How long to image the M21 with the Vaonis Vespera Pro
From a Bortle 6 suburban sky, the Vaonis Vespera Pro needs about 7 min (40 subs of 10 s) for a solid image of the M21. A quick look takes 2 min; a showpiece 26 min. Under a Bortle 3 rural sky the solid figure drops to 5 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 13% 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 min10 subs | 5 min30 subs | 15 min92 subs |
| Bortle 2Typical dark site | 2 min10 subs | 5 min30 subs | 16 min94 subs |
| Bortle 3Rural | 2 min10 subs | 5 min30 subs | 16 min98 subs |
| Bortle 4Rural / suburban transition | 2 min10 subs | 5 min30 subs | 18 min107 subs |
| Bortle 5Suburban | 2 min10 subs | 5 min31 subs | 20 min121 subs |
| Bortle 6Bright suburban | 2 min10 subs | 7 min40 subs | 26 min157 subs |
| Bortle 7Suburban / urban transition | 2 min15 subs | 9 min57 subs | 37 min225 subs |
| Bortle 8City | 3 min21 subs | 14 min83 subs | 55 min330 subs |
| Bortle 9Inner city | 6 min35 subs | 23 min139 subs | 1 h 32 min554 subs |
Power and kit for this session
Allowing for slewing, focusing and rejected subs, that is about 8 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 M21 is 13′ across. The Vespera Pro frames 1.62° × 1.62° at 1.65″ per pixel, so it fills 13% 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 | 5 min30 subs | 5 min31 subs | 9 min57 subs |
| 20 s | 10 min30 subs | 10 min30 subs | 10 min30 subs |
| 30 s | 15 min30 subs | 15 min30 subs | 15 min30 subs |
About the M21
A young open cluster beside the Trifid Nebula. Comes for free in a Trifid frame.
NGC 6531 · Open cluster in Sagittarius · magnitude 5.9 · 13′ · best in Jun, Jul, Aug. 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 M21 from a Vespera Pro? Email it with your total time and sky to [email protected] and it goes here, credited.
Same target, other telescopes
- M21 with the ZWO Seestar S50: 5 min from Bortle 6
- M21 with the ZWO Seestar S50 Pro: 5 min from Bortle 6
- M21 with the ZWO Seestar S30: 5 min from Bortle 6
- M21 with the ZWO Seestar S30 Pro: 5 min from Bortle 6
- M21 with the DwarfLab DWARF 3: 8 min from Bortle 6
- M21 with the DwarfLab DWARF mini: 8 min from Bortle 6
- M21 with the DwarfLab Draco: 15 min from Bortle 6
- M21 with the DwarfLab DWARF II: 9 min from Bortle 6
- M21 with the Vaonis Vespera II: 5 min from Bortle 6
- M21 with the Vaonis Vespera 3: 5 min from Bortle 6
- M21 with the Vaonis Vespera Pro 2: 6 min from Bortle 6
- M21 with the Unistellar eQuinox 2: 2 min from Bortle 6
- M21 with the Unistellar Odyssey: 10 min from Bortle 6
- M21 with the Celestron Origin: 5 min from Bortle 6
- M21 with the Celestron Origin Mark II: 5 min from Bortle 6
All telescopes for the M21 · All targets for the Vespera Pro