The 500 Rule
What is the 500 rule? The wider your lens, the longer your shutter speed can be before the stars start to move.
The equation divides 500 by the focal length of your lens. For example, with a 50mm focal length, you’ll have 10 seconds before the stars move (500 divided by 50 equals 10). With a 24mm focal length, you’ll have 40 seconds before the stars move.
Basically, the shutter speed limit changes based on your focal length.
Here is a rough starting point to help practice:
- On a zoom lens: ISO = 6400, aperture = f/2.8, shutter speed = 15 seconds
- On a prime lens: ISO = 3200, aperture = f/1.4, shutter speed = 8 seconds