Star Trail Calculator
Calculate the 500 rule exposure time for sharp stars or intentional star trails.
Avoid star trailing in astrophotography.
Maximum Exposure Time
The 500 Rule gives the maximum exposure time before stars start to trail:
Max Seconds = 500 / (Focal Length × Crop Factor)
For the more accurate NPF Rule:
Max Seconds = (35 × Aperture + 30 × Pixel Pitch) / Focal Length
Quick reference (full frame):
| Focal Length | Max Seconds |
|---|---|
| 14mm | 35 sec |
| 24mm | 21 sec |
| 35mm | 14 sec |
| 50mm | 10 sec |
| 85mm | 6 sec |
Tips for star photography:
- Use the widest aperture possible (f/1.4 to f/2.8)
- Use high ISO (1600–6400)
- Use a sturdy tripod and remote shutter release
- Focus on a bright star using live view magnification