How long to image the NGC 6781 with the ZWO Seestar S30
From a Bortle 6 suburban sky, the ZWO Seestar S30 needs about 3 h 09 min (1,132 subs of 10 s with the built-in dual-band (LP filter) filter) for a solid image of the NGC 6781. A quick look takes 47 min; a showpiece 13 h. Under a Bortle 3 rural sky the solid figure drops to 2 h 20 min. At Bortle 6 the limit is a mix of skyglow and read noise. In this scope's field it is small in the frame, about 27 pixels across.
| Sky | Quick lookTarget obvious, still noisy | SolidClean enough to share | ShowpieceSmooth faint detail, print-worthy |
|---|---|---|---|
| Bortle 1Excellent dark site | 34 min204 subs | 2 h 16 min814 subs | 9 h 02 min3,254 subs |
| Bortle 2Typical dark site | 34 min206 subs | 2 h 17 min824 subs | 9 h 09 min3,293 subs |
| Bortle 3Rural | 35 min211 subs | 2 h 20 min842 subs | 9 h 21 min3,367 subs |
| Bortle 4Rural / suburban transition | 37 min222 subs | 2 h 28 min887 subs | 9 h 51 min3,546 subs |
| Bortle 5Suburban | 40 min240 subs | 2 h 40 min958 subs | 11 h3,831 subs |
| Bortle 6Bright suburban | 47 min283 subs | 3 h 09 min1,132 subs | 13 h4,528 subs |
| Bortle 7Suburban / urban transition | 1 h 01 min367 subs | 4 h 04 min1,465 subs | 16 h5,857 subs |
| Bortle 8City | 1 h 23 min496 subs | 5 h 30 min1,981 subs | 22 h7,921 subs |
| Bortle 9Inner city | 2 h 08 min771 subs | 8 h 33 min3,081 subs | 34 h12,322 subs |
Power and kit for this session
Allowing for slewing, focusing and rejected subs, that is about 4 h 05 min of run time. The Seestar S30’s battery (rated about 6 h) should cover it; a power bank still keeps the phone running the app alive. (Bortle 6, solid image; we allow 30% over the integration time.)
- USB-C power bank 10000mAh 5V 3A6,000 mAh inside; a 10,000 mAh 5 V 3 A bank roughly doubles a session.
- Seestar S30 dew shieldHeater is built in; a cheap shield reduces dew and stray light.
- red LED head torchRed light keeps your night vision; white light costs you twenty minutes of dark adaptation every time.
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How it frames
The NGC 6781 is 1.8′ across. The Seestar S30 frames 2.13° × 1.20° at 3.99″ per pixel, so it is small in the frame, about 27 pixels across. It is worth doing, but the result is a crop rather than a full frame; a longer focal length would resolve more of it.
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 | 2 h 20 min842 subs | 2 h 40 min958 subs | 4 h 04 min1,465 subs |
| 20 s | 1 h 37 min291 subs | 1 h 56 min349 subs | 3 h 21 min602 subs |
| 30 s | 1 h 22 min165 subs | 1 h 42 min204 subs | 3 h 06 min373 subs |
| 60 s | 1 h 08 min68 subs | 1 h 27 min88 subs | 2 h 52 min172 subs |
With and without the dual-band filter
| Filter | Bortle 3 | Bortle 5 | Bortle 7 |
|---|---|---|---|
| UV/IR-cut (no light-pollution filter) | 1 h 50 min662 subs | 2 h 53 min1,040 subs | 7 h 29 min2,695 subs |
| dual-band (LP filter) | 2 h 20 min842 subs | 2 h 40 min958 subs | 4 h 04 min1,465 subs |
About the NGC 6781
A ghostly ring planetary in Aquila, larger and fainter than the Ring Nebula. Dual-band recommended.
Aquila planetary · Planetary nebula in Aquila · magnitude 11.4 · 1.8′ · best in Jun, Jul, Aug. Reachable from mid-northern latitudes (UK, northern US, central Europe) and from the south.
Planetary nebulae are small but intensely bright per pixel in OIII and H-alpha, so they respond very well to a dual-band filter and do not need much time for the main shell. The faint outer halos most of them have are a different proposition and need hours. Keep subs short if the central region saturates.
About the ZWO Seestar S30
Wider and lighter than the S50 with the same 2.9 µm pixels, so its per-pixel speed on extended targets is close despite the smaller aperture. Ideal for big nebulae.
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.
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 NGC 6781 from a Seestar S30? Email it with your total time and sky to [email protected] and it goes here, credited.
Same target, other telescopes
- NGC 6781 with the ZWO Seestar S50: 2 h 42 min from Bortle 6
- NGC 6781 with the ZWO Seestar S50 Pro: 3 h 02 min from Bortle 6
- NGC 6781 with the ZWO Seestar S30 Pro: 3 h 16 min from Bortle 6
- NGC 6781 with the DwarfLab DWARF 3: 3 h 22 min from Bortle 6
- NGC 6781 with the DwarfLab DWARF mini: 2 h 40 min from Bortle 6
- NGC 6781 with the DwarfLab Draco: 2 h 08 min from Bortle 6
- NGC 6781 with the DwarfLab DWARF II: 15 h from Bortle 6
- NGC 6781 with the Vaonis Vespera II: 4 h 15 min from Bortle 6
- NGC 6781 with the Vaonis Vespera Pro: 9 h 32 min from Bortle 6
- NGC 6781 with the Vaonis Vespera 3: 4 h 04 min from Bortle 6
- NGC 6781 with the Vaonis Vespera Pro 2: 9 h 05 min from Bortle 6
- NGC 6781 with the Unistellar eQuinox 2: 3 h 52 min from Bortle 6
- NGC 6781 with the Unistellar Odyssey: 18 h from Bortle 6
- NGC 6781 with the Celestron Origin: 1 h 07 min from Bortle 6
- NGC 6781 with the Celestron Origin Mark II: 1 h 33 min from Bortle 6
All telescopes for the NGC 6781 · All targets for the Seestar S30