How long to image the Cave Nebula with the ZWO Seestar S30 Pro
From a Bortle 6 suburban sky, the ZWO Seestar S30 Pro needs about 4 h 51 min (1,747 subs of 10 s with the built-in dual-band (LP filter) filter) for a solid image of the Cave Nebula. A quick look takes 1 h 13 min; a showpiece 19 h. Under a Bortle 3 rural sky the solid figure drops to 3 h 22 min. At Bortle 6 the limit is a mix of skyglow and read noise. In this scope's field it fills 37% of the frame’s short side.
| Sky | Quick lookTarget obvious, still noisy | SolidClean enough to share | ShowpieceSmooth faint detail, print-worthy |
|---|---|---|---|
| Bortle 1Excellent dark site | 48 min291 subs | 3 h 14 min1,162 subs | 13 h4,646 subs |
| Bortle 2Typical dark site | 49 min295 subs | 3 h 17 min1,180 subs | 13 h4,718 subs |
| Bortle 3Rural | 51 min304 subs | 3 h 22 min1,214 subs | 13 h4,854 subs |
| Bortle 4Rural / suburban transition | 54 min324 subs | 3 h 36 min1,296 subs | 14 h5,183 subs |
| Bortle 5Suburban | 59 min357 subs | 3 h 58 min1,427 subs | 16 h5,705 subs |
| Bortle 6Bright suburban | 1 h 13 min437 subs | 4 h 51 min1,747 subs | 19 h6,986 subs |
| Bortle 7Suburban / urban transition | 1 h 38 min590 subs | 6 h 33 min2,357 subs | 26 h9,426 subs |
| Bortle 8City | 2 h 18 min826 subs | 9 h 11 min3,304 subs | 37 h13,214 subs |
| Bortle 9Inner city | 3 h 42 min1,331 subs | 15 h5,324 subs | 59 h21,295 subs |
Power and kit for this session
Allowing for slewing, focusing and rejected subs, that is about 6 h 18 min of run time. The Seestar S30 Pro’s battery is rated at about 5 h, so the session needs an external power bank. (Bortle 6, solid image; we allow 30% over the integration time.)
- USB-C power bank 10000mAh 5V 3A5 V 3 A input and it runs while charging.
- Seestar S30 Pro dew shieldActive anti-dew is built in; a shield adds margin. The S30 Pro front differs from the S30, so check the listing.
- red LED head torchRed light keeps your night vision; white light costs you twenty minutes of dark adaptation every time.
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Everything that fits the Seestar S30 Pro →
How it frames
The Cave Nebula is 50′ × 30′ across. The Seestar S30 Pro frames 3.99° × 2.24° at 3.74″ per pixel, so it fills 37% of the frame’s short side.
Longer subs
10, 20 and 30 s in Alt-Az; 60 s only in EQ mode, which needs the TH10 head. Time for a solid image by sub length:
| Sub length | Bortle 3 | Bortle 5 | Bortle 7 |
|---|---|---|---|
| 10 s | 3 h 22 min1,214 subs | 3 h 58 min1,427 subs | 6 h 33 min2,357 subs |
| 20 s | 2 h 19 min418 subs | 2 h 55 min524 subs | 5 h 30 min990 subs |
| 30 s | 1 h 58 min237 subs | 2 h 34 min308 subs | 5 h 09 min618 subs |
| 60 s | 1 h 37 min98 subs | 2 h 13 min133 subs | 4 h 48 min288 subs |
With and without the dual-band filter
| Filter | Bortle 3 | Bortle 5 | Bortle 7 |
|---|---|---|---|
| UV/IR-cut (no light-pollution filter) | 2 h 50 min1,021 subs | 4 h 46 min1,716 subs | 13 h4,754 subs |
| dual-band (LP filter) | 3 h 22 min1,214 subs | 3 h 58 min1,427 subs | 6 h 33 min2,357 subs |
About the Cave Nebula
A faint hydrogen arc with dark dust in Cepheus. Low surface brightness; this one wants dark skies and a long dual-band stack.
Sh2-155, Caldwell 9 · Emission nebula in Cepheus · magnitude 7.7 · 50′ × 30′ · best in Aug, Sep, Oct. Reachable from mid-northern latitudes (UK, northern US, central Europe) and from the south.
Emission nebulae glow in a few narrow lines, mostly hydrogen-alpha (deep red) and doubly ionised oxygen (teal). A dual-band filter passes those lines and blocks most skyglow, which is why it cuts the time needed from a suburban sky so dramatically. Use it. From a genuinely dark site the gain is smaller because there is less skyglow to block, and read noise becomes the limit, which is where longer subs (EQ mode, or Expert Mode on a Vespera) earn their keep.
Stars lose colour through a dual-band filter; a short broadband stack blended in fixes that if you care.
About the ZWO Seestar S30 Pro
The S30 optics upgraded to a quadruplet in front of an 8 MP IMX585. Same speed per pixel as the S30, four times the pixels, so you can crop hard.
10, 20 and 30 s in Alt-Az; 60 s only in EQ mode, which needs the TH10 head. Built-in UV/IR-cut, dual-band (OIII 30 nm / Hα 20 nm) and dark filters on the telephoto camera.
Longer subs matter most under dark skies, where read noise rather than skyglow sets the floor. From a city the difference between 10 s and 60 s subs is small; from a rural site it can halve the total time, especially with a dual-band filter in place.
Stack across nights. Every smart scope app can continue a stack or you can combine the saved frames on a computer; the figures here are totals, not single-session limits.
Have an image of the Cave Nebula from a Seestar S30 Pro? Email it with your total time and sky to [email protected] and it goes here, credited.
Same target, other telescopes
- Cave Nebula with the ZWO Seestar S50: 4 h from Bortle 6
- Cave Nebula with the ZWO Seestar S50 Pro: 4 h 30 min from Bortle 6
- Cave Nebula with the ZWO Seestar S30: 4 h 43 min from Bortle 6
- Cave Nebula with the DwarfLab DWARF 3: 4 h 52 min from Bortle 6
- Cave Nebula with the DwarfLab DWARF mini: 3 h 56 min from Bortle 6
- Cave Nebula with the DwarfLab Draco: 3 h 09 min from Bortle 6
- Cave Nebula with the DwarfLab DWARF II: 23 h from Bortle 6
- Cave Nebula with the Vaonis Vespera II: 6 h 37 min from Bortle 6
- Cave Nebula with the Vaonis Vespera Pro: 15 h from Bortle 6
- Cave Nebula with the Vaonis Vespera 3: 6 h 19 min from Bortle 6
- Cave Nebula with the Vaonis Vespera Pro 2: 14 h from Bortle 6
- Cave Nebula with the Unistellar eQuinox 2: 6 h 05 min from Bortle 6
- Cave Nebula with the Unistellar Odyssey: 28 h from Bortle 6
- Cave Nebula with the Celestron Origin: 1 h 45 min from Bortle 6
- Cave Nebula with the Celestron Origin Mark II: 2 h 23 min from Bortle 6
All telescopes for the Cave Nebula · All targets for the Seestar S30 Pro