The 500 rule isย used to calculate the maximum exposure time you can shoot before you start to see star trails.
to determine the optimal length of exposure for a camera with a Full Frame sensor, you take 500 and divide it by the effective focal length of the lens (Exposure time = 500/focal length).
For a 28 mm lens use the following equation seen below
500 divided by 28 = 17 – You would be able to expose your image for 17ย seconds before starting to see star trails.
