Airy disk diameter calculator
In green light of 550 nm at f/8, the Airy disk is 10.736 µm across: enter wavelength and f-number to see how large diffraction blur gets as you stop down, and compare it with your pixel size. Free in your browser.
- Free
- Runs in your browser
- No sign-up
- Your data stays on your device
Run — free
Worked example
- Wavelength
- 550
- F number
- 8
- Airy diameter
- 10,736
- Airy radius
- 5,368
- Airy factor
- 2.44
When you stop a lens down, depth of field grows but wave optics sets a hard floor on how sharp the finest detail can stay. Light passing a circular aperture forms an Airy disk: a bright central core ringed by faint diffraction rings. The first-null diameter of that disk is d equals 2.44 times wavelength times the working f-number. Photographers use this closed form to compare diffraction blur to pixel pitch, decide when to stop stopping down, and explain soft microcontrast at f/16 or f/22. This Airy disk diameter calculator takes wavelength and f-number, returns diameter and radius, and runs as pure deterministic arithmetic with no network and no model tokens.
Why Airy disk diameter matters for diffraction blur
A circular lens aperture of diameter D focusing monochromatic light of wavelength lambda produces a far-field pattern whose first intensity zero of the circular diffraction integral lies at an angular radius near 1.22 lambda over D from the optical axis. In the focal plane of a system whose working f-number is N equals f over D, that angle maps to a linear radius r equals 1.22 lambda N, so the full first-null diameter is d equals 2.44 lambda N.
The factor 2.44 is twice the classic 1.22 Airy radius coefficient for a uniformly illuminated circular pupil in air; it is the textbook value used for quick diffraction blur estimates in photography, cinema lenses, and telescope or microscope sketches that share the same aperture geometry. Longer wavelengths or slower (larger) f-numbers enlarge the disk; shorter wavelengths or faster apertures shrink it. Green light near five hundred fifty nanometres is a common monochromatic stand-in for broadband daylight when you only need a first-order rule of thumb.
This capability evaluates only that closed-form Airy diameter and radius from wavelength and f-number. Both inputs must be finite and strictly positive; wavelength carries the length unit of the returned disk sizes while f-number is dimensionless.
Where photographers and makers use Airy disk numbers
Landscape and product shooters compare Airy diameter to photosite pitch to decide whether stopping from f/11 to f/16 still buys useful depth of field or only smears fine texture into diffraction mush. Macro and focus-stacking workflows need the same check because effective f-number rises as magnification grows, so the disk diameter you compute at the working N often exceeds the geometric depth-of-field gain you hoped for. Cinematographers and stills camera designers sketch diffraction-limited resolution at design wavelengths before locking pixel counts and optical low-pass choices.
Teachers and club mentors assign endless problems that ask for the Airy disk diameter or first-null radius from a green-light wavelength and a listed f-stop; a single trusted oracle that returns both lengths speeds grading and demo setup. If you later need hyperfocal distance, depth of field, crop factor, exposure value, or field of view, treat those as separate search intents and landings rather than overloading this Airy disk diameter page.
What you can do with it
Stop-down diffraction check
Compute Airy diameter at your working f-number and a design wavelength, then compare it to pixel pitch before you stop past f/11 on a high-resolution sensor.
Macro effective aperture tables
Build a table of Airy diameters across effective f-numbers as magnification rises so focus stacks stay diffraction-aware.
Homework and club demos
Return deterministic diameter and radius from textbook wavelength and f-stop so teachers, mentors, and auto-graders share one ground truth.
FAQ
What formula does this Airy disk diameter calculator use?
Disk lengths use the same unit as λ.
Which wavelength should photographers pick for daylight?
A common monochromatic stand-in is about 550 nm (green). Blue light gives a smaller disk; red light a larger one. For broadband scenes the green estimate is a practical first-order blur floor.
Does a larger f-number always mean more diffraction blur?
Yes for this model: d grows linearly with N. Stopping down from f/8 to f/16 doubles the Airy diameter at fixed wavelength, which is why very small apertures often look softer on modern high-megapixel sensors.
How big is the Airy disk at f/8 in green light?
At 550 nm and f/8 the disk measures 10736 nm across, that is 10.736 µm, with a radius of 5368 nm. Compare it with your sensor's pixel pitch to judge diffraction softness.
Why do photos look soft at f/16 or f/22?
