The 500 Rule Tool

Capture the cosmos. Calculate the maximum shutter speed you can use before the rotation of the Earth causes stars to appear as "trails" rather than sharp points.

The zoom level of your lens.
Recommended Max Exposure
20s

Perfect for Milky Way photography.

Equivalent Focal
24mm
ISO Range
1600 - 6400

Mastering the Night Sky

I genuinely believe that astrophotography is one of the most rewarding forms of photography, but it's a battle against physics. Because the Earth is constantly rotating, stars move across the sensor of your camera. If your shutter is open for too long, they will appear as elongated blurs instead of pinpricks of light.

What is the 500 Rule? It's a simple mathematical formula used by photographers to find the threshold where star trailing becomes noticeable. The formula is: **Exposure Time = 500 / (Focal Length × Crop Factor)**.

Astrophotography Tips:

  • Manual Focus: Autofocus will not work on stars. Use "Live View" to zoom in on a bright star or a distant light and manually focus until the point of light is as small as possible.
  • Wide Open: Use the widest aperture your lens allows (lowest f-number, like f/1.8 or f/2.8) to let in as much light as possible.
  • Tripod: A sturdy tripod is non-negotiable. Even the slightest vibration from your finger pressing the button can ruin a shot—use a 2-second timer or a remote shutter.