How long to image the Ghost of Cassiopeia with the DwarfLab DWARF 3
From a Bortle 6 suburban sky, the DwarfLab DWARF 3 needs about 2 h 15 min (539 subs of 15 s with the built-in dual-band filter) for a solid image of the Ghost of Cassiopeia. A quick look takes 34 min; a showpiece 8 h 58 min. Under a Bortle 3 rural sky the solid figure drops to 1 h 25 min. At Bortle 6 the limit is a mix of skyglow and read noise. In this scope's field it fills 10% 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 | 20 min80 subs | 1 h 20 min320 subs | 5 h 20 min1,279 subs |
| Bortle 2Typical dark site | 20 min82 subs | 1 h 22 min327 subs | 5 h 26 min1,306 subs |
| Bortle 3Rural | 21 min85 subs | 1 h 25 min340 subs | 5 h 39 min1,357 subs |
| Bortle 4Rural / suburban transition | 23 min93 subs | 1 h 32 min370 subs | 6 h 10 min1,480 subs |
| Bortle 5Suburban | 26 min105 subs | 1 h 45 min419 subs | 6 h 59 min1,675 subs |
| Bortle 6Bright suburban | 34 min135 subs | 2 h 15 min539 subs | 8 h 58 min2,154 subs |
| Bortle 7Suburban / urban transition | 48 min192 subs | 3 h 12 min767 subs | 13 h3,067 subs |
| Bortle 8City | 1 h 10 min281 subs | 4 h 40 min1,121 subs | 19 h4,483 subs |
| Bortle 9Inner city | 1 h 57 min470 subs | 7 h 49 min1,877 subs | 31 h7,505 subs |
Power and kit for this session
Allowing for slewing, focusing and rejected subs, that is about 2 h 55 min of run time. The DWARF 3’s battery (rated about 5 h 30 min) 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 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 Ghost of Cassiopeia is 10′ × 3′ across. The DWARF 3 frames 2.93° × 1.65° at 2.75″ per pixel, so it fills 10% 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 | 1 h 25 min340 subs | 1 h 45 min419 subs | 3 h 12 min767 subs |
| 30 s | 1 h 13 min147 subs | 1 h 33 min187 subs | 3 h361 subs |
| 60 s | 1 h 08 min68 subs | 1 h 27 min88 subs | 2 h 54 min175 subs |
With and without the dual-band filter
| Filter | Bortle 3 | Bortle 5 | Bortle 7 |
|---|---|---|---|
| Astro (no light-pollution filter) | 1 h 24 min338 subs | 2 h 29 min597 subs | 7 h 13 min1,734 subs |
| dual-band | 1 h 25 min340 subs | 1 h 45 min419 subs | 3 h 12 min767 subs |
About the Ghost of Cassiopeia
A small emission and reflection wisp being eroded by the star Gamma Cassiopeiae. Keep the bright star's glare under control.
IC 63 · Emission nebula in Cassiopeia · magnitude 10.0 · 10′ × 3′ · best in Sep, Oct, Nov. 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 Ghost of Cassiopeia from a DWARF 3? Email it with your total time and sky to [email protected] and it goes here, credited.
Same target, other telescopes
- Ghost of Cassiopeia with the ZWO Seestar S50: 1 h 48 min from Bortle 6
- Ghost of Cassiopeia with the ZWO Seestar S50 Pro: 2 h 01 min from Bortle 6
- Ghost of Cassiopeia with the ZWO Seestar S30: 2 h 06 min from Bortle 6
- Ghost of Cassiopeia with the ZWO Seestar S30 Pro: 2 h 11 min from Bortle 6
- Ghost of Cassiopeia with the DwarfLab DWARF mini: 1 h 46 min from Bortle 6
- Ghost of Cassiopeia with the DwarfLab Draco: 1 h 26 min from Bortle 6
- Ghost of Cassiopeia with the DwarfLab DWARF II: 9 h 43 min from Bortle 6
- Ghost of Cassiopeia with the Vaonis Vespera II: 2 h 50 min from Bortle 6
- Ghost of Cassiopeia with the Vaonis Vespera Pro: 6 h 21 min from Bortle 6
- Ghost of Cassiopeia with the Vaonis Vespera 3: 2 h 43 min from Bortle 6
- Ghost of Cassiopeia with the Vaonis Vespera Pro 2: 6 h 03 min from Bortle 6
- Ghost of Cassiopeia with the Unistellar eQuinox 2: 2 h 35 min from Bortle 6
- Ghost of Cassiopeia with the Unistellar Odyssey: 12 h from Bortle 6
- Ghost of Cassiopeia with the Celestron Origin: 45 min from Bortle 6
- Ghost of Cassiopeia with the Celestron Origin Mark II: 1 h 02 min from Bortle 6
All telescopes for the Ghost of Cassiopeia · All targets for the DWARF 3