What is the maximum shutter speed before star trailing at 14mm on full frame?

At 14mm on a 24-megapixel full-frame camera pointed near the celestial equator — where stars trail fastest — the NPF rule puts the threshold at roughly 20 seconds; the simpler 500 rule allows roughly 36 seconds. Anything past whichever threshold you're targeting, a star that should render as a clean point starts stretching into a visible short streak.

This Is a Threshold, Not a Hard Wall

Trailing doesn't switch on abruptly at exactly one number — it's a continuous, gradual effect, and both rules mark the point where trailing becomes noticeable at their respective standards of scrutiny (full-resolution pixel-level for the NPF rule, normal viewing size for the 500 rule), not a hard physical cutoff. A shot at 22 seconds instead of the NPF rule's 20 won't look dramatically different from one at 18 seconds; it's a gradient you're choosing a point along, informed by how the two rules bracket it.

When Exceeding This Threshold Is the Whole Point

Star trail photography deliberately blows past this limit — a single multi-minute exposure, or dozens of stacked shorter exposures, intentionally renders stars as visible arcs tracing the sky's rotation around the celestial pole, the opposite goal from a pinpoint Milky Way shot. Knowing this threshold matters for that genre too, just in reverse: it tells you exactly how short an exposure would need to be to avoid the trailing effect you're actually trying to create.

Check this threshold for your own camera, lens and target declination in the Astro 500/NPF Rule Calculator.