How long to image the M28 with the ZWO Seestar S30 Pro
From a Bortle 6 suburban sky, the ZWO Seestar S30 Pro needs about 7 min (44 subs of 10 s) for a solid image of the M28. A quick look takes 2 min; a showpiece 29 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 8% 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 min90 subs |
| Bortle 2Typical dark site | 2 min10 subs | 5 min30 subs | 15 min92 subs |
| Bortle 3Rural | 2 min10 subs | 5 min30 subs | 16 min97 subs |
| Bortle 4Rural / suburban transition | 2 min10 subs | 5 min30 subs | 18 min109 subs |
| Bortle 5Suburban | 2 min10 subs | 5 min32 subs | 21 min128 subs |
| Bortle 6Bright suburban | 2 min11 subs | 7 min44 subs | 29 min174 subs |
| Bortle 7Suburban / urban transition | 3 min17 subs | 11 min66 subs | 44 min262 subs |
| Bortle 8City | 4 min25 subs | 17 min100 subs | 1 h 06 min399 subs |
| Bortle 9Inner city | 7 min44 subs | 29 min173 subs | 1 h 55 min690 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 M28 is 11′ across. The Seestar S30 Pro frames 3.99° × 2.24° at 3.74″ per pixel, so it fills 8% 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 min32 subs | 11 min66 subs |
| 20 s | 10 min30 subs | 10 min30 subs | 11 min32 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 M28. 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 11 times slower.
About the M28
A compact globular near Lambda Sagittarii, a degree from M22. Small and quick.
NGC 6626 · Globular cluster in Sagittarius · magnitude 6.8 · 11′ · best in Jun, Jul, Aug. 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 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 M28 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
- M28 with the ZWO Seestar S50: 6 min from Bortle 6
- M28 with the ZWO Seestar S50 Pro: 7 min from Bortle 6
- M28 with the ZWO Seestar S30: 7 min from Bortle 6
- M28 with the DwarfLab DWARF 3: 9 min from Bortle 6
- M28 with the DwarfLab DWARF mini: 8 min from Bortle 6
- M28 with the DwarfLab Draco: 15 min from Bortle 6
- M28 with the DwarfLab DWARF II: 20 min from Bortle 6
- M28 with the Vaonis Vespera II: 6 min from Bortle 6
- M28 with the Vaonis Vespera Pro: 14 min from Bortle 6
- M28 with the Vaonis Vespera 3: 6 min from Bortle 6
- M28 with the Vaonis Vespera Pro 2: 13 min from Bortle 6
- M28 with the Unistellar eQuinox 2: 5 min from Bortle 6
- M28 with the Unistellar Odyssey: 23 min from Bortle 6
- M28 with the Celestron Origin: 5 min from Bortle 6
- M28 with the Celestron Origin Mark II: 5 min from Bortle 6
All telescopes for the M28 · All targets for the Seestar S30 Pro