How long to image the M21 with the Unistellar eQuinox 2
From a Bortle 6 suburban sky, the Unistellar eQuinox 2 needs about 2 min (36 subs of 4 s) for a solid image of the M21. A quick look takes < 1 min; a showpiece 10 min. Under a Bortle 3 rural sky the solid figure drops to 2 min. At Bortle 6 the limit is a mix of skyglow and read noise. In this scope's field it fills 38% 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 | < 1 min10 subs | 2 min30 subs | 6 min96 subs |
| Bortle 2Typical dark site | < 1 min10 subs | 2 min30 subs | 6 min98 subs |
| Bortle 3Rural | < 1 min10 subs | 2 min30 subs | 7 min101 subs |
| Bortle 4Rural / suburban transition | < 1 min10 subs | 2 min30 subs | 7 min107 subs |
| Bortle 5Suburban | < 1 min10 subs | 2 min30 subs | 8 min118 subs |
| Bortle 6Bright suburban | < 1 min10 subs | 2 min36 subs | 10 min144 subs |
| Bortle 7Suburban / urban transition | < 1 min13 subs | 3 min49 subs | 13 min194 subs |
| Bortle 8City | 1 min17 subs | 5 min68 subs | 18 min272 subs |
| Bortle 9Inner city | 2 min28 subs | 7 min110 subs | 29 min438 subs |
Power and kit for this session
Allowing for slewing, focusing and rejected subs, that is about 3 min of run time. The eQuinox 2’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 power bank 20000mAh 5V 2AUnistellar asks for a 5 V 2 A output; PD is not needed.
- 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 eQuinox 2 →
How it frames
The M21 is 13′ across. The eQuinox 2 frames 0.76° × 0.57° at 1.33″ per pixel, so it fills 38% of the frame’s short side.
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 Unistellar eQuinox 2
A 114 mm Newtonian with five times the light grasp of a 50 mm refractor. Fixed 4 s subs put it in read-noise territory under dark skies, but the aperture carries it. The published field is 45.6′ × 34.2′, a crop of the sensor.
Fixed 4 s subs in Enhanced Vision; they cannot be changed. No built-in filter. Unistellar sells only a solar filter and says a third-party filter is at your own risk and voids the warranty.
The eQuinox 2 uses fixed 4 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 M21 from a eQuinox 2? 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 Pro: 7 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 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