How this is calculated
Signal-to-noise ratio (SNR) for one sub-exposure follows the CCD equation: SNR = S·t ÷ √(S·t + B·t + D·t + R²), where S is target signal rate, B is sky background, D is dark current, R is read noise, and t is exposure time, all in electrons. Each value is per pixel.
Stacking N identical sub-exposures improves SNR by the square root of N. The tool reports the stacked SNR and the number of sub-exposures needed to reach your target.
The sky background and dark current values should come from your camera's specifications and your imaging software's measurements. This tool does not convert light pollution scales (such as the Bortle scale) into sky background, because published conversions vary. Read the sky background from your own images.
Frequently asked questions
What is SNR in astrophotography?
Signal-to-noise ratio compares the target's signal with the noise in an image. Higher values give cleaner results.
How does stacking help?
Stacking identical sub-exposures improves SNR by the square root of the number of frames.
Where do I find sky background and read noise?
Use your camera's specifications and the measurements shown in your imaging software.
Keep reading on Astralis & Aperture
- Signal to noise in deep-sky imagingRelated article on this site
- Narrowband filters and emission linesRelated article on this site