How long to image the NGC 6939 with the DwarfLab DWARF II
From a Bortle 6 suburban sky, the DwarfLab DWARF II needs about 18 min (71 subs of 15 s) for a solid image of the NGC 6939. A quick look takes 4 min; a showpiece 1 h 11 min. Under a Bortle 3 rural sky the solid figure drops to 12 min. At Bortle 6 the limit is a mix of skyglow and read noise. In this scope's field it fills 7% 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 | 3 min12 subs | 11 min45 subs | 44 min177 subs |
| Bortle 2Typical dark site | 3 min12 subs | 11 min45 subs | 45 min180 subs |
| Bortle 3Rural | 3 min12 subs | 12 min47 subs | 46 min186 subs |
| Bortle 4Rural / suburban transition | 3 min13 subs | 13 min51 subs | 50 min201 subs |
| Bortle 5Suburban | 4 min15 subs | 14 min57 subs | 56 min225 subs |
| Bortle 6Bright suburban | 4 min18 subs | 18 min71 subs | 1 h 11 min283 subs |
| Bortle 7Suburban / urban transition | 6 min25 subs | 25 min99 subs | 1 h 38 min393 subs |
| Bortle 8City | 9 min36 subs | 35 min142 subs | 2 h 21 min565 subs |
| Bortle 9Inner city | 15 min59 subs | 58 min233 subs | 3 h 53 min932 subs |
Power and kit for this session
Allowing for slewing, focusing and rejected subs, that is about 23 min of run time. The DWARF II’s battery (rated about 3 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 PD power bank 10000mAh 18W18 W PD input; runs while charging.
- 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 II →
How it frames
The NGC 6939 is 7′ across. The DWARF II frames 3.19° × 1.79° at 2.99″ per pixel, so it fills 7% of the frame’s short side.
About the NGC 6939
A rich, old open cluster that shares a frame with the Fireworks Galaxy. Cluster and galaxy in one shot.
Cep open cluster · Open cluster in Cepheus · magnitude 7.8 · 7′ · best in Jul, Aug, Sep. Reachable from mid-northern latitudes (UK, northern US, central Europe) and from the south.
Open clusters are the easiest targets in the sky. The stars are bright, so the aim is colour and tight stars rather than depth: short subs, no filter, and stop before the bright members saturate. The nominal time here gets you clean star colour; more integration only adds background stars.
About the DwarfLab DWARF II
The original pocket scope. 24 mm aperture and tiny 1.45 µm pixels mean it is slow per pixel, so bin or downsample and be patient.
15 s is the hard maximum in any mode; DwarfLab recommends EQ mode at 15 s. Two built-in filters, VIS and Astro (IR-pass); no dual-band. The optional UHC filter is no longer sold.
The DWARF II uses fixed 15 s subs, so the only levers you have are the sky you shoot from, the filter, and total time.
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 6939 from a DWARF II? Email it with your total time and sky to [email protected] and it goes here, credited.
Same target, other telescopes
- NGC 6939 with the ZWO Seestar S50: 6 min from Bortle 6
- NGC 6939 with the ZWO Seestar S50 Pro: 6 min from Bortle 6
- NGC 6939 with the ZWO Seestar S30: 6 min from Bortle 6
- NGC 6939 with the ZWO Seestar S30 Pro: 6 min from Bortle 6
- NGC 6939 with the DwarfLab DWARF 3: 8 min from Bortle 6
- NGC 6939 with the DwarfLab DWARF mini: 8 min from Bortle 6
- NGC 6939 with the DwarfLab Draco: 15 min from Bortle 6
- NGC 6939 with the Vaonis Vespera II: 6 min from Bortle 6
- NGC 6939 with the Vaonis Vespera Pro: 12 min from Bortle 6
- NGC 6939 with the Vaonis Vespera 3: 5 min from Bortle 6
- NGC 6939 with the Vaonis Vespera Pro 2: 12 min from Bortle 6
- NGC 6939 with the Unistellar eQuinox 2: 4 min from Bortle 6
- NGC 6939 with the Unistellar Odyssey: 19 min from Bortle 6
- NGC 6939 with the Celestron Origin: 5 min from Bortle 6
- NGC 6939 with the Celestron Origin Mark II: 5 min from Bortle 6
All telescopes for the NGC 6939 · All targets for the DWARF II