How long to image the Cave Nebula with the Unistellar eQuinox 2
From a Bortle 6 suburban sky, the Unistellar eQuinox 2 needs about 6 h 05 min (5,480 subs of 4 s) for a solid image of the Cave Nebula. A quick look takes 1 h 31 min; a showpiece 24 h. Under a Bortle 3 rural sky the solid figure drops to 3 h 26 min. At Bortle 6 the limit is a mix of skyglow and read noise. In this scope's field it is just over the frame at 1.5×.
| Sky | Quick lookTarget obvious, still noisy | SolidClean enough to share | ShowpieceSmooth faint detail, print-worthy |
|---|---|---|---|
| Bortle 1Excellent dark site | 48 min716 subs | 3 h 11 min2,863 subs | 13 h11,452 subs |
| Bortle 2Typical dark site | 49 min736 subs | 3 h 16 min2,944 subs | 13 h11,774 subs |
| Bortle 3Rural | 52 min774 subs | 3 h 26 min3,096 subs | 14 h12,382 subs |
| Bortle 4Rural / suburban transition | 58 min866 subs | 3 h 51 min3,464 subs | 15 h13,855 subs |
| Bortle 5Suburban | 1 h 07 min1,012 subs | 4 h 30 min4,048 subs | 18 h16,190 subs |
| Bortle 6Bright suburban | 1 h 31 min1,370 subs | 6 h 05 min5,480 subs | 24 h21,919 subs |
| Bortle 7Suburban / urban transition | 2 h 17 min2,053 subs | 9 h 07 min8,209 subs | 36 h32,836 subs |
| Bortle 8City | 3 h 27 min3,112 subs | 14 h12,447 subs | 55 h49,785 subs |
| Bortle 9Inner city | 5 h 58 min5,371 subs | 24 h21,484 subs | 95 h85,933 subs |
Power and kit for this session
Allowing for slewing, focusing and rejected subs, that is about 7 h 55 min of run time. That is more than one night: over 2 nights, about 3 h 57 min each. The eQuinox 2’s battery (rated about 11 h) should cover each night; 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 Cave Nebula is 50′ × 30′ across. The eQuinox 2 frames 0.76° × 0.57° at 1.33″ per pixel, so it is just over the frame at 1.5×. Point at the part you want; the edges will fall outside the frame.
Filters
The Cave Nebula is an emission target, where a dual-band filter would normally cut the time several-fold from a lit sky, but the eQuinox 2 has no dual-band option: 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 figures above are for the No filter position, and a darker sky is the lever that remains.
About the Cave Nebula
A faint hydrogen arc with dark dust in Cepheus. Low surface brightness; this one wants dark skies and a long dual-band stack.
Sh2-155, Caldwell 9 · Emission nebula in Cepheus · magnitude 7.7 · 50′ × 30′ · best in Aug, Sep, Oct. 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 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 Cave Nebula from a eQuinox 2? Email it with your total time and sky to [email protected] and it goes here, credited.
Same target, other telescopes
- Cave Nebula with the ZWO Seestar S50: 4 h from Bortle 6
- Cave Nebula with the ZWO Seestar S50 Pro: 4 h 30 min from Bortle 6
- Cave Nebula with the ZWO Seestar S30: 4 h 43 min from Bortle 6
- Cave Nebula with the ZWO Seestar S30 Pro: 4 h 51 min from Bortle 6
- Cave Nebula with the DwarfLab DWARF 3: 4 h 52 min from Bortle 6
- Cave Nebula with the DwarfLab DWARF mini: 3 h 56 min from Bortle 6
- Cave Nebula with the DwarfLab Draco: 3 h 09 min from Bortle 6
- Cave Nebula with the DwarfLab DWARF II: 23 h from Bortle 6
- Cave Nebula with the Vaonis Vespera II: 6 h 37 min from Bortle 6
- Cave Nebula with the Vaonis Vespera Pro: 15 h from Bortle 6
- Cave Nebula with the Vaonis Vespera 3: 6 h 19 min from Bortle 6
- Cave Nebula with the Vaonis Vespera Pro 2: 14 h from Bortle 6
- Cave Nebula with the Unistellar Odyssey: 28 h from Bortle 6
- Cave Nebula with the Celestron Origin: 1 h 45 min from Bortle 6
- Cave Nebula with the Celestron Origin Mark II: 2 h 23 min from Bortle 6
All telescopes for the Cave Nebula · All targets for the eQuinox 2