How long to image the NGC 2403 with the ZWO Seestar S50
From a Bortle 6 suburban sky, the ZWO Seestar S50 needs about 3 h 13 min (1,161 subs of 10 s) for a solid image of the NGC 2403. A quick look takes 48 min; a showpiece 13 h. Under a Bortle 3 rural sky the solid figure drops to 1 h 11 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 49% 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 | 15 min90 subs | 59 min357 subs | 3 h 58 min1,427 subs |
| Bortle 2Typical dark site | 16 min96 subs | 1 h 04 min382 subs | 4 h 14 min1,526 subs |
| Bortle 3Rural | 18 min108 subs | 1 h 11 min429 subs | 4 h 45 min1,713 subs |
| Bortle 4Rural / suburban transition | 23 min136 subs | 1 h 30 min542 subs | 6 h 01 min2,165 subs |
| Bortle 5Suburban | 30 min181 subs | 2 h721 subs | 8 h2,883 subs |
| Bortle 6Bright suburban | 48 min291 subs | 3 h 13 min1,161 subs | 13 h4,642 subs |
| Bortle 7Suburban / urban transition | 1 h 23 min500 subs | 5 h 33 min1,999 subs | 22 h7,996 subs |
| Bortle 8City | 2 h 18 min826 subs | 9 h 10 min3,301 subs | 37 h13,202 subs |
| Bortle 9Inner city | 4 h 13 min1,520 subs | 17 h6,077 subs | 68 h24,306 subs |
Power and kit for this session
Allowing for slewing, focusing and rejected subs, that is about 4 h 11 min of run time. The Seestar S50’s battery is rated at about 6 h, less near freezing, which is cutting it fine; take a power bank. (Bortle 6, solid image; we allow 30% over the integration time, and 30% off the battery for a January night.)
- 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.
- 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 →
How it frames
The NGC 2403 is 21′ × 12′ across. The Seestar S50 frames 1.28° × 0.72° at 2.39″ per pixel, so it fills 49% 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 11 min429 subs | 2 h721 subs | 5 h 33 min1,999 subs |
| 20 s | 1 h180 subs | 1 h 49 min327 subs | 5 h 22 min966 subs |
| 30 s | 56 min113 subs | 1 h 45 min210 subs | 5 h 18 min636 subs |
| 60 s | 52 min53 subs | 1 h 41 min102 subs | 5 h 14 min315 subs |
Leave the dual-band filter out for the NGC 2403. 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 2403
A big, loose spiral in Camelopardalis that looks like a small M33, with bright H II regions dual-band can pick out.
Caldwell 7 · Galaxy in Camelopardalis · magnitude 8.9 · 21′ × 12′ · best in Dec, Jan, Feb. 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
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 NGC 2403 from a Seestar S50? Email it with your total time and sky to [email protected] and it goes here, credited.
Same target, other telescopes
- NGC 2403 with the ZWO Seestar S50 Pro: 3 h 32 min from Bortle 6
- NGC 2403 with the ZWO Seestar S30: 3 h 23 min from Bortle 6
- NGC 2403 with the ZWO Seestar S30 Pro: 3 h 44 min from Bortle 6
- NGC 2403 with the DwarfLab DWARF 3: 4 h 40 min from Bortle 6
- NGC 2403 with the DwarfLab DWARF mini: 3 h 13 min from Bortle 6
- NGC 2403 with the DwarfLab Draco: 2 h 39 min from Bortle 6
- NGC 2403 with the DwarfLab DWARF II: 11 h from Bortle 6
- NGC 2403 with the Vaonis Vespera II: 3 h 13 min from Bortle 6
- NGC 2403 with the Vaonis Vespera Pro: 7 h 14 min from Bortle 6
- NGC 2403 with the Vaonis Vespera 3: 3 h 05 min from Bortle 6
- NGC 2403 with the Vaonis Vespera Pro 2: 6 h 53 min from Bortle 6
- NGC 2403 with the Unistellar eQuinox 2: 2 h 57 min from Bortle 6
- NGC 2403 with the Unistellar Odyssey: 14 h from Bortle 6
- NGC 2403 with the Celestron Origin: 51 min from Bortle 6
- NGC 2403 with the Celestron Origin Mark II: 1 h 10 min from Bortle 6
All telescopes for the NGC 2403 · All targets for the Seestar S50