How long to image the Ghost of Cassiopeia with the ZWO Seestar S50 Pro
From a Bortle 6 suburban sky, the ZWO Seestar S50 Pro needs about 2 h 01 min (727 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 30 min; a showpiece 8 h 05 min. Under a Bortle 3 rural sky the solid figure drops to 1 h 26 min. At Bortle 6 the limit is a mix of skyglow and read noise. In this scope's field it fills 12% 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 | 21 min125 subs | 1 h 23 min498 subs | 5 h 31 min1,989 subs |
| Bortle 2Typical dark site | 21 min127 subs | 1 h 24 min505 subs | 5 h 36 min2,017 subs |
| Bortle 3Rural | 22 min130 subs | 1 h 26 min518 subs | 5 h 45 min2,071 subs |
| Bortle 4Rural / suburban transition | 23 min138 subs | 1 h 32 min550 subs | 6 h 07 min2,200 subs |
| Bortle 5Suburban | 25 min151 subs | 1 h 40 min602 subs | 6 h 41 min2,405 subs |
| Bortle 6Bright suburban | 30 min182 subs | 2 h 01 min727 subs | 8 h 05 min2,908 subs |
| Bortle 7Suburban / urban transition | 40 min242 subs | 2 h 41 min967 subs | 11 h3,866 subs |
| Bortle 8City | 56 min335 subs | 3 h 43 min1,339 subs | 15 h5,354 subs |
| Bortle 9Inner city | 1 h 29 min533 subs | 5 h 55 min2,132 subs | 24 h8,528 subs |
Power and kit for this session
Allowing for slewing, focusing and rejected subs, that is about 2 h 37 min of run time. The Seestar S50 Pro’s battery (rated about 9 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 20000mAh 30WAccepts 12 V 3 A PD, so a 30 W bank tops up the 10,000 mAh cell while imaging.
- Seestar S50 Pro dew shieldDew heater is built in; a shield adds margin on damp nights. Check the listing says S50 Pro.
- 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 Pro →
How it frames
The Ghost of Cassiopeia is 10′ × 3′ across. The Seestar S50 Pro frames 2.45° × 1.38° at 2.30″ per pixel, so it fills 12% of the frame’s short side.
Longer subs
10, 20 and 30 s in Alt-Az; 60 s only in EQ mode, and 60 s is the ceiling. Time for a solid image by sub length:
| Sub length | Bortle 3 | Bortle 5 | Bortle 7 |
|---|---|---|---|
| 10 s | 1 h 26 min518 subs | 1 h 40 min602 subs | 2 h 41 min967 subs |
| 20 s | 1 h 03 min189 subs | 1 h 17 min230 subs | 2 h 18 min413 subs |
| 30 s | 55 min110 subs | 1 h 09 min138 subs | 2 h 10 min260 subs |
| 60 s | 47 min48 subs | 1 h 01 min61 subs | 2 h 02 min122 subs |
With and without the dual-band filter
| Filter | Bortle 3 | Bortle 5 | Bortle 7 |
|---|---|---|---|
| UV/IR-cut (no light-pollution filter) | 1 h 12 min434 subs | 1 h 58 min707 subs | 5 h 17 min1,900 subs |
| dual-band (LP filter) | 1 h 26 min518 subs | 1 h 40 min602 subs | 2 h 41 min967 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 Pro
The S50 optics at 260 mm on an 8 MP 1/1.2-inch sensor: a wider, taller field, four times the pixels, and 60 s subs in EQ mode. Per pixel it is a whisker slower than the S50 because of the longer focal length; the long subs make it the better dark-site scope.
10, 20 and 30 s in Alt-Az; 60 s only in EQ mode, and 60 s is the ceiling. Built-in UV/IR-cut, dual-band (OIII 30 nm / Hα 20 nm) and dark filters on the telephoto camera.
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 Pro? 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 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 Pro