Terms of use

By using this site you agree to the following. It's short and in plain language.

Guidance only, not a guarantee

This calculator and the accompanying articles are provided for general photographic guidance. The 500 rule and NPF rule are estimates: the point at which star trailing becomes visible also depends on seeing conditions, lens quality, how much you crop, and how you view the final image. Treat the results as a sound starting point for your own test shots, not a promise of a particular outcome.

Accuracy

We work to keep the formulas and the built-in camera presets correct, but we make no warranty that every preset matches your exact camera or that a result suits your specific situation. You can always override the crop factor, sensor width and pixel count with values from your camera's specifications.

No liability

To the fullest extent permitted by law, we accept no liability for any loss or a missed shot arising from use of, or reliance on, this site or its calculations. You use the tool at your own risk.

Acceptable use

You may use the calculator freely for personal and professional photography. You may not attempt to disrupt the site, misrepresent it as your own, or use it unlawfully.

Changes

We may update these terms or the tool at any time. Continued use after a change means you accept the updated terms. Questions can go to the contact page.