How long to image the M72 with the ZWO Seestar S50
From a Bortle 6 suburban sky, the ZWO Seestar S50 needs about 1 h 11 min (429 subs of 10 s) for a solid image of the M72. A quick look takes 18 min; a showpiece 4 h 46 min. Under a Bortle 3 rural sky the solid figure drops to 30 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 | 7 min40 subs | 26 min158 subs | 1 h 45 min631 subs |
| Bortle 2Typical dark site | 7 min42 subs | 28 min166 subs | 1 h 51 min664 subs |
| Bortle 3Rural | 8 min46 subs | 30 min182 subs | 2 h 01 min727 subs |
| Bortle 4Rural / suburban transition | 9 min55 subs | 37 min220 subs | 2 h 27 min880 subs |
| Bortle 5Suburban | 12 min71 subs | 47 min281 subs | 3 h 07 min1,122 subs |
| Bortle 6Bright suburban | 18 min108 subs | 1 h 11 min429 subs | 4 h 46 min1,715 subs |
| Bortle 7Suburban / urban transition | 30 min178 subs | 1 h 58 min711 subs | 7 h 54 min2,844 subs |
| Bortle 8City | 48 min288 subs | 3 h 12 min1,150 subs | 13 h4,599 subs |
| Bortle 9Inner city | 1 h 27 min522 subs | 5 h 47 min2,085 subs | 23 h8,340 subs |
Power and kit for this session
Allowing for slewing, focusing and rejected subs, that is about 1 h 33 min of run time. The Seestar S50’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 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.
Affiliate links: the retailer pays us a small commission and you pay the same price. These are search links to the named product, not endorsements of a particular listing; check the listing matches your model.
Everything that fits the Seestar S50 →
How it frames
The M72 is 6′ across. The Seestar S50 frames 1.28° × 0.72° at 2.39″ 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 (app 2.5 and later). Time for a solid image by sub length:
| Sub length | Bortle 3 | Bortle 5 | Bortle 7 |
|---|---|---|---|
| 10 s | 30 min182 subs | 47 min281 subs | 1 h 58 min711 subs |
| 20 s | 26 min80 subs | 43 min129 subs | 1 h 55 min344 subs |
| 30 s | 25 min51 subs | 42 min84 subs | 1 h 53 min227 subs |
| 60 s | 30 min30 subs | 40 min41 subs | 1 h 52 min113 subs |
Leave the dual-band filter out for the M72. 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 M72
A faint, distant globular in Aquarius. Among the harder Messier globulars.
NGC 6981 · Globular cluster in Aquarius · magnitude 9.3 · 6′ · best in Jul, Aug, Sep. 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 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 M72 from a Seestar S50? Email it with your total time and sky to [email protected] and it goes here, credited.
Same target, other telescopes
- M72 with the ZWO Seestar S50 Pro: 1 h 18 min from Bortle 6
- M72 with the ZWO Seestar S30: 1 h 15 min from Bortle 6
- M72 with the ZWO Seestar S30 Pro: 1 h 23 min from Bortle 6
- M72 with the DwarfLab DWARF 3: 1 h 44 min from Bortle 6
- M72 with the DwarfLab DWARF mini: 1 h 11 min from Bortle 6
- M72 with the DwarfLab Draco: 59 min from Bortle 6
- M72 with the DwarfLab DWARF II: 4 h 02 min from Bortle 6
- M72 with the Vaonis Vespera II: 1 h 11 min from Bortle 6
- M72 with the Vaonis Vespera Pro: 2 h 39 min from Bortle 6
- M72 with the Vaonis Vespera 3: 1 h 08 min from Bortle 6
- M72 with the Vaonis Vespera Pro 2: 2 h 32 min from Bortle 6
- M72 with the Unistellar eQuinox 2: 1 h 04 min from Bortle 6
- M72 with the Unistellar Odyssey: 4 h 51 min from Bortle 6
- M72 with the Celestron Origin: 19 min from Bortle 6
- M72 with the Celestron Origin Mark II: 26 min from Bortle 6
All telescopes for the M72 · All targets for the Seestar S50