How long to image the M4 with the ZWO Seestar S30
From a Bortle 6 suburban sky, the ZWO Seestar S30 needs about 1 h 18 min (469 subs of 10 s) for a solid image of the M4. A quick look takes 20 min; a showpiece 5 h 12 min. Under a Bortle 3 rural sky the solid figure drops to 33 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 50% 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 | 7 min43 subs | 28 min171 subs | 1 h 54 min684 subs |
| Bortle 2Typical dark site | 8 min46 subs | 30 min181 subs | 2 h721 subs |
| Bortle 3Rural | 8 min50 subs | 33 min198 subs | 2 h 12 min790 subs |
| Bortle 4Rural / suburban transition | 10 min60 subs | 40 min240 subs | 2 h 39 min957 subs |
| Bortle 5Suburban | 13 min77 subs | 51 min306 subs | 3 h 24 min1,223 subs |
| Bortle 6Bright suburban | 20 min118 subs | 1 h 18 min469 subs | 5 h 12 min1,873 subs |
| Bortle 7Suburban / urban transition | 32 min195 subs | 2 h 10 min779 subs | 8 h 39 min3,113 subs |
| Bortle 8City | 52 min315 subs | 3 h 30 min1,260 subs | 14 h5,039 subs |
| Bortle 9Inner city | 1 h 35 min572 subs | 6 h 21 min2,287 subs | 25 h9,145 subs |
Power and kit for this session
Allowing for slewing, focusing and rejected subs, that is about 1 h 41 min of run time. The Seestar S30’s battery (rated about 6 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 3A6,000 mAh inside; a 10,000 mAh 5 V 3 A bank roughly doubles a session.
- Seestar S30 dew shieldHeater is built in; a cheap shield reduces dew and stray light.
- 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 →
How it frames
The M4 is 36′ across. The Seestar S30 frames 2.13° × 1.20° at 3.99″ per pixel, so it fills 50% 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 | 33 min198 subs | 51 min306 subs | 2 h 10 min779 subs |
| 20 s | 27 min81 subs | 45 min135 subs | 2 h 04 min371 subs |
| 30 s | 25 min50 subs | 43 min86 subs | 2 h 02 min244 subs |
| 60 s | 30 min30 subs | 41 min41 subs | 2 h120 subs |
Leave the dual-band filter out for the M4. It is a globular 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 13 times slower.
About the M4
The loose globular next to Antares. Low in the sky from the UK, so image it near transit.
NGC 6121 · Globular cluster in Scorpius · magnitude 5.9 · 36′ · best in May, Jun, Jul. Reachable from mid-northern latitudes (UK, northern US, central Europe) and from the south.
Globular clusters are point sources packed tight, so they come quickly: the core resolves into stars within a handful of minutes on any smart scope. More time deepens the halo and pulls in the faint outer members. Use short subs so the core does not saturate into a white blob, and no filter.
About the ZWO Seestar S30
Wider and lighter than the S50 with the same 2.9 µm pixels, so its per-pixel speed on extended targets is close despite the smaller aperture. Ideal for big nebulae.
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.
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 M4 from a Seestar S30? Email it with your total time and sky to [email protected] and it goes here, credited.
Same target, other telescopes
- M4 with the ZWO Seestar S50: 1 h 14 min from Bortle 6
- M4 with the ZWO Seestar S50 Pro: 1 h 21 min from Bortle 6
- M4 with the ZWO Seestar S30 Pro: 1 h 26 min from Bortle 6
- M4 with the DwarfLab DWARF 3: 1 h 48 min from Bortle 6
- M4 with the DwarfLab DWARF mini: 1 h 14 min from Bortle 6
- M4 with the DwarfLab Draco: 1 h 01 min from Bortle 6
- M4 with the DwarfLab DWARF II: 4 h 14 min from Bortle 6
- M4 with the Vaonis Vespera II: 1 h 14 min from Bortle 6
- M4 with the Vaonis Vespera Pro: 2 h 46 min from Bortle 6
- M4 with the Vaonis Vespera 3: 1 h 11 min from Bortle 6
- M4 with the Vaonis Vespera Pro 2: 2 h 39 min from Bortle 6
- M4 with the Unistellar eQuinox 2: 1 h 07 min from Bortle 6
- M4 with the Unistellar Odyssey: 5 h 11 min from Bortle 6
- M4 with the Celestron Origin: 20 min from Bortle 6
- M4 with the Celestron Origin Mark II: 27 min from Bortle 6