How long to image the NGC 6939 with the Vaonis Vespera Pro
From a Bortle 6 suburban sky, the Vaonis Vespera Pro needs about 12 min (73 subs of 10 s) for a solid image of the NGC 6939. A quick look takes 3 min; a showpiece 48 min. Under a Bortle 3 rural sky the solid figure drops to 8 min. At Bortle 6 the limit is skyglow, so a darker site or a filter helps more than longer subs. 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 | 2 min11 subs | 7 min43 subs | 28 min170 subs |
| Bortle 2Typical dark site | 2 min11 subs | 7 min44 subs | 29 min174 subs |
| Bortle 3Rural | 2 min12 subs | 8 min46 subs | 30 min181 subs |
| Bortle 4Rural / suburban transition | 2 min13 subs | 8 min50 subs | 33 min198 subs |
| Bortle 5Suburban | 2 min15 subs | 9 min57 subs | 37 min225 subs |
| Bortle 6Bright suburban | 3 min19 subs | 12 min73 subs | 48 min291 subs |
| Bortle 7Suburban / urban transition | 4 min27 subs | 17 min105 subs | 1 h 09 min417 subs |
| Bortle 8City | 6 min39 subs | 25 min153 subs | 1 h 42 min612 subs |
| Bortle 9Inner city | 11 min65 subs | 43 min257 subs | 2 h 51 min1,028 subs |
Power and kit for this session
Allowing for slewing, focusing and rejected subs, that is about 16 min of run time. The Vespera Pro’s battery (rated about 11 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 20000mAh 30WExtends the 11 h battery; 30 W PD per Vaonis.
- 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 Vespera Pro →
How it frames
The NGC 6939 is 7′ across. The Vespera Pro frames 1.62° × 1.62° at 1.65″ per pixel, so it fills 7% of the frame’s short side.
Longer subs
10 s subs by default; Expert Mode manual targets allow 1 to 30 s. Alt-azimuth only, no EQ mode. Time for a solid image by sub length:
| Sub length | Bortle 3 | Bortle 5 | Bortle 7 |
|---|---|---|---|
| 10 s | 8 min46 subs | 9 min57 subs | 17 min105 subs |
| 20 s | 10 min30 subs | 10 min30 subs | 17 min51 subs |
| 30 s | 15 min30 subs | 15 min30 subs | 17 min34 subs |
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 Vaonis Vespera Pro
The square-sensor Vespera with 2 µm pixels. Higher resolution than the II, and correspondingly slower per pixel: expect around double the time for the same per-pixel SNR. Run-out in 2026 and replaced by the Vespera Pro 2.
10 s subs by default; Expert Mode manual targets allow 1 to 30 s. Alt-azimuth only, no EQ mode. Optional clip-on Vaonis filters: dual-band, light-pollution (CLS) and solar.
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 30 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 6939 from a Vespera Pro? 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 DwarfLab DWARF II: 18 min from Bortle 6
- NGC 6939 with the Vaonis Vespera II: 6 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 Vespera Pro