How long to image the M70 with the ZWO Seestar S50
From a Bortle 6 suburban sky, the ZWO Seestar S50 needs about 16 min (99 subs of 10 s) for a solid image of the M70. A quick look takes 4 min; a showpiece 1 h 06 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 19% 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 min12 subs | 7 min45 subs | 29 min177 subs |
| Bortle 2Typical dark site | 2 min12 subs | 8 min46 subs | 31 min184 subs |
| Bortle 3Rural | 2 min13 subs | 8 min50 subs | 33 min197 subs |
| Bortle 4Rural / suburban transition | 2 min15 subs | 9 min57 subs | 38 min227 subs |
| Bortle 5Suburban | 3 min18 subs | 11 min69 subs | 46 min275 subs |
| Bortle 6Bright suburban | 4 min25 subs | 16 min99 subs | 1 h 06 min394 subs |
| Bortle 7Suburban / urban transition | 6 min39 subs | 26 min155 subs | 1 h 43 min620 subs |
| Bortle 8City | 10 min61 subs | 40 min243 subs | 2 h 42 min970 subs |
| Bortle 9Inner city | 18 min108 subs | 1 h 12 min430 subs | 4 h 46 min1,718 subs |
Power and kit for this session
Allowing for slewing, focusing and rejected subs, that is about 21 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.
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Everything that fits the Seestar S50 →
How it frames
The M70 is 8′ across. The Seestar S50 frames 1.28° × 0.72° at 2.39″ per pixel, so it fills 19% 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 | 8 min50 subs | 11 min69 subs | 26 min155 subs |
| 20 s | 10 min30 subs | 11 min33 subs | 25 min76 subs |
| 30 s | 15 min30 subs | 15 min30 subs | 25 min50 subs |
| 60 s | 30 min30 subs | 30 min30 subs | 30 min30 subs |
Leave the dual-band filter out for the M70. 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 M70
M69's near twin two degrees east, a compact globular in the same low field.
NGC 6681 · Globular cluster in Sagittarius · magnitude 7.9 · 8′ · 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 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 M70 from a Seestar S50? Email it with your total time and sky to [email protected] and it goes here, credited.
Same target, other telescopes
- M70 with the ZWO Seestar S50 Pro: 18 min from Bortle 6
- M70 with the ZWO Seestar S30: 17 min from Bortle 6
- M70 with the ZWO Seestar S30 Pro: 19 min from Bortle 6
- M70 with the DwarfLab DWARF 3: 24 min from Bortle 6
- M70 with the DwarfLab DWARF mini: 16 min from Bortle 6
- M70 with the DwarfLab Draco: 15 min from Bortle 6
- M70 with the DwarfLab DWARF II: 54 min from Bortle 6
- M70 with the Vaonis Vespera II: 16 min from Bortle 6
- M70 with the Vaonis Vespera Pro: 36 min from Bortle 6
- M70 with the Vaonis Vespera 3: 16 min from Bortle 6
- M70 with the Vaonis Vespera Pro 2: 35 min from Bortle 6
- M70 with the Unistellar eQuinox 2: 14 min from Bortle 6
- M70 with the Unistellar Odyssey: 1 h 03 min from Bortle 6
- M70 with the Celestron Origin: 5 min from Bortle 6
- M70 with the Celestron Origin Mark II: 6 min from Bortle 6
All telescopes for the M70 · All targets for the Seestar S50