Compute a maximum untracked shutter for pinpoint stars with the NPF rule and compare it against the classic 500 rule.
Frequently asked questions
What is the NPF rule?
NPF uses focal length, aperture, and pixel pitch to estimate the longest untracked exposure before stars elongate.
Why not only the 500 rule?
The 500 rule ignores pixel size. Dense sensors trail sooner; NPF is usually stricter and more realistic.