How long to image the Cave Nebula with the DwarfLab DWARF mini
From a Bortle 6 suburban sky, the DwarfLab DWARF mini needs about 3 h 56 min (944 subs of 15 s with the built-in dual-band filter) for a solid image of the Cave Nebula. A quick look takes 59 min; a showpiece 16 h. Under a Bortle 3 rural sky the solid figure drops to 2 h 38 min. At Bortle 6 the limit is a mix of skyglow and read noise. In this scope's field it fills 70% 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 | 38 min151 subs | 2 h 30 min601 subs | 10 h2,403 subs |
| Bortle 2Typical dark site | 38 min153 subs | 2 h 33 min612 subs | 10 h2,445 subs |
| Bortle 3Rural | 39 min158 subs | 2 h 38 min631 subs | 11 h2,524 subs |
| Bortle 4Rural / suburban transition | 42 min170 subs | 2 h 50 min680 subs | 11 h2,717 subs |
| Bortle 5Suburban | 47 min189 subs | 3 h 09 min756 subs | 13 h3,023 subs |
| Bortle 6Bright suburban | 59 min236 subs | 3 h 56 min944 subs | 16 h3,773 subs |
| Bortle 7Suburban / urban transition | 1 h 21 min326 subs | 5 h 25 min1,301 subs | 22 h5,203 subs |
| Bortle 8City | 1 h 56 min464 subs | 7 h 44 min1,856 subs | 31 h7,423 subs |
| Bortle 9Inner city | 3 h 10 min760 subs | 13 h3,040 subs | 51 h12,158 subs |
Power and kit for this session
Allowing for slewing, focusing and rejected subs, that is about 5 h 07 min of run time. The DWARF mini’s battery is rated at about 3 h 30 min, so the session needs an external power bank. (Bortle 6, solid image; we allow 30% over the integration time.)
- USB-C PD power bank 10000mAh 20W7,000 mAh inside, about four hours; a PD bank extends the night.
- 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 DWARF mini →
How it frames
The Cave Nebula is 50′ × 30′ across. The DWARF mini frames 2.13° × 1.20° at 3.99″ per pixel, so it fills 70% of the frame’s short side.
Longer subs
Auto mode caps subs at 15 s; 30 s and longer need EQ mode, and 90 s is the ceiling. Time for a solid image by sub length:
| Sub length | Bortle 3 | Bortle 5 | Bortle 7 |
|---|---|---|---|
| 15 s | 2 h 38 min631 subs | 3 h 09 min756 subs | 5 h 25 min1,301 subs |
| 30 s | 1 h 51 min223 subs | 2 h 22 min285 subs | 4 h 38 min557 subs |
| 60 s | 1 h 28 min88 subs | 1 h 59 min119 subs | 4 h 15 min256 subs |
| 90 s | 1 h 20 min54 subs | 1 h 51 min75 subs | 4 h 07 min165 subs |
With and without the dual-band filter
| Filter | Bortle 3 | Bortle 5 | Bortle 7 |
|---|---|---|---|
| Astro (no light-pollution filter) | 2 h 20 min559 subs | 4 h 01 min966 subs | 11 h2,747 subs |
| dual-band | 2 h 38 min631 subs | 3 h 09 min756 subs | 5 h 25 min1,301 subs |
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 DwarfLab DWARF mini
DwarfLab’s answer to the Seestar S30: same sensor and focal length, big pixels, dual-band filter built in, and 90 s subs in EQ mode. Sensitivity over megapixels.
Auto mode caps subs at 15 s; 30 s and longer need EQ mode, and 90 s is the ceiling. Built-in Astro (430 to 690 nm), dark-frame and dual-band Hα / OIII filters; no plain VIS filter on the tele camera.
Longer subs matter most under dark skies, where read noise rather than skyglow sets the floor. From a city the difference between 15 s and 90 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 Cave Nebula from a DWARF mini? 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 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 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 DWARF mini