Field calculators
Seven answers,
one setup.
Pick your camera once and every calculator on the page updates. No accounts, no uploads, no cookie banner. If you already know your pixel pitch you can skip the camera list entirely.
Your setup
Set this once.
35.6 × 23.8 mm · 6000 × 4000 px · crop 1.01×
Pixel pitch here is derived from published sensor dimensions and pixel counts, so it can differ by a hundredth of a micron from a manufacturer figure. If you are chasing the last fraction of a second, check your manual.
Untracked shutter
How long before stars trail.
The old 500 rule ignores your sensor entirely, which is why it looks fine on a 12-megapixel camera and produces obvious trailing on a 60-megapixel one. NPF accounts for aperture and pixel pitch. Use the strict column if you print large or pixel-peep. Formula reference: PetaPixel / Frédéric Michaud, SAF ↗
Framing
Will it fit?
Very wide. The target becomes a detail in a landscape or a star field rather than the subject.
Sampling
Arcseconds per pixel.
Heavily undersampled. Stars will look blocky and small targets will not resolve. Consider drizzle if you dither well.
Calculated as 206.265 × pixel pitch in microns ÷ focal length in millimetres. Typical amateur seeing sits around 2 to 4 arcseconds, so sampling much finer than that mostly records atmosphere.
Integration
What the stack buys.
Signal to noise improves with the square root of frame count, so going from 60 frames to 120 buys you about 1.4 times better noise, not twice. Doubling perceived quality usually means roughly quadrupling the hours. This is the single most useful thing to internalise before buying anything.
Condensation
Dew margin.
Glass radiates heat to the sky and drops below air temperature, so dew forms on your front element before the margin actually reaches zero. Start gentle heat while you still have three degrees in hand, not after the frames go soft.
Star trails
Arc length.
The sky turns 15.04 degrees an hour. A recognisable arc needs at least 15 to 20 degrees, so plan an hour minimum. Shoot a continuous sequence of short frames rather than one enormous exposure: it protects against a plane, a car, or a satellite ruining the entire night.
Foreground focus
Hyperfocal distance.
Focused at the hyperfocal distance, everything from about half that distance to infinity holds acceptable sharpness. In practice, nail focus on a bright star first and check the corners.
Circle of confusion here is the sensor diagonal divided by 1500, which is stricter than the traditional 1/1730 print standard and closer to what a modern screen reveals.