Exposure time is the heartbeat of your astrophotography session. Too short, and faint stars vanish; too long, and noise or star trails spoil your shot.
Here’s what math tells us:
- Doubling exposure time roughly doubles the light collected.
- But noise and star trailing increase with longer exposures.
- Using multiple shorter exposures and stacking them improves signal-to-noise ratio (SNR) by about the square root of the number of frames.
For example, stacking 16 exposures improves SNR fourfold compared to a single shot.
Tip: Calculate your maximum exposure based on your lens focal length and mount stability, then plan stacking accordingly.