How long to image the NGC 891 with the ZWO Seestar S50 Pro
From a Bortle 6 suburban sky, the ZWO Seestar S50 Pro needs about 3 h (1,079 subs of 10 s) for a solid image of the NGC 891. A quick look takes 45 min; a showpiece 12 h. Under a Bortle 3 rural sky the solid figure drops to 1 h 09 min. At Bortle 6 the limit is skyglow, so a darker site or a filter helps more than longer subs. In this scope's field it fills 16% 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 min87 subs | 58 min347 subs | 3 h 51 min1,386 subs |
| Bortle 2Typical dark site | 15 min93 subs | 1 h 01 min369 subs | 4 h 06 min1,476 subs |
| Bortle 3Rural | 17 min103 subs | 1 h 09 min412 subs | 4 h 34 min1,646 subs |
| Bortle 4Rural / suburban transition | 21 min129 subs | 1 h 26 min515 subs | 5 h 43 min2,058 subs |
| Bortle 5Suburban | 28 min170 subs | 1 h 53 min678 subs | 7 h 32 min2,711 subs |
| Bortle 6Bright suburban | 45 min270 subs | 3 h1,079 subs | 12 h4,313 subs |
| Bortle 7Suburban / urban transition | 1 h 17 min461 subs | 5 h 07 min1,842 subs | 20 h7,365 subs |
| Bortle 8City | 2 h 06 min757 subs | 8 h 24 min3,026 subs | 34 h12,104 subs |
| Bortle 9Inner city | 3 h 51 min1,389 subs | 15 h5,553 subs | 62 h22,211 subs |
Power and kit for this session
Allowing for slewing, focusing and rejected subs, that is about 3 h 54 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, and 30% off the battery for a November night.)
- 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.
- hand warmers long lastingAir-activated packs give hours of heat for the person; winter nights are long and you spend most of them standing still.
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Everything that fits the Seestar S50 Pro →
How it frames
The NGC 891 is 13.5′ × 2.5′ across. The Seestar S50 Pro frames 2.45° × 1.38° at 2.30″ per pixel, so it fills 16% 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 09 min412 subs | 1 h 53 min678 subs | 5 h 07 min1,842 subs |
| 20 s | 57 min172 subs | 1 h 42 min306 subs | 4 h 56 min887 subs |
| 30 s | 54 min108 subs | 1 h 38 min196 subs | 4 h 52 min584 subs |
| 60 s | 50 min50 subs | 1 h 34 min95 subs | 4 h 48 min289 subs |
Leave the dual-band filter out for the NGC 891. It is a galaxy, and it shines right across the spectrum. A dual-band filter keeps two emission lines and throws the rest away, so most of the light you came for is being stopped along with the sky. From a Bortle 6 sky it would be roughly 12 times slower.
About the NGC 891
A perfect edge-on spiral split by a dust lane. Faint per pixel; a dark sky or a long stack shows the lane.
Caldwell 23, Silver Sliver · Galaxy in Andromeda · magnitude 10.0 · 13.5′ × 2.5′ · best in Oct, Nov, Dec. Reachable from mid-northern latitudes (UK, northern US, central Europe) and from the south.
Galaxies are broadband targets: their light is mostly starlight spread across the spectrum, so a dual-band filter throws most of it away and makes things slower, not faster. Shoot without a filter (or with a plain UV/IR cut) and rely on total time and a dark sky. The core of a galaxy is usually many times brighter than its outer disc, so a short stack shows the nucleus long before the arms; the figures here are for the arms and disc, not the core.
Field rotation in Alt-Az mode crops the edges of the stack over a long session, so on a big galaxy re-centre now and then or use EQ mode where your scope supports it.
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 NGC 891 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
- NGC 891 with the ZWO Seestar S50: 2 h 44 min from Bortle 6
- NGC 891 with the ZWO Seestar S30: 2 h 53 min from Bortle 6
- NGC 891 with the ZWO Seestar S30 Pro: 3 h 10 min from Bortle 6
- NGC 891 with the DwarfLab DWARF 3: 3 h 58 min from Bortle 6
- NGC 891 with the DwarfLab DWARF mini: 2 h 43 min from Bortle 6
- NGC 891 with the DwarfLab Draco: 2 h 15 min from Bortle 6
- NGC 891 with the DwarfLab DWARF II: 9 h 24 min from Bortle 6
- NGC 891 with the Vaonis Vespera II: 2 h 44 min from Bortle 6
- NGC 891 with the Vaonis Vespera Pro: 6 h 08 min from Bortle 6
- NGC 891 with the Vaonis Vespera 3: 2 h 37 min from Bortle 6
- NGC 891 with the Vaonis Vespera Pro 2: 5 h 51 min from Bortle 6
- NGC 891 with the Unistellar eQuinox 2: 2 h 30 min from Bortle 6
- NGC 891 with the Unistellar Odyssey: 12 h from Bortle 6
- NGC 891 with the Celestron Origin: 43 min from Bortle 6
- NGC 891 with the Celestron Origin Mark II: 59 min from Bortle 6
All telescopes for the NGC 891 · All targets for the Seestar S50 Pro