What fits in your frame?

Field of view of any camera on any telescope or lens, from sensor size and focal length, using the exact arctan formula. With presets from maker specs.

Check whether a galaxy or nebula fits your sensor, with catalogue sizes and position angles, a star-chart preview and the focal length for a chosen fill.

Count mosaic panels for a nebula or galaxy from your sensor, focal length and overlap, with both camera orientations tried and a panel layout chart.

Arcseconds per pixel from pixel size and focal length (206.265 × µm ÷ mm), with binning, reducer factors and the telescope's resolution limit.

Pixels across the star FWHM for your camera, telescope and seeing, with under- and over-sampling verdicts, binning options and the published rules of thumb.

Effective focal length, focal ratio, image scale and field with a reducer or Barlow, from its nominal factor or from lens focal length and spacing.

Longest untracked exposure before stars trail, by the 500 rule and by Michaud's NPF rule (simplified and complete), with trail length in pixels.

Magnification, exit pupil and true field for any telescope and eyepiece, from apparent field or field stop, with Barlow and your own pupil size.

How many gigabytes a night of imaging produces: FITS frame size from resolution and bit depth, calibration frames, and 32-bit processing copies.

M31 spans about 3° × 1° in the SEDS catalogue. Which focal lengths fit it on APS-C, full-frame and 1-inch sensors, and how to rotate the camera.

SEDS lists M16 at 7′, but that is the star cluster. The nebula spans over 30′. Focal lengths for the whole Eagle and for the Pillars region.

IC 1805 and IC 1848 are 149′ apart in Cassiopeia. Their sizes differ by catalogue from 60′ to 150′; focal lengths and mosaics for the pair and each nebula.

M8 and M20 are 85.8′ apart in Sagittarius. Focal lengths that hold both, the catalogue sizes behind the numbers, and why latitude matters for this pair.

The three Leo Triplet galaxies span about 41′ × 24′ in catalogue outlines. Focal lengths that hold all three, and why catalogue sizes for M65 differ twofold.

M81 and M82 are 36.9′ apart, almost north–south. The focal lengths that fit both on APS-C, full-frame and square sensors, and why portrait helps.

NGC 7000 and IC 5070 are 83.5′ apart and together span about 181′ × 120′. Focal lengths for the pair, sizes from three catalogues, and mosaic options.

M42 measures 85′ × 60′ in the SEDS table and 66′ × 60′ in its text. Focal lengths for APS-C and full frame, M43 next door, and the bright Trapezium.

M101 is a face-on spiral of 22′ (SEDS) to 26.9′ (NGC 2000.0). Which focal lengths frame it, and why its best month differs from its midnight date.

The SEDS catalogue gives the Pleiades 110′. Which focal lengths frame the cluster on APS-C and full frame, and why the dust around it needs extra room.

The Rosette spans 100′ in the Sharpless catalogue, with the cluster NGC 2244 at its centre. Focal lengths for APS-C, full frame and square sensors.

M33 measures 73′ × 45′ in the SEDS catalogue but only 60′ × 36′ in SIMBAD. What that means for focal length, and when NGC 604 needs a longer lens.

The Cygnus Loop spans 230′ × 160′ in SIMBAD; its bright arcs NGC 6960 and NGC 6992 are 150′ apart. Focal lengths for the whole loop and for each arc.

M51 is only 11′ × 7′. How much focal length it needs on common sensors, why sampling sets the real limit, and where NGC 5195 sits.

Eighteen Canon, Nikon, Sony and Fujifilm bodies compared by sensor size and image size, with derived pixel pitch, crop factor and fields from 14 to 300 mm.

Twelve guide and small-sensor cameras at 120–600 mm: guide image scale against the main camera's, how much sky each sees, and when PHD2 suggests binning.

Seven IMX455 full-frame cameras: the 43.3 mm image circle the sensor needs, 122 MB per 16-bit FITS frame, and how the ZWO, QHY, Player One and ToupTek bodies differ.

Ten IMX533 cameras with an 11.31 mm square frame: why a square suits round targets, how orientation stops mattering, and where QHY's 3008 × 3028 figure differs.

Eleven cameras on Sony's IMX571: the same 3.76 µm pixels and near-identical fields, with differences in published cooling, back focus, full well and read noise.

Eight IMX585 cameras from ZWO, QHY, Player One and ToupTek: cooled and uncooled twins, two published pixel arrays, and 2.9 µm sampling at long focal lengths.

Player One's Poseidon, Ares, Zeus, Uranus, Saturn, Neptune, Mars, Ceres and Apollo cameras mapped to their Sony sensors, with cooled and uncooled twins compared.

QHYCCD's uncooled QHY5III line from 1.45 µm to 5.86 µm pixels: the focal ratio each pixel size needs, back focus with and without the adapter, and spec conflicts.

QHY's cooled cameras from the QHY183 to the QHY600, with sensor sizes computed from pixels × pitch, effective vs total pixel areas, and two discontinued models.

