How long to image the Crescent Nebula with the Vaonis Vespera II
From a Bortle 6 suburban sky, the Vaonis Vespera II needs about 4 h 37 min (1,661 subs of 10 s) for a solid image of the Crescent Nebula. A quick look takes 1 h 09 min; a showpiece 18 h. Under a Bortle 3 rural sky the solid figure drops to 1 h 40 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 21% 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 | 21 min125 subs | 1 h 23 min499 subs | 5 h 32 min1,995 subs |
| Bortle 2Typical dark site | 22 min134 subs | 1 h 29 min535 subs | 5 h 56 min2,137 subs |
| Bortle 3Rural | 25 min151 subs | 1 h 40 min602 subs | 6 h 41 min2,407 subs |
| Bortle 4Rural / suburban transition | 32 min192 subs | 2 h 08 min766 subs | 8 h 30 min3,061 subs |
| Bortle 5Suburban | 43 min257 subs | 2 h 51 min1,025 subs | 11 h4,098 subs |
| Bortle 6Bright suburban | 1 h 09 min416 subs | 4 h 37 min1,661 subs | 18 h6,642 subs |
| Bortle 7Suburban / urban transition | 2 h719 subs | 7 h 59 min2,873 subs | 32 h11,489 subs |
| Bortle 8City | 3 h 18 min1,189 subs | 13 h4,754 subs | 53 h19,014 subs |
| Bortle 9Inner city | 6 h 05 min2,192 subs | 24 h8,766 subs | 97 h35,064 subs |
Power and kit for this session
Allowing for slewing, focusing and rejected subs, that is about 6 h of run time. The Vespera II’s battery is rated at about 4 h, so the session needs an external power bank. (Bortle 6, solid image; we allow 30% over the integration time.)
- USB-C PD power bank 20000mAh 30WOnly four hours inside; Vaonis specifies a 30 W PD source. C-to-C cable not included.
- Vaonis Vespera hygrometer sensorTriggers the built-in demister automatically; the correct dew accessory for the II.
- 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 II →
How it frames
The Crescent Nebula is 18′ × 12′ across. The Vespera II frames 2.55° × 1.44° at 2.39″ per pixel, so it fills 21% 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 | 1 h 40 min602 subs | 2 h 51 min1,025 subs | 7 h 59 min2,873 subs |
| 20 s | 1 h 24 min252 subs | 2 h 34 min463 subs | 7 h 42 min1,387 subs |
| 30 s | 1 h 18 min157 subs | 2 h 29 min298 subs | 7 h 37 min914 subs |
With and without the dual-band filter
| Filter | Bortle 3 | Bortle 5 | Bortle 7 |
|---|---|---|---|
| No filter | 1 h 40 min602 subs | 2 h 51 min1,025 subs | 7 h 59 min2,873 subs |
| dual-band (Dual Band filter), clip-on | 1 h 55 min692 subs | 2 h 17 min821 subs | 3 h 51 min1,387 subs |
The Vespera II has no built-in dual-band filter. Optional clip-on Vaonis filters: dual-band, light-pollution (CLS) and solar; the app detects which is fitted. On an emission target like this it is the single biggest upgrade you can make.
About the Crescent Nebula
A shell blown by a Wolf-Rayet star, bright in H-alpha with a faint OIII skin. Small, so the bigger scopes do it justice.
NGC 6888, Caldwell 27 · Emission nebula in Cygnus · magnitude 7.4 · 18′ × 12′ · best in Jul, Aug, Sep. 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 Vaonis Vespera II
A 50 mm quadruplet on an 8 MP sensor with Vaonis’s mosaic mode for wide fields. Same optics class as the Seestar S50, four times the pixels.
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; the app detects which is fitted.
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 Crescent Nebula from a Vespera II? Email it with your total time and sky to [email protected] and it goes here, credited.
Same target, other telescopes
- Crescent Nebula with the ZWO Seestar S50: 2 h 49 min from Bortle 6
- Crescent Nebula with the ZWO Seestar S50 Pro: 3 h 10 min from Bortle 6
- Crescent Nebula with the ZWO Seestar S30: 3 h 19 min from Bortle 6
- Crescent Nebula with the ZWO Seestar S30 Pro: 3 h 25 min from Bortle 6
- Crescent Nebula with the DwarfLab DWARF 3: 3 h 27 min from Bortle 6
- Crescent Nebula with the DwarfLab DWARF mini: 2 h 47 min from Bortle 6
- Crescent Nebula with the DwarfLab Draco: 2 h 14 min from Bortle 6
- Crescent Nebula with the DwarfLab DWARF II: 16 h from Bortle 6
- Crescent Nebula with the Vaonis Vespera Pro: 10 h from Bortle 6
- Crescent Nebula with the Vaonis Vespera 3: 4 h 24 min from Bortle 6
- Crescent Nebula with the Vaonis Vespera Pro 2: 9 h 52 min from Bortle 6
- Crescent Nebula with the Unistellar eQuinox 2: 4 h 14 min from Bortle 6
- Crescent Nebula with the Unistellar Odyssey: 20 h from Bortle 6
- Crescent Nebula with the Celestron Origin: 1 h 13 min from Bortle 6
- Crescent Nebula with the Celestron Origin Mark II: 1 h 40 min from Bortle 6
All telescopes for the Crescent Nebula · All targets for the Vespera II