Photography calculators

Viewpoint includes a set of field calculators — depth of field, hyperfocal distance, long exposure, the astro tools, and a few framing helpers. They’re all on-device and work offline: no signal needed at the trailhead.

Each calculator has an (i) button in the app with a short version of what’s below. This page is the long form — what each tool is for, how it’s worked out, and when to reach for it.

Try them free, right now, in your browser — the same engine the app runs, no install and no sign-up. Each is a taste of what the app does in the field, where you also get the depth-of-field overlay, the sun/moon/Milky-Way planner, GPS auto-stamping and full offline use.

New to photography? Terms like aperture, f-number, stop, focal length, and crop factor are all explained in plain language in Photography basics — skim it once and everything below clicks into place. Each section here keeps the wording as plain as it can, then points you there for the deeper definition.

Note: The in-app (i) explainer and this page are kept in step: every calculator here has a section in the app, and every calculator in the app has a section here.

Depth of field

Depth of field is how much of your scene is sharp, front to back — the zone around whatever you focused on that still looks crisp, with everything nearer or farther melting into blur. A portrait with a creamy, blurred background has a shallow depth of field; a landscape sharp from the flowers at your feet to the peak on the horizon has a deep one. Knowing which you’ll get — before you’re standing there in the field — is the difference between the shot you wanted and the one you settled for.

Three things set it, and it helps to feel how each one pulls:

• Aperture (the f-number). A wider opening (smaller number, like f/2.8) puts less in focus; a smaller opening (bigger number, like f/11) puts more in focus. This is the lever most people reach for first.
• Focal length. A longer lens (a 600 mm telephoto) gives less in focus; a shorter lens (a 24 mm wide-angle) gives more.
• How far you are from your subject. The closer you stand, the less is in focus; step back and the sharp zone deepens. (Sensor size matters too — smaller sensors give more depth of field, which is why phone photos rarely blur the background.)

The part that surprises people: a longer, “faster” lens can leave less in focus, not more. Say a bird is sitting 30 m away. A 600 mm at f/2.8 — the expensive, fast choice — gives you a razor-thin sharp zone: get the eye pin-sharp and the far wing is already soft. A humbler 400 mm at f/4, from the same spot, keeps noticeably more of the bird sharp, because the shorter focal length and the narrower aperture both work in your favour. “Longer and faster” is the right call when you want to isolate a subject against melted-away surroundings — but when you want the whole subject sharp, it can be exactly the wrong lens to bring. That trade is the reason to check before you pack the bag.

So the calculator answers two real questions: “with the lens I have, how much will be in focus at this distance?” and “which lens and aperture should I bring for the shot I’m planning?” A still subject you can stop down and hold sharp; an action subject often pins you near wide-open, and the depth of field is whatever it is — better to know going in.

Compare mode answers that second question directly: set your subject distance, put two lens-and-aperture setups side by side, and see which keeps more of the scene sharp — the “you brought the wrong lens” conversation, settled before you leave the house.

Technique. When no single aperture can hold a close foreground and the horizon both sharp, focus-stack — a few frames at different focus distances, blended in post — instead of stopping so far down that diffraction softens everything (past about f/11 on full frame the lens loses more sharpness to diffraction than it gains in depth).

Gear. Tripod (the frames must align for the blend).

Hyperfocal

The single focus distance that keeps everything from half that distance out to infinity acceptably sharp. It’s the classic landscape move for front-to-back sharpness: focus at the hyperfocal distance and the whole scene from the mid-foreground to the horizon falls within the depth of field. H = f² / (N · c) + f, where f is the focal length, N the f-number, and c the sensor’s circle of confusion. Shorter lenses and smaller apertures pull the hyperfocal distance nearer, so more of the scene is sharp — which is why a wide angle at f/11 holds everything from a metre out to the horizon.

Technique. Focus a third into the scene, not the horizon — focusing at infinity wastes half your depth of field behind the subject. Stop down a couple of stops for the result.

Gear. Tripod for the slower shutter.

Long exposure

Your new shutter speed after screwing on an ND filter. Each stop of ND halves the light, so it doubles the exposure time: t = base × 2^stops. Dial in your un-filtered base shutter and the filter strength, and you get the timed exposure to set on the camera (or on a remote for anything past 30 s). Handy for smoothing water, blurring cloud, or dropping a daylight exposure into multi-second territory. On a digital sensor a stop is a stop however long the frame — the real limits on minutes-long exposures are sensor heat and battery, not the math.

Technique. Compose, focus, and meter without the filter first — a 10-stop is far too dark to meter or focus through, and that un-filtered shutter is the base the calculator multiplies. Then fit the filter, switch to manual focus so it can’t hunt, and trip the shutter on a remote or the 2-second timer. No ND? Take a burst of normal exposures and median-stack them in post — water and cloud smooth out, much like one long frame, while the static scene stays sharp.

Gear. Tripod, remote or 2-second timer, ND filter (or the burst-and-stack workaround).

