How long to image the M22 with the ZWO Seestar S30
From a Bortle 6 suburban sky, the ZWO Seestar S30 needs about 13 min (78 subs of 10 s) for a solid image of the M22. A quick look takes 3 min; a showpiece 51 min. Under a Bortle 3 rural sky the solid figure drops to 6 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 45% 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 | 6 min35 subs | 23 min138 subs |
| Bortle 2Typical dark site | 2 min10 subs | 6 min36 subs | 24 min144 subs |
| Bortle 3Rural | 2 min10 subs | 6 min39 subs | 26 min154 subs |
| Bortle 4Rural / suburban transition | 2 min12 subs | 7 min45 subs | 30 min178 subs |
| Bortle 5Suburban | 2 min14 subs | 9 min54 subs | 36 min215 subs |
| Bortle 6Bright suburban | 3 min20 subs | 13 min78 subs | 51 min309 subs |
| Bortle 7Suburban / urban transition | 5 min31 subs | 20 min122 subs | 1 h 21 min486 subs |
| Bortle 8City | 8 min48 subs | 32 min191 subs | 2 h 07 min761 subs |
| Bortle 9Inner city | 14 min85 subs | 56 min338 subs | 3 h 45 min1,349 subs |
Power and kit for this session
Allowing for slewing, focusing and rejected subs, that is about 17 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 M22 is 32′ across. The Seestar S30 frames 2.13° × 1.20° at 3.99″ per pixel, so it fills 45% 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 | 6 min39 subs | 9 min54 subs | 20 min122 subs |
| 20 s | 10 min30 subs | 10 min30 subs | 19 min59 subs |
| 30 s | 15 min30 subs | 15 min30 subs | 19 min39 subs |
| 60 s | 30 min30 subs | 30 min30 subs | 30 min30 subs |
Leave the dual-band filter out for the M22. 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 M22
One of the brightest globulars in the sky, outshining M13, but low from northern Europe. Superb from the south.
NGC 6656 · Globular cluster in Sagittarius · magnitude 5.1 · 32′ · 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
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 M22 from a Seestar S30? Email it with your total time and sky to [email protected] and it goes here, credited.
Same target, other telescopes
- M22 with the ZWO Seestar S50: 12 min from Bortle 6
- M22 with the ZWO Seestar S50 Pro: 13 min from Bortle 6
- M22 with the ZWO Seestar S30 Pro: 14 min from Bortle 6
- M22 with the DwarfLab DWARF 3: 18 min from Bortle 6
- M22 with the DwarfLab DWARF mini: 12 min from Bortle 6
- M22 with the DwarfLab Draco: 15 min from Bortle 6
- M22 with the DwarfLab DWARF II: 41 min from Bortle 6
- M22 with the Vaonis Vespera II: 12 min from Bortle 6
- M22 with the Vaonis Vespera Pro: 27 min from Bortle 6
- M22 with the Vaonis Vespera 3: 12 min from Bortle 6
- M22 with the Vaonis Vespera Pro 2: 26 min from Bortle 6
- M22 with the Unistellar eQuinox 2: 11 min from Bortle 6
- M22 with the Unistellar Odyssey: 48 min from Bortle 6
- M22 with the Celestron Origin: 5 min from Bortle 6
- M22 with the Celestron Origin Mark II: 5 min from Bortle 6
All telescopes for the M22 · All targets for the Seestar S30