How long to image the M55 with the ZWO Seestar S30 Pro
From a Bortle 6 suburban sky, the ZWO Seestar S30 Pro needs about 16 min (96 subs of 10 s) for a solid image of the M55. A quick look takes 4 min; a showpiece 1 h 04 min. Under a Bortle 3 rural sky the solid figure drops to 8 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 14% 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 min11 subs | 7 min41 subs | 27 min163 subs |
| Bortle 2Typical dark site | 2 min11 subs | 7 min43 subs | 28 min170 subs |
| Bortle 3Rural | 2 min12 subs | 8 min46 subs | 30 min183 subs |
| Bortle 4Rural / suburban transition | 2 min14 subs | 9 min54 subs | 35 min213 subs |
| Bortle 5Suburban | 3 min17 subs | 11 min66 subs | 44 min262 subs |
| Bortle 6Bright suburban | 4 min24 subs | 16 min96 subs | 1 h 04 min382 subs |
| Bortle 7Suburban / urban transition | 6 min39 subs | 25 min153 subs | 1 h 42 min611 subs |
| Bortle 8City | 10 min61 subs | 40 min242 subs | 2 h 41 min966 subs |
| Bortle 9Inner city | 18 min108 subs | 1 h 12 min431 subs | 4 h 47 min1,724 subs |
Power and kit for this session
Allowing for slewing, focusing and rejected subs, that is about 21 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 M55 is 19′ across. The Seestar S30 Pro frames 3.99° × 2.24° at 3.74″ per pixel, so it fills 14% 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 | 8 min46 subs | 11 min66 subs | 25 min153 subs |
| 20 s | 10 min30 subs | 10 min31 subs | 25 min74 subs |
| 30 s | 15 min30 subs | 15 min30 subs | 24 min49 subs |
| 60 s | 30 min30 subs | 30 min30 subs | 30 min30 subs |
Leave the dual-band filter out for the M55. 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 12 times slower.
About the M55
A large, loose globular that resolves easily but sits low for northern imagers.
NGC 6809 · Globular cluster in Sagittarius · magnitude 6.3 · 19′ · 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 M55 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
- M55 with the ZWO Seestar S50: 14 min from Bortle 6
- M55 with the ZWO Seestar S50 Pro: 15 min from Bortle 6
- M55 with the ZWO Seestar S30: 14 min from Bortle 6
- M55 with the DwarfLab DWARF 3: 20 min from Bortle 6
- M55 with the DwarfLab DWARF mini: 14 min from Bortle 6
- M55 with the DwarfLab Draco: 15 min from Bortle 6
- M55 with the DwarfLab DWARF II: 46 min from Bortle 6
- M55 with the Vaonis Vespera II: 14 min from Bortle 6
- M55 with the Vaonis Vespera Pro: 31 min from Bortle 6
- M55 with the Vaonis Vespera 3: 13 min from Bortle 6
- M55 with the Vaonis Vespera Pro 2: 29 min from Bortle 6
- M55 with the Unistellar eQuinox 2: 12 min from Bortle 6
- M55 with the Unistellar Odyssey: 54 min from Bortle 6
- M55 with the Celestron Origin: 5 min from Bortle 6
- M55 with the Celestron Origin Mark II: 5 min from Bortle 6
All telescopes for the M55 · All targets for the Seestar S30 Pro