How long to image the M55 with the DwarfLab DWARF mini
From a Bortle 6 suburban sky, the DwarfLab DWARF mini needs about 14 min (55 subs of 15 s) for a solid image of the M55. A quick look takes 3 min; a showpiece 55 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 26% 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 | 3 min10 subs | 8 min30 subs | 23 min91 subs |
| Bortle 2Typical dark site | 3 min10 subs | 8 min30 subs | 24 min95 subs |
| Bortle 3Rural | 3 min10 subs | 8 min30 subs | 26 min103 subs |
| Bortle 4Rural / suburban transition | 3 min10 subs | 8 min31 subs | 30 min121 subs |
| Bortle 5Suburban | 3 min10 subs | 9 min38 subs | 37 min149 subs |
| Bortle 6Bright suburban | 3 min14 subs | 14 min55 subs | 55 min220 subs |
| Bortle 7Suburban / urban transition | 6 min23 subs | 22 min89 subs | 1 h 28 min354 subs |
| Bortle 8City | 9 min36 subs | 35 min141 subs | 2 h 20 min562 subs |
| Bortle 9Inner city | 16 min63 subs | 1 h 03 min252 subs | 4 h 11 min1,006 subs |
Power and kit for this session
Allowing for slewing, focusing and rejected subs, that is about 18 min of run time. The DWARF mini’s battery (rated about 3 h 30 min) 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 PD power bank 10000mAh 20W7,000 mAh inside, about four hours; a PD bank extends the night.
- 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 DWARF mini →
How it frames
The M55 is 19′ across. The DWARF mini frames 2.13° × 1.20° at 3.99″ per pixel, so it fills 26% of the frame’s short side.
Longer subs
Auto mode caps subs at 15 s; 30 s and longer need EQ mode, and 90 s is the ceiling. Time for a solid image by sub length:
| Sub length | Bortle 3 | Bortle 5 | Bortle 7 |
|---|---|---|---|
| 15 s | 8 min30 subs | 9 min38 subs | 22 min89 subs |
| 30 s | 15 min30 subs | 15 min30 subs | 21 min43 subs |
| 60 s | 30 min30 subs | 30 min30 subs | 30 min30 subs |
| 90 s | 45 min30 subs | 45 min30 subs | 45 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 11 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 DwarfLab DWARF mini
DwarfLab’s answer to the Seestar S30: same sensor and focal length, big pixels, dual-band filter built in, and 90 s subs in EQ mode. Sensitivity over megapixels.
Auto mode caps subs at 15 s; 30 s and longer need EQ mode, and 90 s is the ceiling. Built-in Astro (430 to 690 nm), dark-frame and dual-band Hα / OIII filters; no plain VIS filter on the tele camera.
Longer subs matter most under dark skies, where read noise rather than skyglow sets the floor. From a city the difference between 15 s and 90 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 DWARF mini? 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 ZWO Seestar S30 Pro: 16 min from Bortle 6
- M55 with the DwarfLab DWARF 3: 20 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