyone else can just use the tool above.
API endpoint
Prefer to automate it? One authenticated POST creates the task; the result comes back by webhook or a signed link. The same capability also runs here on the web, by email and from Telegram — and soon from our app too.
Call it from your stack
curl -X POST https://api.kit.forhosting.com/hobby/photo-looney11-moon \
-H "Authorization: Bearer $KIT_KEY" \
-H "Content-Type: application/json" \
-d '{"iso":100,"shutter_speed":0.01}'const res = await fetch("https://api.kit.forhosting.com/hobby/photo-looney11-moon", {
method: "POST",
headers: {
"Authorization": `Bearer ${process.env.KIT_KEY}`,
"Content-Type": "application/json"
},
body: JSON.stringify({
"iso": 100,
"shutter_speed": 0.01
})
});
const { task_id } = await res.json();import os, requests
res = requests.post(
"https://api.kit.forhosting.com/hobby/photo-looney11-moon",
headers={"Authorization": f"Bearer {os.environ['KIT_KEY']}"},
json={
"iso": 100,
"shutter_speed": 0.01
},
)
task_id = res.json()["task_id"]<?php
$res = file_get_contents("https://api.kit.forhosting.com/hobby/photo-looney11-moon", false, stream_context_create([
"http" => [
"method" => "POST",
"header" => "Authorization: Bearer " . getenv("KIT_KEY") . "\r\nContent-Type: application/json",
"content" => '{"iso":100,"shutter_speed":0.01}',
],
]));
$task = json_decode($res, true);body := bytes.NewBufferString(`{"iso":100,"shutter_speed":0.01}`)
req, _ := http.NewRequest("POST", "https://api.kit.forhosting.com/hobby/photo-looney11-moon", body)
req.Header.Set("Authorization", "Bearer "+os.Getenv("KIT_KEY"))
req.Header.Set("Content-Type", "application/json")
res, _ := http.DefaultClient.Do(req)Example request
{
"iso": 100,
"shutter_speed": 0.01
}Example response
{
"task_id": "tsk_a1b2c3d4e5f6a1b2c3d4e5f6",
"type": "hobby.photo_looney11_moon",
"status": "queued",
"_links": {
"result": "/tasks/tsk_…/result"
}
}The API is asynchronous: the call returns a task_id immediately and the result arrives by webhook. Polling is capped at 1 req/s per task.
Pricing
Published price — no tokens, no invented credits. A failed task is never charged.
Errors
| HTTP | Code | Meaning |
|---|---|---|
401 | unauthorized | Missing or invalid API key. |
402 | insufficient_balance | Your balance doesn't cover the task price. |
404 | unknown_type | That task type doesn't exist. |
429 | rate_limited | Too many requests. Use the webhook instead of polling. |
Technical notes
How to call the API and what comes back
Shutter accepts decimal values such as zero point zero one or fraction strings such as one slash one hundred; ISO must be greater than zero. Classic checks include ISO one hundred and shutter one one-hundredth of a second yielding aperture eleven on full phase, or ISO two hundred and one two-hundredth yielding the same classic full-moon point. Wire the free browser form for field math, then call the identical contract from scripts when you bulk-build exposure tables or lesson answer keys. Send a JSON body with two required finite positive numbers: iso (aliases sensitivity, asa, s, iso_speed) and shutter_speed in seconds (aliases shutter, t, exposure_time, speed, time). Optionally send phase as one of full, gibbous, quarter, crescent, or earthshine—aliases include moon_phase and lunar_phase—and the solver maps common synonyms like first_quarter or waxing_crescent. Missing fields, zeros, negatives, NaN, Infinity, and unknown phase labels return invalid_input and are never charged. Absolute magnitudes stay within the published one-trillion guard so intermediate products remain finite in IEEE double precision on the Worker and in the browser. On success the response echoes rounded iso and shutter_speed, a shutter_label preferring reciprocal form when clean, the resolved phase and phase_n reference, aperture as a precise f-number with aperture_label, nearest_standard_aperture and its label for common full stops, looney_11_shutter equal to one over ISO with a matching label, stops_from_f11 for how many stops the exact aperture sits from f/11, unit set to f-number, plus formula, message, and an ordered steps array of substitutions. Pricing for successful API calls is the published base of $0.002 per item; validation failures do not consume prepaid balance.
Field tips, related tools, and when not to use this
If your lens only has full stops, trust nearest_standard_aperture and refine with a quick chimping pass because lunar albedo and local haze still vary. Round-trip checks are easy: recompute N_phase times the square root of ISO times shutter by hand and confirm it equals aperture within the same twelve-decimal rounding the Worker applies.
Integration use cases
Classroom and app fixtures
Build deterministic answer keys and regression fixtures for photography courses and moon-exposure apps that teach Looney 11 with stable JSON steps.