Star trail length
The opposite of freezing the stars: here you want trails. Enter your exposure and lens to see how long the streaks will be on the film.
Stars near the celestial equator trail longest; those near the pole (like Polaris) barely move and make tight circles. Reciprocity failure means very long exposures need even more time for density.
About this tool
The opposite of freezing the stars: here you want trails. Enter your exposure time, focal length and the declination of the stars, and this estimates how long the streaks will be on the negative and how much of the frame they cross.
How to use it
- Enter the focal length of your lens.
- Enter the exposure time in minutes.
- Enter the declination of the stars you are shooting.
- Read the trail length on film and the fraction of the frame it covers.
FAQ
Which stars trail the most?
Stars near the celestial equator move fastest and trail longest; stars near the pole barely move and form tight circles.
Do I need reciprocity correction too?
Yes, very long film exposures suffer reciprocity failure and need extra time for adequate density, so check the reciprocity tool.