How long to image the Cave Nebula with the Unistellar Odyssey
From a Bortle 6 suburban sky, the Unistellar Odyssey needs about 28 h (25,527 subs of 4 s) for a solid image of the Cave Nebula. A quick look takes 7 h 05 min; a showpiece 110+ h. Under a Bortle 3 rural sky the solid figure drops to 19 h. 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 | 4 h 27 min4,002 subs | 18 h16,006 subs | 71 h64,024 subs |
| Bortle 2Typical dark site | 4 h 32 min4,075 subs | 18 h16,299 subs | 72 h65,194 subs |
| Bortle 3Rural | 4 h 41 min4,213 subs | 19 h16,852 subs | 75 h67,406 subs |
| Bortle 4Rural / suburban transition | 5 h 03 min4,548 subs | 20 h18,192 subs | 81 h72,767 subs |
| Bortle 5Suburban | 5 h 39 min5,079 subs | 23 h20,316 subs | 90 h81,262 subs |
| Bortle 6Bright suburban | 7 h 05 min6,382 subs | 28 h25,527 subs | 110+ h102,107 subs |
| Bortle 7Suburban / urban transition | 9 h 51 min8,865 subs | 39 h35,457 subs | 160+ h141,825 subs |
| Bortle 8City | 14 h12,719 subs | 57 h50,873 subs | 230+ h203,492 subs |
| Bortle 9Inner city | 23 h20,939 subs | 93 h83,753 subs | 370+ h335,011 subs |
Power and kit for this session
Allowing for slewing, focusing and rejected subs, that is about 37 h of run time. That is more than one night: over 6 nights, about 6 h 09 min each. The Odyssey’s battery is rated at about 5 h, so each night needs an external power bank. (Bortle 6, solid image; we allow 30% over the integration time.)
- USB power bank 20000mAh 5V 2.4AUnistellar says plain 5 V 2.4 A and warns against fast or adaptive chargers.
- 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 Odyssey →
How it frames
The Cave Nebula is 50′ × 30′ across. The Odyssey frames 0.75° × 0.56° at 0.93″ 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 Odyssey has no dual-band option: No filter option; Unistellar says third-party filters cannot be fitted to the Odyssey. 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 Odyssey
Unistellar’s compact 85 mm with autofocus and tiny pixels. Sharp, but the fine sampling costs time on faint extended targets. The Odyssey Pro is the same telescope with an eyepiece added, so these figures apply to both.
Fixed 4 s subs in Enhanced Vision; they cannot be changed. No filter option; Unistellar says third-party filters cannot be fitted to the Odyssey.
The Odyssey 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 Odyssey? 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 eQuinox 2: 6 h 05 min 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 Odyssey