Terms of Service
About the service
Calculates the longest exposure before stars trail on a fixed tripod, using the NPF rule and the 500, 400 or 300 rule, and can read lens settings from a photo’s EXIF metadata. The service is provided as a free browser-based utility. These terms describe its intended use and limitations. Use the tool only if you agree to these terms.
Your files and responsibilities
You retain ownership of your files. Selecting a file does not grant the service a license to publish or reuse it. Only inspect or modify files you are entitled to use, and respect privacy, copyright and other applicable rights.
You are responsible for deciding what to share and for checking any result before relying on it. Keep backups of important originals. Do not use the tool for unlawful purposes or to interfere with the website or other users.
Calculation limitations
Results are estimates based on published rules of thumb and on the values you enter or that a photo’s metadata provides. Lens aberrations, focus, wind, atmospheric conditions, image processing and viewing size affect real results. EXIF values can be missing, rounded or written differently by some cameras; check them against your equipment. The results do not guarantee sharp stars and should not be used where accuracy is critical.
Local processing and privacy
Calculations and photo metadata reading run locally, as explained in the Privacy Policy. A selected photo is only read, never modified or uploaded.
Availability and warranties
The service is provided on an “as is” and “as available” basis, to the extent permitted by applicable law. No promise is made that it will always be available, error-free, compatible with every file or suitable for a particular purpose.
To the extent permitted by applicable law, liability for losses resulting from reliance on tool results, unsupported formats or incorrect metadata is excluded. Nothing in these terms excludes liability or limits consumer rights that cannot lawfully be excluded or limited.
NPF rule credit and links
The NPF rule was developed by Frédéric Michaud of the Société Astronomique du Havre (SAH). Its formulas are used here with credit to the author and the SAH, as requested on the SAH website. The calculator code and its EXIF reader are part of this tool and use no third-party libraries. Linked websites are outside this tool’s control.
Changes
Features and these terms may change. Updated terms apply to use after the update; they do not retrospectively change rights that arose earlier.