How many subs do I need?
Pick a deep-sky target, your smart telescope and your sky. Get the total integration time and the number of sub-exposures for a quick look, a solid image, or a showpiece.
Calculator
What can I image tonight?
The tonight planner takes your location, date and scope, works out the dark hours and the Moon, and lists every target that is high enough for long enough, with whether the time it needs fits the night. Or browse month by month.
How it works
- Each target's brightness per square arcsecond, from its catalogue magnitude and size, sets how many photons land on each pixel.
- Your Bortle class sets the skyglow photons that land on the same pixel. The two compete; the sky usually wins from town.
- Your scope's aperture, pixel scale, read noise and sub length fill in the rest. The model solves for the time that reaches a target signal-to-noise. Full method and assumptions.
Popular targets
Telescopes
Not sure which? The buying guide picks by what you want to shoot and what you want to spend. Choosing between two? Compare any pair head to head: Seestar S50 vs DWARF 3, S50 Pro vs S50, and every other combination.
Guides
Questions people ask
What is a sub?
A sub, or sub-exposure, is one of the short frames a smart telescope takes and stacks. A Seestar takes 10-second subs by default; 360 subs make an hour of total integration. The stacked image improves with the square root of total time, so four times the subs gives twice the signal-to-noise.
Why does the sky matter more than the telescope?
Skyglow adds noise to every pixel. Going from a Bortle 8 city sky to a Bortle 4 rural one cuts the sky background roughly ten-fold, and for faint targets that shortens the time needed for the same result by a similar factor. No affordable telescope upgrade gets you that.
Are more subs always better?
Yes, with diminishing returns. Doubling total time improves signal-to-noise by about 41%. The figures here mark sensible stopping points for three quality levels; there is no hard ceiling, only your patience and the weather.