Camera sensors have vastly improved since the “old days” of the Rule of 500. This was an early attempt to estimate the longest shutter speed for a specific focal length lens. You divide the number 500 by the focal length, and that’s your max shutter speed.
For example 500 divided by a lens length of 50mm would be 10 seconds.
The chart below is based on the new Rule of 300.
| Lens Focal Length | Max Shutter Speed, seconds |
| 14 | 20 |
| 24 | 10 |
| 35 | 8 |
| 50 | 6 |
| 135 | 2 |
These are starting points and may need to be adjusted.
POTENTIAL HACK — If you face north or south, the sky’s motion seems slower than when facing east or west.