How long to image the Ghost of Cassiopeia with the ZWO Seestar S50
From a Bortle 6 suburban sky, the ZWO Seestar S50 needs about 1 h 48 min (649 subs of 10 s with the built-in dual-band (LP filter) filter) for a solid image of the Ghost of Cassiopeia. A quick look takes 27 min; a showpiece 7 h 12 min. Under a Bortle 3 rural sky the solid figure drops to 1 h 16 min. At Bortle 6 the limit is a mix of skyglow and read noise. In this scope's field it fills 23% 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 | 18 min110 subs | 1 h 13 min437 subs | 4 h 51 min1,745 subs |
| Bortle 2Typical dark site | 18 min111 subs | 1 h 14 min443 subs | 4 h 55 min1,771 subs |
| Bortle 3Rural | 19 min114 subs | 1 h 16 min455 subs | 5 h 03 min1,820 subs |
| Bortle 4Rural / suburban transition | 20 min122 subs | 1 h 21 min485 subs | 5 h 23 min1,940 subs |
| Bortle 5Suburban | 22 min134 subs | 1 h 29 min533 subs | 5 h 55 min2,129 subs |
| Bortle 6Bright suburban | 27 min163 subs | 1 h 48 min649 subs | 7 h 12 min2,594 subs |
| Bortle 7Suburban / urban transition | 36 min218 subs | 2 h 25 min870 subs | 9 h 40 min3,480 subs |
| Bortle 8City | 51 min304 subs | 3 h 22 min1,214 subs | 13 h4,856 subs |
| Bortle 9Inner city | 1 h 21 min487 subs | 5 h 25 min1,948 subs | 22 h7,790 subs |
Power and kit for this session
Allowing for slewing, focusing and rejected subs, that is about 2 h 20 min of run time. The Seestar S50’s battery (rated about 6 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 power bank 20000mAh 5V 3AThe S50 draws 5 V 3 A over USB-C and runs while charging; no PD needed.
- Seestar S50 dew shieldThe built-in heater copes with most nights; a shield helps in heavy dew and blocks stray light.
- 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 Seestar S50 →
How it frames
The Ghost of Cassiopeia is 10′ × 3′ across. The Seestar S50 frames 1.28° × 0.72° at 2.39″ per pixel, so it fills 23% of the frame’s short side.
Longer subs
10, 20 and 30 s in Alt-Az; 60 s only in EQ mode (app 2.5 and later). Time for a solid image by sub length:
| Sub length | Bortle 3 | Bortle 5 | Bortle 7 |
|---|---|---|---|
| 10 s | 1 h 16 min455 subs | 1 h 29 min533 subs | 2 h 25 min870 subs |
| 20 s | 56 min168 subs | 1 h 09 min206 subs | 2 h 05 min375 subs |
| 30 s | 49 min99 subs | 1 h 02 min124 subs | 1 h 58 min237 subs |
| 60 s | 42 min43 subs | 55 min56 subs | 1 h 51 min112 subs |
With and without the dual-band filter
| Filter | Bortle 3 | Bortle 5 | Bortle 7 |
|---|---|---|---|
| UV/IR-cut (no light-pollution filter) | 1 h 05 min389 subs | 1 h 47 min642 subs | 4 h 51 min1,745 subs |
| dual-band (LP filter) | 1 h 16 min455 subs | 1 h 29 min533 subs | 2 h 25 min870 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 ZWO Seestar S50
The scope that made smart astrophotography mainstream. 50 mm triplet, 2 MP sensor, dual-band filter on a wheel. Alt-Az stacking at 10 s, EQ mode unlocks 60 s. Out of production since 2026 and replaced by the S50 Pro, but there are a great many in use.
10, 20 and 30 s in Alt-Az; 60 s only in EQ mode (app 2.5 and later). Built-in dual-band light-pollution filter, switchable in the app.
Longer subs matter most under dark skies, where read noise rather than skyglow sets the floor. From a city the difference between 10 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 Seestar S50? 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 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 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 Seestar S50