How long to image the Cat's Eye Nebula with the ZWO Seestar S50 Pro
From a Bortle 6 suburban sky, the ZWO Seestar S50 Pro needs about 11 min (69 subs of 10 s with the built-in dual-band (LP filter) filter) for a solid image of the Cat's Eye Nebula. A quick look takes 3 min; a showpiece 45 min. Under a Bortle 3 rural sky the solid figure drops to 9 min. At Bortle 6 the limit is a mix of skyglow and read noise. In this scope's field it is small in the frame, about 10 pixels across.
| Sky | Quick lookTarget obvious, still noisy | SolidClean enough to share | ShowpieceSmooth faint detail, print-worthy |
|---|---|---|---|
| Bortle 1Excellent dark site | 2 min14 subs | 9 min56 subs | 37 min223 subs |
| Bortle 2Typical dark site | 2 min15 subs | 9 min57 subs | 37 min225 subs |
| Bortle 3Rural | 2 min15 subs | 9 min57 subs | 38 min228 subs |
| Bortle 4Rural / suburban transition | 2 min15 subs | 10 min59 subs | 39 min235 subs |
| Bortle 5Suburban | 3 min16 subs | 10 min62 subs | 41 min246 subs |
| Bortle 6Bright suburban | 3 min18 subs | 11 min69 subs | 45 min273 subs |
| Bortle 7Suburban / urban transition | 3 min21 subs | 14 min82 subs | 54 min325 subs |
| Bortle 8City | 4 min26 subs | 17 min102 subs | 1 h 08 min406 subs |
| Bortle 9Inner city | 6 min37 subs | 24 min145 subs | 1 h 36 min579 subs |
Power and kit for this session
Allowing for slewing, focusing and rejected subs, that is about 15 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 Cat's Eye Nebula is 0.4′ × 0.3′ across. The Seestar S50 Pro frames 2.45° × 1.38° at 2.30″ per pixel, so it is small in the frame, about 10 pixels across. It is worth doing, but the result is a crop rather than a full frame; a longer focal length would resolve more of it.
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 | 9 min57 subs | 10 min62 subs | 14 min82 subs |
| 20 s | 10 min30 subs | 10 min30 subs | 12 min37 subs |
| 30 s | 15 min30 subs | 15 min30 subs | 15 min30 subs |
| 60 s | 30 min30 subs | 30 min30 subs | 30 min30 subs |
With and without the dual-band filter
| Filter | Bortle 3 | Bortle 5 | Bortle 7 |
|---|---|---|---|
| UV/IR-cut (no light-pollution filter) | 7 min44 subs | 10 min59 subs | 21 min124 subs |
| dual-band (LP filter) | 9 min57 subs | 10 min62 subs | 14 min82 subs |
About the Cat's Eye Nebula
A tiny, intensely bright planetary. The core saturates in seconds; the faint outer halo around it is a long dual-band project.
NGC 6543, Caldwell 6 · Planetary nebula in Draco · magnitude 9.0 · 0.4′ × 0.3′ · best in May, Jun, Jul. Reachable from mid-northern latitudes (UK, northern US, central Europe) and from the south.
Planetary nebulae are small but intensely bright per pixel in OIII and H-alpha, so they respond very well to a dual-band filter and do not need much time for the main shell. The faint outer halos most of them have are a different proposition and need hours. Keep subs short if the central region saturates.
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 Cat's Eye Nebula 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
- Cat's Eye Nebula with the ZWO Seestar S50: 10 min from Bortle 6
- Cat's Eye Nebula with the ZWO Seestar S30: 11 min from Bortle 6
- Cat's Eye Nebula with the ZWO Seestar S30 Pro: 12 min from Bortle 6
- Cat's Eye Nebula with the DwarfLab DWARF 3: 14 min from Bortle 6
- Cat's Eye Nebula with the DwarfLab DWARF mini: 10 min from Bortle 6
- Cat's Eye Nebula with the DwarfLab Draco: 15 min from Bortle 6
- Cat's Eye Nebula with the DwarfLab DWARF II: 40 min from Bortle 6
- Cat's Eye Nebula with the Vaonis Vespera II: 12 min from Bortle 6
- Cat's Eye Nebula with the Vaonis Vespera Pro: 27 min from Bortle 6
- Cat's Eye Nebula with the Vaonis Vespera 3: 12 min from Bortle 6
- Cat's Eye Nebula with the Vaonis Vespera Pro 2: 26 min from Bortle 6
- Cat's Eye Nebula with the Unistellar eQuinox 2: 10 min from Bortle 6
- Cat's Eye Nebula with the Unistellar Odyssey: 46 min from Bortle 6
- Cat's Eye Nebula with the Celestron Origin: 5 min from Bortle 6
- Cat's Eye Nebula with the Celestron Origin Mark II: 5 min from Bortle 6
All telescopes for the Cat's Eye Nebula · All targets for the Seestar S50 Pro