How long to image the Cave Nebula with the DwarfLab DWARF 3
From a Bortle 6 suburban sky, the DwarfLab DWARF 3 needs about 4 h 52 min (1,169 subs of 15 s with the built-in dual-band filter) for a solid image of the Cave Nebula. A quick look takes 1 h 13 min; a showpiece 19 h. Under a Bortle 3 rural sky the solid figure drops to 2 h 51 min. At Bortle 6 the limit is a mix of skyglow and read noise. In this scope's field it fills 51% 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 | 40 min160 subs | 2 h 40 min639 subs | 11 h2,555 subs |
| Bortle 2Typical dark site | 41 min164 subs | 2 h 44 min655 subs | 11 h2,620 subs |
| Bortle 3Rural | 43 min172 subs | 2 h 51 min686 subs | 11 h2,743 subs |
| Bortle 4Rural / suburban transition | 48 min191 subs | 3 h 10 min761 subs | 13 h3,041 subs |
| Bortle 5Suburban | 55 min220 subs | 3 h 40 min879 subs | 15 h3,514 subs |
| Bortle 6Bright suburban | 1 h 13 min293 subs | 4 h 52 min1,169 subs | 19 h4,673 subs |
| Bortle 7Suburban / urban transition | 1 h 48 min431 subs | 7 h 10 min1,721 subs | 29 h6,881 subs |
| Bortle 8City | 2 h 41 min645 subs | 11 h2,578 subs | 43 h10,310 subs |
| Bortle 9Inner city | 4 h 35 min1,102 subs | 18 h4,406 subs | 73 h17,624 subs |
Power and kit for this session
Allowing for slewing, focusing and rejected subs, that is about 6 h 20 min of run time. The DWARF 3’s battery is rated at about 5 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 20000mAh 18W18 W PD input and it runs while charging; needs a C-to-C cable for PD.
- 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 3 →
How it frames
The Cave Nebula is 50′ × 30′ across. The DWARF 3 frames 2.93° × 1.65° at 2.75″ per pixel, so it fills 51% of the frame’s short side.
Longer subs
Auto mode caps subs at 15 s; 30 s and longer need EQ mode, and 60 s is the ceiling on the tele camera. Time for a solid image by sub length:
| Sub length | Bortle 3 | Bortle 5 | Bortle 7 |
|---|---|---|---|
| 15 s | 2 h 51 min686 subs | 3 h 40 min879 subs | 7 h 10 min1,721 subs |
| 30 s | 2 h 24 min288 subs | 3 h 12 min384 subs | 6 h 42 min805 subs |
| 60 s | 2 h 10 min130 subs | 2 h 58 min178 subs | 6 h 28 min389 subs |
With and without the dual-band filter
| Filter | Bortle 3 | Bortle 5 | Bortle 7 |
|---|---|---|---|
| Astro (no light-pollution filter) | 3 h722 subs | 5 h 38 min1,351 subs | 17 h4,101 subs |
| dual-band | 2 h 51 min686 subs | 3 h 40 min879 subs | 7 h 10 min1,721 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 3
Small pixels on a 35 mm f/4.3 lens give a sharper image than its aperture suggests, and EQ mode with 60 s subs makes it the read-noise winner in dark skies.
Auto mode caps subs at 15 s; 30 s and longer need EQ mode, and 60 s is the ceiling on the tele camera. Three built-in filters: VIS, Astro (430 to 690 nm) and dual-band Hα 656 nm / OIII 501 nm.
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 60 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 3? 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 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 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 3