How long to image the M103 with the ZWO Seestar S30 Pro
From a Bortle 6 suburban sky, the ZWO Seestar S30 Pro needs about 7 min (41 subs of 10 s) for a solid image of the M103. A quick look takes 2 min; a showpiece 27 min. Under a Bortle 3 rural sky the solid figure drops to 5 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 4% 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 | 2 min10 subs | 5 min30 subs | 15 min92 subs |
| Bortle 2Typical dark site | 2 min10 subs | 5 min30 subs | 16 min95 subs |
| Bortle 3Rural | 2 min10 subs | 5 min30 subs | 16 min98 subs |
| Bortle 4Rural / suburban transition | 2 min10 subs | 5 min30 subs | 18 min108 subs |
| Bortle 5Suburban | 2 min10 subs | 5 min31 subs | 20 min123 subs |
| Bortle 6Bright suburban | 2 min11 subs | 7 min41 subs | 27 min161 subs |
| Bortle 7Suburban / urban transition | 2 min15 subs | 10 min58 subs | 39 min232 subs |
| Bortle 8City | 4 min22 subs | 14 min86 subs | 57 min343 subs |
| Bortle 9Inner city | 6 min37 subs | 24 min145 subs | 1 h 37 min580 subs |
Power and kit for this session
Allowing for slewing, focusing and rejected subs, that is about 9 min of run time. The Seestar S30 Pro’s battery (rated about 5 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 10000mAh 5V 3A5 V 3 A input and it runs while charging.
- Seestar S30 Pro dew shieldActive anti-dew is built in; a shield adds margin. The S30 Pro front differs from the S30, so check the listing.
- 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 S30 Pro →
How it frames
The M103 is 6′ across. The Seestar S30 Pro frames 3.99° × 2.24° at 3.74″ per pixel, so it fills 4% of the frame’s short side.
Longer subs
10, 20 and 30 s in Alt-Az; 60 s only in EQ mode, which needs the TH10 head. Time for a solid image by sub length:
| Sub length | Bortle 3 | Bortle 5 | Bortle 7 |
|---|---|---|---|
| 10 s | 5 min30 subs | 5 min31 subs | 10 min58 subs |
| 20 s | 10 min30 subs | 10 min30 subs | 10 min30 subs |
| 30 s | 15 min30 subs | 15 min30 subs | 15 min30 subs |
| 60 s | 30 min30 subs | 30 min30 subs | 30 min30 subs |
Leave the dual-band filter out for the M103. It is an open cluster, 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 10 times slower.
About the M103
A small, fan-shaped open cluster in Cassiopeia, the last object in Messier's own list.
NGC 581 · Open cluster in Cassiopeia · magnitude 7.4 · 6′ · best in Sep, Oct, Nov. Reachable from mid-northern latitudes (UK, northern US, central Europe) and from the south.
Open clusters are the easiest targets in the sky. The stars are bright, so the aim is colour and tight stars rather than depth: short subs, no filter, and stop before the bright members saturate. The nominal time here gets you clean star colour; more integration only adds background stars.
About the ZWO Seestar S30 Pro
The S30 optics upgraded to a quadruplet in front of an 8 MP IMX585. Same speed per pixel as the S30, four times the pixels, so you can crop hard.
10, 20 and 30 s in Alt-Az; 60 s only in EQ mode, which needs the TH10 head. 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 M103 from a Seestar S30 Pro? Email it with your total time and sky to [email protected] and it goes here, credited.
Same target, other telescopes
- M103 with the ZWO Seestar S50: 6 min from Bortle 6
- M103 with the ZWO Seestar S50 Pro: 6 min from Bortle 6
- M103 with the ZWO Seestar S30: 6 min from Bortle 6
- M103 with the DwarfLab DWARF 3: 9 min from Bortle 6
- M103 with the DwarfLab DWARF mini: 8 min from Bortle 6
- M103 with the DwarfLab Draco: 15 min from Bortle 6
- M103 with the DwarfLab DWARF II: 19 min from Bortle 6
- M103 with the Vaonis Vespera II: 6 min from Bortle 6
- M103 with the Vaonis Vespera Pro: 13 min from Bortle 6
- M103 with the Vaonis Vespera 3: 6 min from Bortle 6
- M103 with the Vaonis Vespera Pro 2: 12 min from Bortle 6
- M103 with the Unistellar eQuinox 2: 5 min from Bortle 6
- M103 with the Unistellar Odyssey: 20 min from Bortle 6
- M103 with the Celestron Origin: 5 min from Bortle 6
- M103 with the Celestron Origin Mark II: 5 min from Bortle 6
All telescopes for the M103 · All targets for the Seestar S30 Pro