Stopping down enlarges the Airy disk in proportion to the f-number. Once the disk spans clearly more than a pixel, fine texture and microcontrast soften even when focus and technique are perfect.
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-airy-disk \
-H "Authorization: Bearer $KIT_KEY" \
-H "Content-Type: application/json" \
-d '{"wavelength":550,"f_number":8}'const res = await fetch("https://api.kit.forhosting.com/hobby/photo-airy-disk", {
method: "POST",
headers: {
"Authorization": `Bearer ${process.env.KIT_KEY}`,
"Content-Type": "application/json"
},
body: JSON.stringify({
"wavelength": 550,
"f_number": 8
})
});
const { task_id } = await res.json();import os, requests
res = requests.post(
"https://api.kit.forhosting.com/hobby/photo-airy-disk",
headers={"Authorization": f"Bearer {os.environ['KIT_KEY']}"},
json={
"wavelength": 550,
"f_number": 8
},
)
task_id = res.json()["task_id"]<?php
$res = file_get_contents("https://api.kit.forhosting.com/hobby/photo-airy-disk", false, stream_context_create([
"http" => [
"method" => "POST",
"header" => "Authorization: Bearer " . getenv("KIT_KEY") . "\r\nContent-Type: application/json",
"content" => '{"wavelength":550,"f_number":8}',
],
]));
$task = json_decode($res, true);body := bytes.NewBufferString(`{"wavelength":550,"f_number":8}`)
req, _ := http.NewRequest("POST", "https://api.kit.forhosting.com/hobby/photo-airy-disk", body)
req.Header.Set("Authorization", "Bearer "+os.Getenv("KIT_KEY"))
req.Header.Set("Content-Type", "application/json")
res, _ := http.DefaultClient.Do(req)Example request
{
"wavelength": 550,
"f_number": 8
}Example response
{
"task_id": "tsk_a1b2c3d4e5f6a1b2c3d4e5f6",
"type": "hobby.photo_airy_disk",
"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
Why Airy disk diameter matters for diffraction blur
It does not integrate the full Bessel intensity envelope, does not model rectangular pupils or single-slit minima, does not convert f-number to numerical aperture, and does not fold in lens aberration, sensor demosaicing, anti-alias filters, or optical low-pass sampling. The pipeline is pure floating-point arithmetic with no network, no random seeds, and no wall-clock timestamps, so identical lambda and N always produce identical JSON.
What you send and what you get back
Both fields are required. Wire the free browser form for field decisions and homework, then call the identical contract from scripts when you need tables across a stop sequence. Send two numbers under the fields wavelength and f_number. wavelength is lambda in any length unit you prefer for the answer—many photographers enter nanometres such as five hundred fifty for green light, while scientific scripts may use metres—and f_number is the working relative aperture N equals f over D. Aliases such as lambda, wave_length, wl, or wavelength_nm for the wavelength, and fnumber, f_stop, fstop, N, fn, f_num, or aperture for the f-number are accepted so scripts written against common textbook or camera notation do not need a rename layer. Missing fields, non-numeric strings, NaN, Infinity, zero or negative wavelength, and zero or negative f-number fail with invalid_input and are not charged. On success the response echoes cleaned wavelength and f_number, returns airy_diameter equal to 2.44 times lambda times N, returns airy_radius equal to 1.22 times lambda times N, includes airy_factor 2.44, adds a short formula string d equals 2.44 lambda N, and a unit_note reminding you that disk lengths match the wavelength unit. Classic checks include five hundred fifty nanometres at f-number eight for a mid-stop landscape aperture, five hundred fifty at f-number sixteen where diffraction often rivals medium-format pixel pitch, a helium-neon-style six hundred thirty-three nanometres at f-number five point six for a longer monochromatic estimate, and a zero or negative f-number as the mandatory invalid_input path. Pricing for successful API calls is the published base of $0.002 per item; validation failures do not consume prepaid balance.
Where photographers and makers use Airy disk numbers
Because this capability is a pure parse engine, API pricing is the published base of $0.002 per successful item and failed validation does not consume balance.
Technical questions
What units should I use for wavelength?
Any consistent length unit (nanometres, metres, micrometres). The returned airy_diameter and airy_radius are in that same unit. Example: λ = 550 nm and N = 8 yields d in nanometres.
What does a failed request cost?
Validation failures (missing fields, non-finite numbers, λ ≤ 0, or N ≤ 0) return invalid_input and do not consume prepaid balance. Successful API calls are billed at $0.002 per item.