Spot stars

The longest exposure before stars trail — before the Earth’s rotation (about 15°/hour) turns pinpoints into streaks. The 500 rule is the quick estimate: 500 / (focal × crop). The NPF rule is more accurate because it accounts for your aperture and how tightly your sensor samples detail: NPF = (35·N + 30·p) / f, where N is the aperture, p the pixel pitch in microns, and f the focal length. High-resolution sensors and fast lenses show trailing sooner, so NPF usually gives a shorter time than the 500 rule. Use the shorter (safer) of the two, then raise ISO to get the exposure — and recover the cleanliness by stacking, below.

Technique. Keep the exact same framing for every frame, then stack several (median or average) to beat down the high-ISO noise — noise is random and partly cancels, so a handful of frames gives a clean Milky Way without trailing. Don’t nudge the camera between frames or they won’t align.

Gear. Tripod, a fast wide lens.

Star trails

The opposite goal: let the stars streak. This tells you how far the sky rotates over your exposure — the angle your trails sweep. The sky turns about 15°/hour (one full turn per sidereal day), so rotation = 15.04°/h × hours. Duration and rotation are coupled both ways: set the time you have and read the angle you’ll get, or set the angle you want and read the exposure time it needs. Pick the hemisphere so the diagram shows the right pole — trails circle Polaris in the north; the southern sky has no bright pole star. An individual star’s arc scales with how far it sits from the pole (star arc = rotation × cos(declination)): a star near the celestial equator traces the full rotation, one near the pole circles tightly and barely moves — which is why trails curve around the pole.

Technique. Rather than one 3–6 h exposure (which blows out the sky, and one bump ruins everything), shoot a sequence of 30 s frames and stack them in post. The timelapse calculator gives the frame count for your total time.

Gear. Sturdy tripod that doesn’t shift between frames, intervalometer.

Timelapse

Turns a shoot plan into numbers: the frame count, the final clip length, and a rough storage estimate, from your interval, the event’s duration, and the playback frame rate. frames = event ÷ interval, clip = frames ÷ fps. Use it the other way too — work back from the clip length you want to the interval you should shoot at. Match the interval to how fast the scene moves: 1–2 s for fast clouds or a busy street, 5–10 s for a sunset, 20–30 s+ for stars (those same frames also stack into a star-trail image).

Technique. Shoot in manual exposure, and lock white balance too, so brightness and colour don’t flicker frame to frame. For a sunset-to-night “holy grail” timelapse the light changes by many stops — ramp the exposure gradually (a few clicks of ISO or shutter spread over many frames) rather than letting auto-exposure pump.

Gear. Tripod, intervalometer.

Exposure

The exposure value (EV) of an aperture / shutter / ISO combination — a single number for “how much light”, which makes it easy to compare two settings or judge a scene. EV = log₂(N² / t) + log₂(ISO / 100), where N is the aperture and t the shutter in seconds. Two settings with the same EV give the same brightness, so you can trade aperture for shutter for ISO with confidence. As a feel for the scale at ISO 100: bright sun sits near EV 15, an overcast day near EV 12, a moonlit landscape down around EV −3.

Technique. Expose to the right — push the histogram as bright as you can without clipping the highlights — for the cleanest shadows, then pull it back in post. Watch the highlight blinkies and the per-channel (RGB) histogram, not just the overall one: a single channel (often red in a sunset) can blow out while the combined histogram still looks safe. Shoot RAW for the most recovery room.

Panorama

How many frames you need to cover a sweep, so the set stitches cleanly. It works out the per-frame field of view from your focal length and sensor, then divides the total sweep by the new coverage each frame adds after overlap: frames = ⌈sweep ÷ (frameFOV × (1 − overlap))⌉. Leave 20–30% overlap so the stitcher has something to match on, and shoot a touch wider than you think — you’ll crop the ragged edges later.

Technique. Lock exposure and white balance to manual (and manual focus too) so the sky doesn’t step in brightness or colour between frames. Keep the horizon level — a tilted pano loses a lot to the crop. When the foreground is close to the camera, rotate around the lens’s nodal point so near and far don’t shift against each other (parallax), or the stitcher can’t register them.

Gear. Tripod, a level — ideally a nodal-point pano head.

Subject distance

How far to stand so a subject of a known real height fills the frame. From the lens projection, distance = focal × height ÷ sensor height. Tell it the subject’s real size, your focal length and sensor, and it gives the distance at which the subject fills the frame height — useful for wildlife (how far back for a deer to fill the frame), portraits with a long lens, or planning a shot before you’re on location. It’s the tightest possible framing, so leave a little room: stand a touch farther back than the number if you want headroom around the subject.

Focal match

The focal length on one camera that frames the same view as a focal length on another — for when you switch between bodies with different sensors. f₂ = f₁ × crop(source) ÷ crop(target). For example, 50 mm on full frame matches about 33 mm on APS-C. Use it to pack the right lens, or to reproduce a framing you liked on a different body.

Related

• Photography basics — plain-language glossary of every term used above.
• Getting started
• AR Celestial Scout
• Sun, Moon & Milky Way