๐ท Astrophotography Exposure Calculator
Calculate optimal exposure settings for deep sky astrophotography. Determine the best ISO, exposure time, and number of frames for maximum image quality.
Exposure Guidelines
The Exposure Triangle
Astrophotography involves balancing three key parameters to capture optimal images:
๐ท ISO Sensitivity
Higher ISO captures more light but increases noise. Modern cameras handle ISO 1600-6400 well.
โฑ๏ธ Exposure Time
Longer exposures gather more light but risk star trailing. Use the 500 rule as a starting point.
๐ข Number of Frames
More frames reduce noise when stacked. Total exposure time is more important than individual frame length.
The 500 Rule & NPF Rule
These rules help calculate maximum exposure time before star trailing occurs:
๐ 500 Rule (Simple)
Max Exposure = 500 รท Focal Length (mm)Example: 500 รท 50mm = 10 seconds maximum
๐ฏ NPF Rule (Precise)
More accurate formula considering pixel size and declination:
t = (35 ร p + 30 ร pยฒ) รท (f ร cos ฮด)๐ฏ Astrophotography Target Recommendations
| Target Type | Focal Length | Typical Exposure | ISO Range | Notes |
|---|---|---|---|---|
| ๐ Milky Way | 14-35mm | 15-30s | 1600-6400 | Wide field, avoid moon |
| โ๏ธ Large Nebulae | 50-200mm | 2-10min | 800-3200 | Use narrowband filters |
| ๐ Galaxies | 200-600mm | 5-20min | 800-1600 | Need dark skies |
| ๐ช Planets | 1000mm+ | 1/60-1/4s | 100-800 | Video stacking |
| ๐ Moon | 400mm+ | 1/500-1/60s | 100-400 | Avoid overexposure |
Signal-to-Noise Ratio
SNR improves with total exposure time. Staking many shorter exposures often works better than fewer long ones.
Light Pollution
In light-polluted areas, use shorter exposures and more frames. Consider narrowband filters for nebulae.
Camera Settings
Shoot in RAW format, turn off noise reduction, and use manual focus with live view magnification.