How long to image the NGC 6781 with the DwarfLab DWARF 3
From a Bortle 6 suburban sky, the DwarfLab DWARF 3 needs about 3 h 22 min (808 subs of 15 s with the built-in dual-band filter) for a solid image of the NGC 6781. A quick look takes 50 min; a showpiece 13 h. Under a Bortle 3 rural sky the solid figure drops to 2 h 07 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 39 pixels across.
| Sky | Quick lookTarget obvious, still noisy | SolidClean enough to share | ShowpieceSmooth faint detail, print-worthy |
|---|---|---|---|
| Bortle 1Excellent dark site | 30 min120 subs | 2 h480 subs | 8 h1,919 subs |
| Bortle 2Typical dark site | 31 min123 subs | 2 h 02 min490 subs | 8 h 10 min1,959 subs |
| Bortle 3Rural | 32 min128 subs | 2 h 07 min509 subs | 8 h 29 min2,035 subs |
| Bortle 4Rural / suburban transition | 35 min139 subs | 2 h 19 min555 subs | 9 h 15 min2,220 subs |
| Bortle 5Suburban | 39 min158 subs | 2 h 37 min629 subs | 10 h2,513 subs |
| Bortle 6Bright suburban | 50 min202 subs | 3 h 22 min808 subs | 13 h3,231 subs |
| Bortle 7Suburban / urban transition | 1 h 12 min288 subs | 4 h 47 min1,150 subs | 19 h4,600 subs |
| Bortle 8City | 1 h 45 min421 subs | 7 h1,682 subs | 28 h6,725 subs |
| Bortle 9Inner city | 2 h 56 min704 subs | 12 h2,815 subs | 47 h11,257 subs |
Power and kit for this session
Allowing for slewing, focusing and rejected subs, that is about 4 h 22 min of run time. The DWARF 3’s battery (rated about 5 h 30 min) 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 PD power bank 20000mAh 18W18 W PD input and it runs while charging; needs a C-to-C cable for PD.
- 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 DWARF 3 →
How it frames
The NGC 6781 is 1.8′ across. The DWARF 3 frames 2.93° × 1.65° at 2.75″ per pixel, so it is small in the frame, about 39 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
Auto mode caps subs at 15 s; 30 s and longer need EQ mode, and 60 s is the ceiling on the tele camera. Time for a solid image by sub length:
| Sub length | Bortle 3 | Bortle 5 | Bortle 7 |
|---|---|---|---|
| 15 s | 2 h 07 min509 subs | 2 h 37 min629 subs | 4 h 47 min1,150 subs |
| 30 s | 1 h 50 min220 subs | 2 h 20 min280 subs | 4 h 30 min541 subs |
| 60 s | 1 h 41 min102 subs | 2 h 11 min132 subs | 4 h 22 min262 subs |
With and without the dual-band filter
| Filter | Bortle 3 | Bortle 5 | Bortle 7 |
|---|---|---|---|
| Astro (no light-pollution filter) | 2 h 06 min506 subs | 3 h 44 min896 subs | 11 h2,600 subs |
| dual-band | 2 h 07 min509 subs | 2 h 37 min629 subs | 4 h 47 min1,150 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 DwarfLab DWARF 3
Small pixels on a 35 mm f/4.3 lens give a sharper image than its aperture suggests, and EQ mode with 60 s subs makes it the read-noise winner in dark skies.
Auto mode caps subs at 15 s; 30 s and longer need EQ mode, and 60 s is the ceiling on the tele camera. Three built-in filters: VIS, Astro (430 to 690 nm) and dual-band Hα 656 nm / OIII 501 nm.
Longer subs matter most under dark skies, where read noise rather than skyglow sets the floor. From a city the difference between 15 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 DWARF 3? 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: 3 h 09 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 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 DWARF 3