ToupTek's ATR, SkyEye, G3M and GP astronomy cameras decoded, with the resolutions ToupTek publishes for shared Sony sensors and where its own pages disagree.

ZWO's cooled ASI cameras grouped by sensor size, from the 1/1.2-inch ASI585MC Pro to the medium-format ASI461MM Pro, with computed fields and focal lengths.

ZWO's uncooled ASI cameras compared by pixel size and field: 1.45 µm to 5.86 µm pixels, image scale at long focal lengths, and the Mini guide cameras.

Askar APO triplets (700–1421 mm), self-flattened F refractors and f/3.6 N Newtonians: reducer focal lengths, a 28 mm image circle, and which sensors fit.

Askar SQA, FRA and PHQ astrographs: how the three lines differ, 0.7x–0.76x reducers with published focal lengths, and back focus measured from different threads.

Celestron RASA astrographs at f/2–f/2.2: published image circles vs sensor diagonals, camera body and back focus limits at prime focus, and how filters fit.

Celestron classic SCTs vs EdgeHD: the f/6.3 reducer vs 0.7x EdgeHD lenses, the 133.35/146.05 mm back focus, and why the manual's focal lengths differ.

Sharpstar f/2.8 HNT Newtonians, SCA260 and SCA310 Cassegrains and the Z4 refractor: image circles, obstruction, and which EDPH models are discontinued.

Esprit ED and EDX triplets from 400 to 1050 mm: which flattener came in the box, the 0.77x reducers for the 120 and 150, and the 70EDX's 490 vs 455 mm focal length.

Sky-Watcher ED doublets: discontinued Evostar ED vs current EDX, matched reducers, published reduced focal lengths and the 0.92x vs 1.0x flattener conflict.

Sky-Watcher PDS (f/5) and Quattro (f/4) imaging Newtonians: coma correctors that keep focal length, the Quattro 150P's 518 mm reducer and published secondary sizes.

Skymax Maksutovs (1300–2700 mm) and Classic/Flextube Dobsonians: exit pupil and magnification limits, planet image scale, and the Skymax 127 spec conflict.

Sixteen small refractors from 178 to 408 mm compared on APS-C field, image scale, focal ratio and image circle against APS-C and full-frame diagonals.

William Optics' Cat Petzval astrographs: the RedCat to Cat WIFD rename, MiniCat, Mighty-Cat and Ultra-Cat, image circles, and the 55 ± 3 mm spacing WO recommends.

William Optics doublets, triplets and Pleiades astrographs: flatteners published only as factors, computed focal lengths, per-scope back focus, FluoroStar 156.

What back focus is, why reducers and flatteners need an exact sensor distance, published values for real telescopes, and how to add up a spacer chain.

John Bortle's nine sky classes from 2001 with their naked-eye limiting magnitudes, where the published copies disagree, and how sky brightness enters imaging plans.

What bias, dark, flat and dark-flat frames record, why only (L − D) ÷ (F − O) removes vignetting and dust, what must match, and the disk space a library takes.

What drizzle integration does, why it needs dithered and undersampled frames, which camera and telescope pairs qualify, and what it costs in noise and disk space.

Magnification, exit pupil and true field formulas, why 50× per inch and the 7 mm pupil are conventions, and how the dark-adapted pupil shrinks with age.

The geometry behind 2·arctan(d/2f), how large the small-angle error gets, why imaging area is pixels × pitch, and why crop factor is a framing convention.

How ADC bit depth, full well and system gain in e-/ADU decide where a CMOS astro camera saturates, what unity gain is, and how binning affects read noise.

How guide-camera image scale compares with your imaging scale, what PHD2's documentation says about arcseconds and RMS, sub-pixel centroids, and the 1:4 rule.

What arcseconds per pixel mean physically, how 206.265 falls out of s = Fθ and the radian, and how pixel size, focal length, binning and Bayer filters change it.

The CCD equation behind exposure planning: why S/N grows with the square root of total time, when read noise makes sub length matter, and what it costs in storage.

How a Bayer color filter array splits the pixels, what that does to the image scale of each color, and what a mono camera with filters changes.

Emission-line wavelengths from NIST, why steep light cones shift filter passbands to the blue, and which f/2–f/4 telescopes in our data are fast enough to matter.

Where the 500 rule came from, how Frédéric Michaud's NPF rule adds f-number, pixel pitch and declination, and how the two compare on real camera bodies.

Thin-lens formulas for reducers (R = 1 − d/f) and Barlows (M = 1 + d/|f|), why spacing changes the factor, designed back focus, and what a faster f-ratio buys.

Dawes' 4.56″ rule and the Rayleigh criterion 1.22 λ/D, worked for real apertures, and why atmospheric seeing sets the limit for long exposures.

Why imagers put two to three pixels across a star's FWHM, how AAVSO, Diffraction Limited, Stan Moore, Atik and a PASA paper disagree, and what seeing to expect.