Know what you caught last night, before you stack a single frame.
Clear nights are rare - every hour counts. Point AstroLoupe at your capture folder, step through the frames with the arrow keys, and see whether focus held, whether the corner stars are round, and whether the tilt you've been chasing is actually there.
Native to Apple Silicon, built for serious deep-sky astrophotographers - works alongside N.I.N.A., ASIAIR, or whatever you already capture with
Every imager knows the ritual: pour the coffee, open the capture folder, and quietly hope that the night went perfectly. AstroLoupe is a fast viewer joined to the measurements that answer the questions you'd otherwise ask by eye.
GPU-rendered with a PixInsight-style auto-stretch, so faint detail is visible the moment a frame opens. After Grade Frames or Trend has measured the folder, twilight and other unusually bright (or dark) subs get an orange HUD warning when their sky background is ≥2σ from the session median for that target and filter - with moon geometry cited when coordinates are known, and moonlit broadband frames near a bright moon left unflagged.
One-shot-colour frames are demosaiced and colour-balanced on the fly - mono frames stay neutral.
Opens FITS (incl. RGB cubes, 32-bit float, and fpack Rice/GZIP .fits.fz), XISF (incl. zlib/LZ4/zstd), TIFF/PNG and camera RAW (CR3/NEF/ARW/DNG), reading EXIF metadata from RAW just like a FITS header.
The GPU renders every frame; batch analysis fans out across all CPU cores. Ninety 60-megapixel subs are measured by the whole machine, not one core.
True field of view, orientation and pixel scale, matched against a bundled all-sky star catalogue. Seeded from the header, or fully blind across every core.
Scroll, pinch, click-to-zoom, drag a marquee, or snap to 1:1. Grab-and-drag to pan.
A 3×3 grid of magnified crops - centre, edges and corners - to compare star shape across the field at a glance.
Median HFD per region, drawn as a distorted quad that points at the tilt - with a tilt percentage.
Per-region eccentricity as an intuitive axis ratio, with direction and a traffic-light colour - the tell that separates corner coma from tracking error.
Do elongated stars all point the same way? A dedicated toolbar tool draws each star's axis (green when it agrees), a consensus arrow for the tracking direction, and a plain-language mount-vs-optics verdict - not just a number.
A dense field of elongation vectors where colour and length signal quality: tiny green is round and flat, growing red is trouble. Tilt or curvature draws a coherent pattern to the corners.
A gentle heatmap of star size across the whole field, drawn from FWHM - which, unlike HFD, doesn't grow with brightness, so it isolates real focus, curvature and tilt. Average it across a session and sensor tilt appears as a clean gradient you can measure.
Measure every light in the folder and average them for a far more reliable tilt estimate, with a significance figure and a plain High/Medium/Low verdict.
Averages drift-subtracted corner elongation across a session for a stable back-focus verdict: radial means too close, tangential too far.
Measure orientation-consensus trailing on every light frame and roll up median score, consensus position angle, and tracking-vs-optical frame counts into one plain-language session verdict.
Every metric in one sortable table (opens by capture time), with a keeper recommendation when analysis finishes: classic FWHM pruning or SNR contribution for quality-weighted stacking. On a uniform good night it tells you to keep all instead of peeling another layer. Drag the orange cut line, see predicted stack-SNR cost and integration time removed, then send discards to the Trash.
One button rolls up tilt, back-focus, guiding stability, dither/drizzle, sharpness, focus trend, focus-temperature compensation, sky transparency (with cloud-episode detection), moon conditions across the batch, site Bortle context and the keeper plan into a single graded report with a plain-language headline.
One tap switches every figure - including the per-star labels in the viewer - between HFD in pixels and FWHM in arcseconds, computed from the header's focal length and pixel size.
Plot HFD, FWHM, eccentricity, SNR, star count, trailing score or extended-structure Signal against clock time across the folder: focus drift, mount trailing, a passing cloud or a bad run of guiding at a glance. Twilight shading and moonrise/set markers when site coordinates are present.
Sky background, robust noise and median star SNR for every frame - in the clipping tool and the grading table.
Frame HUD shows moon illumination, altitude and separation from the target when coordinates are known. The Session Report rolls moon conditions up across the batch; Trend marks moonrise and moonset. Site Bortle context from the bundled Falchi atlas when SITELAT/SITELONG are in the header.
Browse the full, ordered header - keyword, value and comment - with a live filter.
Unstretched per-channel histogram focused on the tails, with the actual highlight-saturation fraction shown to two decimal places (0.1% tolerance for star cores). Fully-clipped regions are circled on the image.
Filter by object, filter, camera or filename - and the browser shows only lights by default, keeping calibration frames and masters out of the way.
Watches the capture folder and updates as new subs land, asking first before scanning very large folders.
A deep-sky image passes through three pieces of software on its way to being a picture. AstroLoupe gives you a proper look at the subs between capture and stack. Its ultra-fast design and GPU architecture outperforms at this task.
Your rig runs the session and fills a folder with subs while you sleep.
Step through the night, measure what happened, and grade what goes forward. Soft subs stop here - and so do mechanical faults, caught before the next clear night rather than after it.
Calibrate, register and integrate the keepers. Fewer soft subs in, sharper master out.
Stretch, gradients, colour - the part everyone actually sees.
Nothing to migrate and nothing to replace: AstroLoupe reads the folder your capture software writes, and hands the survivors straight to whatever you stack with.
“I was frustrated with slow software. Looking at my subs meant loading them into software built to stack them - a step that took forever and was never quite answering the questions I was asking. I craved a low-latency diagnostic tool like AstroLoupe. If this tool saves you one night of stacking soft frames, or finally settles whether that corner is tilt or curvature, it has done its job.
Clear skies.”
Michael Wells - author of AstroLoupe