How long to image the Ghost of Cassiopeia with the DwarfLab Draco
From a Bortle 6 suburban sky, the DwarfLab Draco needs about 1 h 26 min (172 subs of 30 s with the built-in dual-narrowband (Hα + OIII) filter) for a solid image of the Ghost of Cassiopeia. A quick look takes 21 min; a showpiece 5 h 42 min. Under a Bortle 3 rural sky the solid figure drops to 59 min. At Bortle 6 the limit is a mix of skyglow and read noise. In this scope's field it fills 13% 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 | 14 min29 subs | 56 min113 subs | 3 h 44 min449 subs |
| Bortle 2Typical dark site | 14 min29 subs | 57 min115 subs | 3 h 48 min457 subs |
| Bortle 3Rural | 15 min30 subs | 59 min118 subs | 3 h 55 min470 subs |
| Bortle 4Rural / suburban transition | 16 min32 subs | 1 h 03 min126 subs | 4 h 12 min504 subs |
| Bortle 5Suburban | 17 min35 subs | 1 h 09 min139 subs | 4 h 38 min556 subs |
| Bortle 6Bright suburban | 21 min43 subs | 1 h 26 min172 subs | 5 h 42 min685 subs |
| Bortle 7Suburban / urban transition | 29 min59 subs | 1 h 56 min233 subs | 7 h 46 min932 subs |
| Bortle 8City | 41 min83 subs | 2 h 44 min329 subs | 11 h1,314 subs |
| Bortle 9Inner city | 1 h 07 min134 subs | 4 h 26 min533 subs | 18 h2,129 subs |
Power and kit for this session
Allowing for slewing, focusing and rejected subs, that is about 1 h 51 min of run time. The Draco’s battery (rated about 5 h) 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 20000mAhRated 5 h on its 10,000 mAh battery. DwarfLab has not published the charging input, so check PD support before relying on it mid-session.
- red LED head torchRed light keeps your night vision; white light costs you twenty minutes of dark adaptation every time.
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How it frames
The Ghost of Cassiopeia is 10′ × 3′ across. The Draco frames 1.66° × 1.24° at 1.46″ per pixel, so it fills 13% of the frame’s short side.
Longer subs
Auto Mode picks the exposure; Pro Mode allows up to 300 s, held by built-in guiding and field derotation. The 30 s default here is our assumption. Time for a solid image by sub length:
| Sub length | Bortle 3 | Bortle 5 | Bortle 7 |
|---|---|---|---|
| 30 s | 59 min118 subs | 1 h 09 min139 subs | 1 h 56 min233 subs |
| 60 s | 44 min44 subs | 54 min55 subs | 1 h 41 min102 subs |
| 120 s | 1 h30 subs | 1 h30 subs | 1 h 34 min47 subs |
| 300 s | 2 h 30 min30 subs | 2 h 30 min30 subs | 2 h 30 min30 subs |
With and without the dual-band filter
| Filter | Bortle 3 | Bortle 5 | Bortle 7 |
|---|---|---|---|
| No filter | 52 min104 subs | 1 h 27 min174 subs | 4 h481 subs |
| dual-narrowband (Hα + OIII) | 59 min118 subs | 1 h 09 min139 subs | 1 h 56 min233 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 Draco
DwarfLab’s big scope: 90 mm of folded f/3.8 optics, the most aperture of any Seestar or DWARF, a narrow 13 nm dual-band filter and 300 s subs with built-in guiding. A small-target scope; big nebulae need its mosaic mode.
Auto Mode picks the exposure; Pro Mode allows up to 300 s, held by built-in guiding and field derotation. The 30 s default here is our assumption. Built-in Hα + OIII dual-narrowband filter, 13 nm per line; the SHO Edition adds an SII option.
Longer subs matter most under dark skies, where read noise rather than skyglow sets the floor. From a city the difference between 30 s and 300 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 Draco? 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 3: 2 h 15 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 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 Draco