Starlapse vs AstroPile

Photograph the night sky properly, on a phone that was never meant to. Starlapse locks the camera and keeps it locked. ISO, shutter, focus, white balance — set them once and they stay there for the whole session. No creeping exposure, no autofocus hunting in the dark and landing on nothing, no auto white balance turning the sky orange under a streetlight. Then it does the thing the hardware cannot do alone. An iPhone sensor caps a single frame at about one second, so exposures longer than that are built by stacking hundreds of frames. That is not a workaround — it is better. Noise falls as the square root of the frame count, and the same night's light can be developed as pinpoint stars or as star trails afterwards, because nothing is thrown away. WHAT IT DOES • Manual camera that holds — ISO, frame exposure, focus, white balance, lens choice • Autofocus on starlight — steps the lens and measures star size, the way observatories focus • Self-timer, 3 or 10 seconds, so touching the phone does not shake the first frames • Stacking from 10 seconds to a full hour of collected light • Pinpoint stars — frames aligned on the stars themselves, so they stay points • Star trails — the sky's rotation drawn as arcs, ground kept sharp • Night time-lapse where every frame of the video is its own stack • Meteor detector — watches the sky and saves a short clip around anything that crosses it • Aiming overlay showing planets, bright stars and the Moon — tap any of them for its name, constellation and brightness WHERE TO POINT Most apps show you where a shower's radiant is. Starlapse tells you where to aim, which is not the same place: meteors streak away from the radiant, so the longest trails appear 40° off to the side. It works that out from your location and the time, keeps you clear of the Moon, and picks a height a tripod can actually hold. FOCUS, WHICH IS THE HARD PART Autofocus cannot see a night sky — there is no contrast to hunt on — and the infinity mark is not exactly infinity: it is a mechanical end stop, and the sharp point sits slightly inside it, at a place that differs between lenses and drifts as the phone cools. Starlapse steps the lens across its range, measures how large the stars come out at each position, and settles on the smallest. It takes about a minute. DEVELOP AFTERWARDS The stack is kept as accumulated light, not as a finished picture. When the exposure ends you can move the curve — stretch, black point, exposure, saturation — and it re-develops from the original data. Same latitude a RAW file gives you, which matters when you are judging a night sky on a phone screen in the dark. The curve is asinh, the one professional astronomical imaging uses. It lifts the faint Milky Way out of the noise while bright stars keep their cores and their colour instead of clipping to white discs. HONEST LIMITS • Aperture is fixed on iPhone. It is a property of the lens, not a setting. The app shows the f-number and what each lens gives up, and lets you choose — that is all any app can do here. • A single frame is about one second. Everything longer is stacked, and the interface always shows the arithmetic: "10 min of light = 600 × 1.00s". • Capture cannot run in the background. iOS stops the camera when an app leaves the screen. Starlapse keeps the screen on and dims it instead. • You need a tripod. An hour of stacking on a handheld phone is an hour of nothing. PRIVACY No account, no server of ours. Location and motion are used on the device to work out where to aim, and never leave it. Two things leave the phone: the optional purchase below, to Apple, and a usage counter you can switch off. The source is public: github.com/fortunto2/starlapse. STARLAPSE PRO Everything above is free and stays free. Pro is the sky's events, bought once: tonight's showers with their rates, the aim target 40° off the radiant and clear of the Moon, and peak nights. Comets, eclipses and dark frames join Pro at no further cost.

One phone photo of the night sky is mostly noise. Stack a dozen shots of the same scene and the noise averages away while the faint detail stays — that is what astrophotographers call stacking. AstroPile does it on your phone, entirely offline: no network permission, and no photo is ever uploaded. WHAT MAKES IT DIFFERENT IS THAT IT TELLS YOU WHAT HAPPENED. Most stackers hand you one picture. If it came out smeared, you have no idea which frame ruined it. AstroPile gives every frame a report card: • how many stars were detected • how many matched the reference frame • the alignment residual, in pixels • a 0–100 quality score Frames that could not be aligned say why — too few stars, too bright, no matching star pattern, residual too large, different pixel size — plus one line on what to change. Untick it and stack again. HOW IT WORKS 1. Pick two or more shots of the same scene 2. Choose the reference frame (the first one by default) 3. Start stacking — you can stop at any point 4. Drag black point, brightness and saturation; the preview updates live 5. Save to Photos or Share — the export is full resolution HOW IT ALIGNS Not by corner detection: stars look identical to each other, so feature matching does not work on a star field. AstroPile matches asterisms — the shape of the triangle each star forms with its neighbours — then uses RANSAC to throw out the false pairs and solves for shift, rotation and scale. This is the standard approach for registering star fields with no WCS information. DETAILS THAT MATTER • Reads EXIF on import and flags frames shot with different exposure settings than the rest • Frames with a different pixel size are marked in red instead of quietly ruining the stack • Combines in horizontal bands, so even a few dozen full-resolution frames will not exhaust memory • Scratch files are deleted when the run ends, and swept again on the next launch FREE Up to 6 frames per stack, mean stacking, full-resolution export, and the full per-frame alignment report. No ads, no watermark, no account. ASTROPILE PRO (a one-time purchase, not a subscription) • Up to 32 frames per stack • Median stacking — aircraft, satellite trails and hot pixels drop out on their own • Remembers your stacking mode and working resolution PRIVACY The app requests no network permission and contains no analytics or advertising SDK. Photos are read and processed on this device only; the finished picture leaves the app only when you save or share it. CREDITS Star-field registration follows astroalign (MIT, © 2016 Martin Beroiz), frame stacking follows OpenSkyStacker (MIT, © 2017 Benjamin Schubert), and the star-sharpness check follows the published design of astra_lite (MIT, © 2023 Denis Artyomov). This app is an independent Dart implementation and copies none of their code.