How long to image the M25 with the DwarfLab DWARF mini
From a Bortle 6 suburban sky, the DwarfLab DWARF mini needs about 8 min (30 subs of 15 s) for a solid image of the M25. A quick look takes 3 min; a showpiece 23 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 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 | 3 min10 subs | 8 min30 subs | 23 min90 subs |
| Bortle 2Typical dark site | 3 min10 subs | 8 min30 subs | 23 min90 subs |
| Bortle 3Rural | 3 min10 subs | 8 min30 subs | 23 min90 subs |
| Bortle 4Rural / suburban transition | 3 min10 subs | 8 min30 subs | 23 min90 subs |
| Bortle 5Suburban | 3 min10 subs | 8 min30 subs | 23 min90 subs |
| Bortle 6Bright suburban | 3 min10 subs | 8 min30 subs | 23 min90 subs |
| Bortle 7Suburban / urban transition | 3 min10 subs | 8 min30 subs | 23 min90 subs |
| Bortle 8City | 3 min10 subs | 8 min30 subs | 23 min90 subs |
| Bortle 9Inner city | 3 min10 subs | 9 min38 subs | 38 min151 subs |
Power and kit for this session
Allowing for slewing, focusing and rejected subs, that is about 10 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 M25 is 32′ across. The DWARF mini frames 2.13° × 1.20° at 3.99″ per pixel, so it fills 45% 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 | 8 min30 subs | 8 min30 subs |
| 30 s | 15 min30 subs | 15 min30 subs | 15 min30 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 M25. It is an open 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 3 times slower.
About the M25
A bright open cluster with a Cepheid variable at its heart. Easy from anywhere it clears the horizon.
IC 4725 · Open cluster in Sagittarius · magnitude 4.6 · 32′ · best in Jun, Jul, Aug. Reachable from mid-northern latitudes (UK, northern US, central Europe) and from the south.
Open clusters are the easiest targets in the sky. The stars are bright, so the aim is colour and tight stars rather than depth: short subs, no filter, and stop before the bright members saturate. The nominal time here gets you clean star colour; more integration only adds background stars.
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 M25 from a DWARF mini? Email it with your total time and sky to [email protected] and it goes here, credited.
Same target, other telescopes
- M25 with the ZWO Seestar S50: 5 min from Bortle 6
- M25 with the ZWO Seestar S50 Pro: 5 min from Bortle 6
- M25 with the ZWO Seestar S30: 5 min from Bortle 6
- M25 with the ZWO Seestar S30 Pro: 5 min from Bortle 6
- M25 with the DwarfLab DWARF 3: 8 min from Bortle 6
- M25 with the DwarfLab Draco: 15 min from Bortle 6
- M25 with the DwarfLab DWARF II: 8 min from Bortle 6
- M25 with the Vaonis Vespera II: 5 min from Bortle 6
- M25 with the Vaonis Vespera Pro: 6 min from Bortle 6
- M25 with the Vaonis Vespera 3: 5 min from Bortle 6
- M25 with the Vaonis Vespera Pro 2: 5 min from Bortle 6
- M25 with the Unistellar eQuinox 2: 2 min from Bortle 6
- M25 with the Unistellar Odyssey: 9 min from Bortle 6
- M25 with the Celestron Origin: 5 min from Bortle 6
- M25 with the Celestron Origin Mark II: 5 min from Bortle 6